Mesenchymal-specific deletion of C/EBPβ suppresses pulmonary fibrosis

Serum Amyloid A3 Promoter-Luciferase Reporter Mice Are Useful for Early Drug-Induced Nephrotoxicity Detection

Early detection of drug-induced kidney injury is essential for drug development. In this study, multiple low-dose aristolochic acid (AA) and cisplatin (Cis) injections increased renal mRNA levels of inflammation, fibrosis, and renal tubule injury markers. We applied a serum amyloid A3 (Saa3) promoter-driven luciferase reporter (Saa3 promoter-luc mice) to these two tubulointerstitial nephritis models and performed in vivo bioluminescence imaging to monitor early renal pathologies. The bioluminescent signals from renal tissues with AA or CIS injections were stronger than those from normal kidney tissues obtained from normal mice. To verify whether the visualized bioluminescence signal was specifically generated by the injured kidney, we performed in vivo bioluminescence analysis after opening the stomachs of Saa3 promoter-luc mice, and the Saa3-mediated bioluminescent signal was specifically detected in the injured kidney. This study showed that Saa3 promoter activity is a potent non-invasive indicator for the early detection of drug-induced nephrotoxicity.

Discoidin domain receptor 2 signaling through PIK3C2α in fibroblasts promotes lung fibrosis

Pulmonary fibrosis, especially idiopathic pulmonary fibrosis (IPF), portends significant morbidity and mortality, and current therapeutic options are suboptimal. We have previously shown that type I collagen signaling through discoidin domain receptor 2 (DDR2), a receptor tyrosine kinase expressed by fibroblasts, is critical for the regulation of fibroblast apoptosis and progressive fibrosis. However, the downstream signaling pathways for DDR2 remain poorly defined and could also be attractive potential targets for therapy. A recent phosphoproteomic approach indicated that PIK3C2α, a poorly studied member of the PI3 kinase family, could be a downstream mediator of DDR2 signaling. We hypothesized that collagen I/DDR2 signaling through PIK3C2α regulates fibroblast activity during progressive fibrosis. To test this hypothesis, we found that primary murine fibroblasts and IPF-derived fibroblasts stimulated with endogenous or exogenous type I collagen led to the formation of a DDR2/PIK3C2α complex, resulting in phosphorylation of PIK3C2α. Fibroblasts treated with an inhibitor of PIK3C2α or with deletion of PIK3C2α had fewer markers of activation after stimulation with TGFβ and more apoptosis after stimulation with a Fas-activating antibody. Finally, mice with fibroblast-specific deletion of PIK3C2α had less fibrosis after bleomycin treatment than did littermate control mice with intact expression of PIK3Cα. Collectively, these data support the notion that collagen/DDR2/PIK3C2α signaling is critical for fibroblast function during progressive fibrosis, making this pathway a potential target for antifibrotic therapy. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

C/EBPβ: The structure, regulation, and its roles in inflammation-related diseases

Inflammation, a mechanism of the human body, has been implicated in many diseases. Inflammatory responses include the release of inflammatory mediators by activating various signaling pathways. CCAAT/enhancer binding protein β (C/EBPβ), a transcription factor in the C/EBP family, contains the leucine zipper (bZIP) domain. The expression of C/EBPβ is mediated at the transcriptional and post-translational levels, such as phosphorylation, acetylation, methylation, and SUMOylation. C/EBPβ has been involved in inflammatory responses by mediating several signaling pathways, such as MAPK/NF-κB and IL-6/JAK/STAT3 pathways. C/EBPβ plays an important role in the pathological development of inflammation-related diseases, such as osteoarthritis, pneumonia, hepatitis, inflammatory bowel diseases, and rheumatoid arthritis. Here, we comprehensively discuss the structure and biological effects of C/EBPβ and its role in inflammatory diseases.

An interferon gamma response signature links myocardial aging and immunosenescence

AIMS

Aging entails profound immunological transformations that can impact myocardial homeostasis and predispose to heart failure. However, preclinical research in the immune-cardiology field is mostly conducted in young healthy animals, which potentially weakens its translational relevance. Herein, we sought to investigate how the aging T-cell compartment associates with changes in myocardial cell biology in aged mice.

METHODS AND RESULTS

We phenotyped the antigen-experienced effector/memory T cells purified from heart-draining lymph nodes of 2-, 6-, 12-, and 18-month-old C57BL/6J mice using single-cell RNA/T cell receptor sequencing. Simultaneously, we profiled all non-cardiomyocyte cell subsets purified from 2- to 18-month-old hearts and integrated our data with publicly available cardiomyocyte single-cell sequencing datasets. Some of these findings were confirmed at the protein level by flow cytometry. With aging, the heart-draining lymph node and myocardial T cells underwent clonal expansion and exhibited an up-regulated pro-inflammatory transcription signature, marked by an increased interferon-γ (IFN-γ) production. In parallel, all major myocardial cell populations showed increased IFN-γ responsive signature with aging. In the aged cardiomyocytes, a stronger IFN-γ response signature was paralleled by the dampening of expression levels of transcripts related to most metabolic pathways, especially oxidative phosphorylation. Likewise, induced pluripotent stem cells-derived cardiomyocytes exposed to chronic, low grade IFN-γ treatment showed a similar inhibition of metabolic activity.

CONCLUSIONS

By investigating the paired age-related alterations in the T cells found in the heart and its draining lymph nodes, we provide evidence for increased myocardial IFN-γ signaling with age, which is associated with inflammatory and metabolic shifts typically seen in heart failure.

P53 regulates CCAAT/Enhancer binding protein β gene expression

BACKGROUND

The transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) is implicated in diverse processes and diseases. Its two isoforms, namely liver-enriched activator protein (LAP) and liver-enriched inhibitor protein (LIP) are translated from the same mRNA. They share the same C-terminal DNA binding domain except LAP has an extra N-terminal activation domain. Probably due to its higher affinity for its DNA cognate sequences, LIP can inhibit LAP transcriptional activity even at substoichiometric levels. However, the regulatory mechanism of C/EBPβ gene expression and the LAP: LIP ratio is unclear.

METHODS

In this study, the C/EBPβ promoter sequence was scanned for conserved P53 response element (P53RE), and binding of P53 to the C/EBPβ promoter was tested by Electrophoretic Mobility Shift Assay (EMSA) and chromatin immunoprecipitation assay. P53 over-expression and dominant negative P53 expression plasmids were transfected into rat lung fibroblasts and tested for C/EBPβ gene transcription and expression. Western blot analysis was used to test the regulation of C/EBPβ LAP and LIP isoforms. Constructs containing the LAP 5'untranslated region (5'UTR) or the LIP 5'UTR region were used to test the importance of 5'UTR in the control of C/EBPβ LAP and LIP translation.

RESULTS

The C/EBPβ promoter sequence was found to contain a conserved P53 response element (P53RE), which binds P53 as demonstrated by Electrophoresis Mobility Shift Assay and chromatin immunoprecipitation assays. P53 over-expression suppressed while dominant negative P53 stimulated C/EBPβ gene transcription and expression. Western blot analysis showed that P53 differentially regulated the translation of the C/EBPβ LAP and LIP isoforms through the regulation of eIF4E and eIF4E-BP1. Further studies with constructs containing the LAP 5'untranslated region (5'UTR) or the LIP 5'UTR region showed that the 5'UTR is important in differential control of C/EBPβ LAP and LIP translation.

CONCLUSION

Analysis of the effects of P53 on C/EBPβ expression revealed a novel mechanism by which P53 could antagonize the effects of C/EBPβ on its target gene expression. For the first time, P53 is shown to be a repressor of C/EBPβ gene expression at both transcriptional and translational levels, with a differential effect in the magnitude of the effect on LAP vs. LIP isoforms.

Insights on the mechanism of bleomycin to induce lung injury and associated in vivo models: A review

Acute lung injury leads to the development of chronic conditions such as idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), asthma as well as alveolar sarcoma. Various investigations are being performed worldwide to understand the pathophysiology of these diseases, develop novel bioactive compounds and inhibitors to target the ailment. Generally, in vivo models are used to understand the disease outcome and therapeutic suppressing effects for which the animals are chemically or physically induced to mimic the onset of definite disease conditions. Amongst the chemical inducing agents, Bleomycin (BLM) is the most successful inducer. It is reported to target various receptors and activate inflammatory pathways, cellular apoptosis, epithelial mesenchymal transition leading to the release of inflammatory cytokines, and proteases. Mice is one of the most widely used animal model for BLM induced pulmonary associated studies apart from rat, rabbit, sheep, pig, and monkey. Although, there is considerable variation amongst in vivo studies for BLM induction which suggests a detailed study on the same to understand the mechanism of action of BLM at molecular level. Hence, herein we have reviewed various chemical inducers, mechanism of action of BLM in inducing lung injury in vivo, its advantages and disadvantages. Further, we have also discussed the rationale behind various in vivo models and recent development in BLM induction for various animals.

Exercise training attenuates angiotensin II-induced cardiac fibrosis by reducing POU2F1 expression

PURPOSE

Exercise training protects against heart failure. However, the mechanism underlying the protective effect of exercise training on angiotensin II (Ang II)-induced cardiac fibrosis remains unclear.

METHODS

An exercise model involving C57BL/6N mice and 6 weeks of treadmill training was used. Ang II (1.44 mg/kg/day) was administered to induce cardiac fibrosis. RNA sequencing and bioinformatic analysis were used to identify the key factors mediating the effects of exercise training on cardiac fibrosis. Primary adult mouse cardiac fibroblasts (CFs) were used in vitro. Adeno-associated virus serotype 9 was used to overexpress POU domain, class 2, transcription factor 1 (POU2F1) in vivo.

RESULTS

Exercise training attenuated Ang II-induced cardiac fibrosis and reversed 39 gene expression changes. The transcription factor regulating the largest number of these genes was POU2F1. Compared to controls, POU2F1 was shown to be significantly upregulated by Ang II, which is itself reduced by exercise training. In vivo, POU2F1 overexpression nullified the benefits of exercise training on cardiac fibrosis. In CFs, POU2F1 promoted cardiac fibrosis. CCAAT enhancer-binding protein β (C/EBPβ) was predicted to be the transcription factor of POU2F1 and verified using a dual-luciferase reporter assay. In vivo, exercise training activated AMP-activated protein kinase (AMPK) and alleviated the increase in C/EBPβ induced by Ang II. In CFs, AMPK agonist inhibited the increase in C/EBPβ and POU2F1 induced by Ang II, whereas AMPK inhibitor reversed this effect.

CONCLUSION

Exercise training attenuates Ang II-induced cardiac fibrosis by reducing POU2F1. Exercise training inhibits POU2F1 by activating AMPK, which is followed by the downregulation of C/EBPβ, the transcription factor of POU2F1.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

KLF4 is a therapeutically tractable brake on fibroblast activation which promotes resolution of pulmonary fibrosis

There is a paucity of information about potential molecular brakes on the activation of fibroblasts that drive tissue fibrosis. The transcription factor Krüppel-like factor 4 (KLF4) is best known as a determinant of cell stemness and a tumor suppressor. We found that its expression was diminished in fibroblasts from fibrotic lung. Gain- and loss-of-function studies showed that KLF4 inhibited fibroblast proliferation, collagen synthesis, and differentiation to myofibroblasts, while restoring their sensitivity to apoptosis. Conditional deletion of KLF4 from fibroblasts potentiated the peak degree of pulmonary fibrosis and abrogated the subsequent spontaneous resolution in a model of transient fibrosis. A small molecule inducer of KLF4 was able to restore its expression in fibrotic fibroblasts and elicit resolution in an experimental model characterized by more clinically relevant persistent pulmonary fibrosis. These data identify KLF4 as a pivotal brake on fibroblast activation whose induction represents a therapeutic approach in fibrosis of the lung and perhaps other organs.

Control of Tissue Fibrosis by 5-Methoxytryptophan, an Innate Anti-Inflammatory Metabolite

Tissue fibrosis causes debilitating human diseases such as liver cirrhosis, heart failure, chronic kidney disease and pulmonary insufficiency. It is a dynamic process orchestrated by specific subsets of monocyte-macrophages, fibroblasts, pericytes and hepatic stellate cells. Fibrosis is linked to tissue inflammation. Pro-inflammatory macrophages promote fibrosis by driving myofibroblast differentiation and macrophage myofibroblast transition. Myofibroblasts express α-smooth muscle cell actin (α-SMA) and secrete extracellular matrix (ECM) proteins notably collagen I and III. Deposition of ECM proteins at injury sites and interstitial tissues distorts normal structure and impairs vital functions. Despite advances in the mechanisms of fibrosis at cellular, molecular and genetic levels, prevention and treatment of fibrotic diseases remain poorly developed. Recent reports suggest that 5-methoxytryptophan (5-MTP) is effective in attenuating injury-induced liver, kidney, cardiac and pulmonary fibrosis. It inhibits macrophage activation and blocks fibroblast differentiation to myofibroblasts. Furthermore, it inhibits hepatic stellate cell differentiation into myofibroblasts. As 5-MTP is an endogenous molecule derived from tryptophan catabolism via tryptophan hydroxylase pathway, it is well-suited as a lead compound for developing new anti-fibrotic drugs. This article provides an overview of 5-MTP synthesis, and a critical review of its anti-fibrotic activities. Its mechanisms of actions and potential therapeutic value will be discussed.

Inducible Depletion of Calpain-2 Mitigates Abdominal Aortic Aneurysm in Mice

[Figure: see text].

TGF-β-induced α-SMA expression is mediated by C/EBPβ acetylation in human alveolar epithelial cells

BACKGROUND

Although the morbidity and mortality rates associated with idiopathic pulmonary fibrosis (IPF) are high, there is still lack of powerful and precise therapeutic options for IPF.

OBJECT

Through in vitro model, this study sought to determine whether binding of acetylated CCAAT/enhancer binding protein β (C/EBPβ) to alpha-smooth muscle actin (α-SMA) promoter could affect the activity of the latter as well as assess if it is essential for epithelial-to-mesenchymal transition (EMT) and extracellular matrix deposition in IPF.

METHODS

The expression of EMT and C/EBPβ in A549 cells treated with transforming growth factor-beta (TGF-β) as pulmonary fibrotic model was detected by western blotting and qPCR. Collagen-I expression using ELISA was performed. The luciferase activity was used to examine the activity of C/EBPβ. Knockdown of C/EBPβ was performed by siRNA. We also investigated the effect of deacetylation of C/EBPβ on EMT using sirtuin 1 (SIRT1). The binding ability of C/EBPβ with α-SMA promoter was affirmed via chromatin immunoprecipitation (ChIP) and electrophoresis mobility shift assay (EMSA). The relationship between α-SMA and acetylated C/EBPβ was determined with co-immunoprecipitation (Co-IP). SiRNA-mediated knockdown of C/EBPβ in A549 cells attenuated TGF-β1-induced myofibroblast differentiation and ECM deposition. The extent of association between acetylated C/EBPβ and α-SMA promoter was dynamically monitored.

RESULTS

It was confirmed that deacetylation of C/EBPβ in A549 cells successfully ameliorated TGF-β1-induced EMT, as shown by reduction in α-SMA expression and excessive collagen-I accumulation.

CONCLUSION

The EMT and fibrotic effect of TGF-β1 is dependent on acetylated C/EBPβ-mediated regulation of α-SMA gene activity. Thus, C/EBPβ acetylation may play a central role in pulmonary fibrosis.

Type I Collagen Signaling Regulates Opposing Fibrotic Pathways through α2β1 Integrin

Fibrosis is characterized by fibroblast activation, leading to matrix remodeling culminating in a stiff, type I collagen-rich fibrotic matrix. Alveolar epithelial cell (AEC) apoptosis is also a major feature of fibrogenesis, and AEC apoptosis is sufficient to initiate a robust lung fibrotic response. TGF-β (transforming growth factor-β) is a major driver of fibrosis and can induce both AEC apoptosis and fibroblast activation. We and others have previously shown that changes in extracellular matrix stiffness and composition can regulate the cellular response to TGF-β. In the present study, we find that type I collagen signaling promotes TGF-β-mediated fibroblast activation and inhibits TGF-β-induced AEC death. Fibroblasts cultured on type I collagen or fibrotic decellularized lung matrix had augmented activation in response to TGF-β, whereas AECs on cultured on type I collagen or fibrotic lung matrix were more resistant to TGF-β-induced apoptosis. Both of these responses were mediated by integrin α₂β₁, a major collagen receptor. AECs treated with an α₂ integrin inhibitor or with deletion of α₂ integrin had loss of collagen-mediated protection from apoptosis. We found that mice with fibroblast-specific deletion of α₂ integrin were protected from fibrosis whereas mice with AEC-specific deletion of α₂ integrin had more lung injury and a greater fibrotic response to bleomycin. Intrapulmonary delivery of an α₂ integrin-activating collagen peptide inhibited AEC apoptosis in vitro and in vivo and attenuated the fibrotic response. These studies underscore the need for a thorough understanding of the divergent response to matrix signaling.

FAK signaling in cancer-associated fibroblasts promotes breast cancer cell migration and metastasis by exosomal miRNAs-mediated intercellular communication

Cancer-associated fibroblasts (CAFs) are activated fibroblasts that constitute the major components of tumor microenvironment (TME) and play crucial roles in tumor development and metastasis. Here, we generated fibroblast-specific inducible focal adhesion kinase (FAK) knockout (cKO) mice in a breast cancer model to study potential role and mechanisms of FAK signaling in CAF to promote breast cancer metastasis in vivo. While not affecting primary tumor development and growth, FAK deletion significantly suppressed breast cancer metastasis in vivo. Analyses of CAFs derived from cKO mice as well as human CAFs showed that FAK is required for their activity to promote mammary tumor cell migration. We further showed that FAK ablation in CAFs decreased their exosome amount and functions to promote tumor cell migration and other activities, which could contribute to the reduced metastasis observed in cKO mice. Lastly, profiling of miRs from CAF exosomes showed alterations of several exosomal miRs in FAK-null CAFs, and further analysis suggested that miR-16 and miR-148a enriched in exosomes from FAK-null CAFs contribute to the reduced tumor cell activities and metastasis. Together, these results identify a new role for FAK signaling in CAFs that regulate their intercellular communication with tumor cells to promote breast cancer metastasis.

The serum amyloid A3 promoter-driven luciferase reporter mice is a valuable tool to image early renal fibrosis development and shows the therapeutic effect of glucosyl-hesperidin treatment

Tubulointerstitial fibrosis is a progressive process affecting the kidneys, causing renal failure that can be life-threatening. Thus, renal fibrosis has become a serious concern in the ageing population; however, fibrotic development cannot be diagnosed early and assessed noninvasively in both patients and experimental animal models. Here, we found that serum amyloid A3 (Saa3) expression is a potent indicator of early renal fibrosis; we also established in vivo Saa3/C/EBPβ-promoter bioluminescence imaging as a sensitive and specific tool for early detection and visualization of tubulointerstitial fibrosis. Saa3 promoter activity is specifically upregulated in parallel with tumor necrosis factor α (TNF-α) and fibrotic marker collagen I in injured kidneys. C/EBPβ, upregulated in injured kidneys and expressed in tubular epithelial cells, is essential for the increased Saa3 promoter activity in response to TNF-α, suggesting that C/EBPβ plays a crucial role in renal fibrosis development. Our model successfully enabled visualization of the suppressive effects of a citrus flavonoid derivative, glucosyl-hesperidin, on inflammation and fibrosis in kidney disease, indicating that this model could be widely used in exploring therapeutic agents for fibrotic diseases.

FOXM1 is a critical driver of lung fibroblast activation and fibrogenesis

While the transcription factor forkhead box M1 (FOXM1) is well known as a proto-oncogene, its potential role in lung fibroblast activation has never been explored. Here, we show that FOXM1 is more highly expressed in fibrotic than in normal lung fibroblasts in humans and mice. FOXM1 was required not only for cell proliferation in response to mitogens, but also for myofibroblast differentiation and apoptosis resistance elicited by TGF-β. The lipid mediator PGE2, acting via cAMP signaling, was identified as an endogenous negative regulator of FOXM1. Finally, genetic deletion of FOXM1 in fibroblasts or administration of the FOXM1 inhibitor Siomycin A in a therapeutic protocol attenuated bleomycin-induced pulmonary fibrosis. Our results identify FOXM1 as a driver of lung fibroblast activation and underscore the therapeutic potential of targeting FOXM1 for pulmonary fibrosis.

Deletion of NF-κB/RelA in Angiotensin II-Sensitive Mesenchymal Cells Blocks Aortic Vascular Inflammation and Abdominal Aortic Aneurysm Formation

OBJECTIVE

Infusion of angiotensin II (Ang II) induces extracellular matrix remodeling and inflammation resulting in abdominal aortic aneurysms (AAAs) in normolipidemic mice. Although Ang II activates mesenchymal cells in the media and adventitia to become fibrogenic, the sentinel role of this mesenchymal population in modulating the inflammatory response and aneurysms is not known. We test the hypothesis that these fibrogenic mesenchymal cells play a critical role in Ang II-induced aortic wall vascular inflammation and AAA formation.

APPROACH AND RESULTS

Ang II infusion increased phospho-Ser536-RelA and interleukin (IL)-6 immunostaining in the abdominal aorta. In addition, aortic mRNA transcripts of RelA-dependent cytokines IL-6 and IL-1β were significantly elevated suggesting that Ang II functionally activates RelA signaling. To test the role of mesenchymal RelA in AAA formation, we generated RelA-CKO mice by administering tamoxifen to double transgenic mice harboring RelA-flox alleles and tamoxifen-inducible Col1a2 promoter-driven Cre recombinase (Col1a2-CreER^T). Tamoxifen administration to Col1a2-CreER^T•mT/mG mice induced Cre expression and RelA depletion in aortic smooth muscle cells and fibroblasts but not in endothelial cells. Infusion of Ang II significantly increased abdominal aortic diameter and the incidence of AAA in RelA wild-type but not in RelA-CKO mice, independent of changes in systolic blood pressure. Furthermore, mesenchymal cell-specific RelA-CKO mice exhibited decreased expression of IL-6 and IL-1β cytokines and decreased recruitment of C68+ and F4/80^lo•Ly6C^hi monocytes during Ang II infusion.

CONCLUSIONS

Fibrogenic mesenchymal RelA plays a causal role in Ang II-induced vascular inflammation and AAA in normolipidemic mice.

Hypoxia-induced ADAM 17 expression is mediated by RSK1-dependent C/EBPβ activation in human lung fibroblasts

Hypoxia was identified as a mediator of lung fibrosis in patients with chronic obstructive asthma (COA). Overexpression of a disintegrin and metalloproteinase 17 (ADAM 17) and connective tissue growth factor (CTGF) leads to development of tissue fibrosis. However, the signaling pathway in hypoxia-induced ADAM 17 expression remains poorly defined. In this study, we investigated the roles that ribosomal S-6 kinase 1 (RSK1)/CCAAT/enhancer-binding protein β (C/EBPβ)-dependent ADAM 17 expression plays in hypoxia-induced CTGF expression in human lung fibroblasts. We observed that hypoxia caused increases in ADAM 17 expression and ADAM 17-luciferase activity in WI-38 cells. Hypoxia-induced CTGF-luciferase activity and CTGF expression were reduced in cells transfected with small interfering (si)RNA of ADAM 17 in WI-38 cells. Moreover, hypoxia-induced ADAM 17 expression was reduced by RSK1 siRNA and C/EBPβ siRNA. Hypoxia caused time-dependent increases in RSK1 phosphorylation at Thr359/Ser363. Exposure of cells to hypoxia resulted in increased C/EBPβ phosphorylation at Thr266 and C/EBPβ-luciferase activity in time-dependent manners, and these effects were suppressed by RSK1 siRNA. Hypoxia induced recruitment of C/EBPβ to the ADAM 17 promoter. Furthermore, CTGF-luciferase activity induced by hypoxia was attenuated by RSK1 siRNA and C/EBPβ siRNA. These results suggest that hypoxia instigates the RSK1-dependent C/EBPβ signaling pathway, which in turn initiates binding of C/EBPβ to the ADAM 17 promoter and ultimately induces ADAM 17 expression in human lung fibroblasts. Moreover, RSK1/C/EBPβ-dependent ADAM 17 expression is involved in hypoxia-induced CTGF expression. Our results suggest possible therapeutic approaches for treating hypoxia-mediated lung fibrosis in COA.

Pulmonary fibrosis requires cell-autonomous mesenchymal fibroblast growth factor (FGF) signaling

Idiopathic pulmonary fibrosis (IPF) is characterized by progressive pulmonary scarring, decline in lung function, and often results in death within 3-5 five years after diagnosis. Fibroblast growth factor (FGF) signaling has been implicated in the pathogenesis of IPF; however, the mechanism through which FGF signaling contributes to pulmonary fibrosis remains unclear. We hypothesized that FGF receptor (FGFR) signaling in fibroblasts is required for the fibrotic response to bleomycin. To test this, mice with mesenchyme-specific tamoxifen-inducible inactivation of FGF receptors 1, 2, and 3 (Col1α2-CreER; TCKO mice) were lineage labeled and administered intratracheal bleomycin. Lungs were collected for histologic analysis, whole lung RNA and protein, and dissociated for flow cytometry and FACS. Bleomycin-treated Col1α2-CreER; TCKO mice have decreased pulmonary fibrosis, collagen production, and fewer α-smooth muscle actin-positive (αSMA+) myofibroblasts compared with controls. Freshly isolated Col1α2-CreER; TCKO mesenchymal cells from bleomycin-treated mice have decreased collagen expression compared with wild type mesenchymal cells. Furthermore, lineage labeled FGFR-deficient fibroblasts have decreased enrichment in fibrotic areas and decreased proliferation. These data identify a cell autonomous requirement for mesenchymal FGFR signaling in the development of pulmonary fibrosis, and for the enrichment of the Col1α2-CreER-positive (Col1α2+) mesenchymal lineage in fibrotic tissue following bleomycin exposure. We conclude that mesenchymal FGF signaling is required for the development of pulmonary fibrosis, and that therapeutic strategies aimed directly at mesenchymal FGF signaling could be beneficial in the treatment of IPF.

The Bleomycin Model of Pulmonary Fibrosis

Interstitial lung disease (ILD) comprises a large number of chronic lung disease characterized by varying degrees of inflammation and fibrosis. Mostly they are idiopathic including idiopathic pulmonary fibrosis (IPF), which is a specific disorder characterized by progressive fibrosis leading commonly to end-stage lung disease, respiratory failure, and fatal outcome. IPF and many of these fibrotic ILDs lack effective therapy despite recent approval of two drugs to slow progression in certain IPF patients. Because there are no natural models for IPF, the use of animal models that reproduce key known features of the disease is warranted. Thus, different animal models have been developed to investigate key mechanisms underlying pathogenesis of pulmonary fibrosis and identify potential therapeutic targets for IPF. While no animal model can recapitulate all features of human disease, several are available to address select features of IPF and other fibrotic ILDs. Historically, among the first to be developed and used widely is the bleomycin model, which is the best-characterized and currently most extensively used animal model due to its ability to reproduce many aspects of IPF and other fibrotic ILDs, good reproducibility, and ease of induction. Studies using the bleomycin model have identified many of the cellular and molecular mechanisms now recognized as being important in pathogenesis of IPF and other fibrotic ILDs, as well as novel therapies for these diseases, including two recent drugs approved for treatment of IPF. This chapter will describe commonly used techniques for induction of the model by endotracheal administration of bleomycin through surgical and nonsurgical (transoral instillation).

Genetic tools for identifying and manipulating fibroblasts in the mouse

The use of mouse genetic tools to track and manipulate fibroblasts has provided invaluable in vivo information regarding the activities of these cells. Recently, many new mouse strains have been described for the specific purpose of studying fibroblast behavior. Colorimetric reporter mice and lines expressing Cre are available for the study of fibroblasts in the organs prone to fibrosis, including heart, kidney, liver, lung, and skeletal muscle. In this review we summarize the current state of the models that have been used to define tissue resident fibroblast populations. While these complex genetic reagents provide unique insights into the process of fibrosis, they also require a thorough understanding of the caveats and limitations. Here, we discuss the specificity and efficiency of the available genetic models and briefly describe how they have been used to document the mechanisms of fibrosis.

Reemergence of hedgehog mediates epithelial-mesenchymal crosstalk in pulmonary fibrosis

Hedgehog signaling plays important roles in cell development and differentiation. In this study, the ability of Sonic Hedgehog (SHH) to induce myofibroblast differentiation was analyzed in isolated human lung fibroblasts, and its in vivo significance was evaluated in rodent bleomycin-induced pulmonary fibrosis. The results showed that SHH could induce myofibroblast differentiation in human lung fibroblasts in a Smo- and Gli1-dependent manner. Gel shift analysis, chromatin immunoprecipitation assay, and site-directed mutagenesis revealed that a Gli1 binding consensus in the α-SMA gene promoter was important for mediating SHH-induced myofibroblast differentiation. Analysis of Hedgehog reemergence in vivo revealed that of all three Hedgehog isoforms, only SHH was significantly induced in bleomycin-injured lung along with Gli1. The induction of SHH was only noted in epithelial cells, and its expression was undetectable in lung fibroblasts or macrophages. transforming growth factor (TGF)-β induced SHH significantly in cultured alveolar epithelial cells, whereas SHH induced TGF-β in lung fibroblasts. Pulmonary fibrosis and α-smooth muscle actin (α-SMA) expression were significantly reduced in mice that were Smo deficient only in type I collagen-expressing cells. Thus, the reemergence of SHH in epithelial cells could result in induction of myofibroblast differentiation in a Smo-dependent manner and subsequent Gli1 activation of the α-SMA promoter.

Conditional Knockout of Telomerase Reverse Transcriptase in Mesenchymal Cells Impairs Mouse Pulmonary Fibrosis

Telomerase is typically expressed in cellular populations capable of extended replication, such as germ cells, tumor cells, and stem cells, but is also induced in tissue injury, repair and fibrosis. Its catalytic component, telomerase reverse transcriptase (TERT) is induced in lung fibroblasts from patients with fibrotic interstitial lung disease and in rodents with bleomycin-induced pulmonary fibrosis. To evaluate the fibroblast specific role of TERT in pulmonary fibrosis, transgenic mice bearing a floxed TERT allele were generated, and then crossed with an inducible collagen α2(I)-Cre mouse line to generate fibroblast specific TERT conditional knockout mice. TERT-specific deficiency in mesenchymal cells caused attenuation of pulmonary fibrosis as manifested by reduced lung hydroxyproline content, type I collagen and α-smooth muscle actin mRNA levels. The TERT-deficient mouse lung fibroblasts displayed decreased cell proliferative capacity and higher susceptibility to induced apoptosis compared with control cells. Additionally TERT deficiency was associated with heightened α-smooth muscle actin expression indicative of myofibroblast differentiation. However the impairment of cell proliferation and increased susceptibility to apoptosis would cause a reduction in the myofibroblast progenitor population necessary to mount a successful myofibroblast-dependent fibrotic response. These findings identified a key role for TERT in fibroblast proliferation and survival essential for pulmonary fibrosis.

Human genome-wide expression analysis reorients the study of inflammatory mediators and biomechanics in osteoarthritis

A major objective of this article is to examine the research implications of recently available genome-wide expression profiles of cartilage from human osteoarthritis (OA) joints. We propose that, when viewed in the light of extensive earlier work, this novel data provides a unique opportunity to reorient the design of experimental systems toward clinical relevance. Specifically, in the area of cartilage explant biology, this will require a fresh evaluation of existing paradigms, so as to optimize the choices of tissue source, cytokine/growth factor/nutrient addition, and biomechanical environment for discovery. Within this context, we firstly discuss the literature on the nature and role of potential catabolic mediators in OA pathology, including data from human OA cartilage, animal models of OA, and ex vivo studies. Secondly, due to the number and breadth of studies on IL-1β in this area, a major focus of the article is a critical analysis of the design and interpretation of cartilage studies where IL-1β has been used as a model cytokine. Thirdly, the article provides a data-driven perspective (including genome-wide analysis of clinical samples, studies on mutant mice, and clinical trials), which concludes that IL-1β should be replaced by soluble mediators such as IL-17 or TGF-β1, which are much more likely to mimic the disease in OA model systems. We also discuss the evidence that changes in early OA can be attributed to the activity of such soluble mediators, whereas late-stage disease results more from a chronic biomechanical effect on the matrix and cells of the remaining cartilage and on other local mediator-secreting cells. Lastly, an updated protocol for in vitro studies with cartilage explants and chondrocytes (including the use of specific gene expression arrays) is provided to motivate more disease-relevant studies on the interplay of cytokines, growth factors, and biomechanics on cellular behavior.

Mesenchymal deficiency of Notch1 attenuates bleomycin-induced pulmonary fibrosis

Notch signaling pathway is involved in the regulation of cell fate, differentiation, proliferation, and apoptosis in development and disease. Previous studies suggest the importance of Notch1 in myofibroblast differentiation in lung alveogenesis and fibrosis. However, direct in vivo evidence of Notch1-mediated myofibroblast differentiation is lacking. In this study, we examined the effects of conditional mesenchymal-specific deletion of Notch1 on pulmonary fibrosis. Crossing of mice bearing the floxed Notch1 gene with α2(I) collagen enhancer-Cre-ER(T)-bearing mice successfully generated progeny with a conditional knockout (CKO) of Notch1 in collagen I-expressing (mesenchymal) cells on treatment with tamoxifen (Notch1 CKO). Because Notch signaling is known to be activated in the bleomycin model of pulmonary fibrosis, control and Notch1 CKO mice were analyzed for their responses to bleomycin treatment. The results showed significant attenuation of pulmonary fibrosis in CKO relative to control mice, as examined by collagen deposition, myofibroblast differentiation, and histopathology. However, there were no significant differences in inflammatory or immune cell influx between bleomycin-treated CKO and control mouse lungs. Analysis of isolated lung fibroblasts confirmed absence of Notch1 expression in cells from CKO mice, which contained fewer myofibroblasts and significantly diminished collagen I expression relative to those from control mice. These findings revealed an essential role for Notch1-mediated myofibroblast differentiation in the pathogenesis of pulmonary fibrosis.

Lung bone marrow-derived hematopoietic progenitor cells enhance pulmonary fibrosis

RATIONALE

Bone marrow (BM)-derived cells have been implicated in pulmonary fibrosis. However, their precise role in pathogenesis is incompletely understood.

OBJECTIVES

To elucidate roles of BM-derived cells in bleomycin-induced pulmonary fibrosis, and clarify their potential relationship to lung hematopoietic progenitor cells (LHPCs).

METHODS

GFP BM-chimera mice treated with or without bleomycin were used to assess the BM-derived cells.

MEASUREMENTS AND MAIN RESULTS

GFP(+) cells in the chimera lung were found to be comprised of two distinct phenotypes: GFP(hi) and GFP(low) cells. The GFP(hi), but not GFP(low), population was significantly increased after bleomycin treatment. Flow-cytometric analysis and quantitative real-time polymerase chain reaction revealed that GFP(hi) cells exhibited phenotypic characteristics of CD11c(+) dendritic cells and macrophages. GFP(hi) cell conditioned media were chemotactic for fibroblasts obtained from fibrotic but not normal lung in vitro. Moreover, adoptive transfer of GFP(hi) cells exacerbated fibrosis in recipient mice, similar to that seen on adoptive transfer of BM-derived CD11c(+) cells from donor bleomycin-treated mice. Next, we evaluated the potential of LHPCs as the source of GFP(hi) cells. Isolation of LHPCs by flow sorting revealed enrichment in cKit(+)/Sca1(-)/Lin(-) cells, most of which were GFP(+) indicating their BM origin. The number of LHPCs increased rapidly after bleomycin treatment. Furthermore, stem cell factor induced LHPC proliferation, whereas granulocyte-macrophage-colony stimulating factor induced differentiation to GFP(hi) cells.

CONCLUSIONS

BM-derived LHPCs with a novel phenotype could differentiate into GFP(hi) cells, which enhanced pulmonary fibrosis. Targeting this mobilized LHPCs might represent a novel therapeutic approach in chronic fibrotic lung diseases.

Type V collagen induced tolerance suppresses collagen deposition, TGF-β and associated transcripts in pulmonary fibrosis

RATIONALE

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease characterized by progressive scarring and matrix deposition. Recent reports highlight an autoimmune component in IPF pathogenesis. We have reported anti-col(V) immunity in IPF patients. The objective of our study was to determine the specificity of col(V) expression profile and anti-col(V) immunity relative to col(I) in clinical IPF and the efficacy of nebulized col(V) in pre-clinical IPF models.

METHODS

Col(V) and col(I) expression profile was analyzed in normal human and IPF tissues. C57-BL6 mice were intratracheally instilled with bleomycin (0.025 U) followed by col(V) nebulization at pre-/post-fibrotic stage and analyzed for systemic and local responses.

RESULTS

Compared to normal lungs, IPF lungs had higher protein and transcript expression of the alpha 1 chain of col(V) and col(I). Systemic anti-col(V) antibody concentrations, but not of anti-col(I), were higher in IPF patients. Nebulized col(V), but not col(I), prevented bleomycin-induced fibrosis, collagen deposition, and myofibroblast differentiation. Col(V) treatment suppressed systemic levels of anti-col(V) antibodies, IL-6 and TNF-α; and local Il-17a transcripts. Compared to controls, nebulized col(V)-induced tolerance abrogated antigen-specific proliferation in mediastinal lymphocytes and production of IL-17A, IL-6, TNF-α and IFN-γ. In a clinically relevant established fibrosis model, nebulized col(V) decreased collagen deposition. mRNA array revealed downregulation of genes specific to fibrosis (Tgf-β, Il-1β, Pdgfb), matrix (Acta2, Col1a2, Col3a1, Lox, Itgb1/6, Itga2/3) and members of the TGF-β superfamily (Tgfbr1/2, Smad2/3, Ltbp1, Serpine1, Nfkb/Sp1/Cebpb).

CONCLUSIONS

Anti-col(V) immunity is pathogenic in IPF, and col(V)-induced tolerance abrogates bleomycin-induced fibrogenesis and down regulates TGF- β-related signaling pathways.

Myofibroblasts

PURPOSE OF REVIEW

Interest in the myofibroblast as a key player in propagation of chronic progressive fibrosis continues to elicit many publications, with focus on its cellular origins and the mechanisms underpinning their differentiation and/or transition. The objective of the review is to highlight this recent progress.

RECENT FINDINGS

The epithelial origin of the myofibroblast in fibrosis has been challenged by recent studies, with the pericyte suggested as a possible precursor instead. Additional signaling pathways, including Notch, Wnt, and hedgehog, are implicated in myofibroblast differentiation. The importance of NADPH oxidase 4 was highlighted recently to suggest a potential link between cellular/oxidative stress and the genesis of the myofibroblast. Recent observations on the importance of lysophosphatidic acid in fibrosis suggest that this may be due, in part, to its ability to regulate myofibroblast differentiation. Finally, there is increasing evidence for the role of epigenetic mechanisms in regulating myofibroblast differentiation, including DNA methylation and miRNA regulation of gene expression.

SUMMARY

These recent discoveries open up a whole new array of potential targets for novel antifibrotic therapies. This is of special importance given the current bleak outlook for chronic progressive fibrotic diseases, such as scleroderma, due to lack of effective therapies.