Progressive Transforming Growth Factor β1–induced Lung Fibrosis Is Blocked by an Orally Active ALK5 Kinase Inhibitor

[Targeting the TGF-β pathway in pulmonary fibrosis: Is it still a relevant strategy?]

Idiopathic pulmonary fibrosis (IPF) is a rare, progressive and fatal disease without pharmacologic curative treatments for the patients. TGF-β is a crucial cytokine in the fibrotic process, and its intracellular signaling pathways are complex and rely on the activation of its receptor. This review summarizes our knowledge on the regulatory checkpoints of the TGF-β signaling. In addition, the main strategies and key potential therapeutic targets identified over recent years are presented, with particular emphasis laid on how they can be used to develop new treatments for pulmonary fibrosis.

Quantitative Assessment of Pulmonary Fibrosis in a Murine Model via a Multimodal Imaging Workflow

Disease-recapitulating animal models are valuable tools in preclinical development for the study of compounds. In the case of fibrotic pulmonary diseases such as idiopathic pulmonary fibrosis (IPF), the bleomycin model of lung injury in the mouse is widely used. To evaluate bleomycin-induced changes in the lung, we employed a quantitative, multimodal approach. Using in vivo microcomputed tomography (μCT), we demonstrated radiographic changes associated with disease progression in aeration levels of the lung parenchyma. There exists an unmet need for a quantitative, high-resolution imaging probe to detect pulmonary fibrosis, particularly that can differentiate between inflammatory and fibrotic components of the disease. Matrix remodeling and overexpression of extracellular matrix (ECM) proteins such as collagen and fibronectin are hallmarks of organ fibrosis. A splice variant of fibronectin containing extra domain A (FnEDA) is of particular interest in fibrosis due to its high level of expression in diseased tissue, which is confirmed here using immunohistochemistry (IHC) in mouse and human lungs. An antibody against FnEDA was evaluated for use as an imaging tool, particularly by using in vivo single-photon emission computed tomography (SPECT) and ex vivo near-infrared (NIR) fluorescence imaging. These data were further corroborated with histological tissue staining and fibrosis quantitation based on a Modified Ashcroft (MA) score and a digital image analysis of whole slide lung tissue sections. The fusion of these different approaches represents a robust integrated workflow combining anatomical and molecular imaging technologies to enable the visualization and quantitation of disease activity and treatment response with an inhibitor of the TGFβ signaling pathway.

Pharmacotherapy of Liver Fibrosis and Hepatitis: Recent Advances

Liver fibrosis is a progressive scarring process primarily caused by chronic inflammation and injury, often closely associated with viral hepatitis, alcoholic liver disease, metabolic dysfunction-associated steatotic liver disease (MASLD), drug-induced liver injury, and autoimmune liver disease (AILD). Currently, there are very few clinical antifibrotic drugs available, and effective targeted therapy is lacking. Recently, emerging antifibrotic drugs and immunomodulators have shown promising results in animal studies, and some have entered clinical research phases. This review aims to systematically review the molecular mechanisms underlying liver fibrosis, focusing on advancements in drug treatments for hepatic fibrosis. Furthermore, since liver fibrosis is a progression or endpoint of many diseases, it is crucial to address the etiological treatment and secondary prevention for liver fibrosis. We will also review the pharmacological treatments available for common hepatitis leading to liver fibrosis.

Thioamides in medicinal chemistry and as small molecule therapeutic agents

Thioamides, which are fascinating isosteres of amides, have garnered significant attention in drug discovery and medicinal chemistry programs, spanning peptides and small molecule compounds. This review provides an overview of the various applications of thioamides in small molecule therapeutic agents targeting a range of human diseases, including cancer, microbial infections (e.g., tuberculosis, bacteria, and fungi), viral infections, neurodegenerative conditions, analgesia, and others. Particular focus is given to design strategies of biologically active thioamide-containing compounds and their biological targets, such as kinases and histone methyltransferase ASH1L. Additionally, the review discusses the impact of the thioamide moiety on key properties, including potency, target interactions, physicochemical characteristics, and pharmacokinetics profiles. We hope that this work will offer valuable insights to inspire the future development of novel bioactive thioamide-containing compounds, facilitating their effective use in combating a wide array of human diseases.

Advances in the discovery of activin receptor-like kinase 5 (ALK5) inhibitors

Activin receptor‑like kinase-5 (ALK5) is an outstanding member of the transforming growth factor-β (TGF-β) family. (TGF-β) signaling pathway integrates pleiotropic proteins that regulate various cellular processes such as growth, proliferation, and differentiation. Dysregulation within the signaling pathway can cause variety of diseases, such as fibrosis, cardiovascular disease, and especially cancer, rendering ALK5 a potential drug target. Hence, various small molecules have been designed and synthesized as potent ALK5 inhibitors. In this review, we shed light on the current ATP-competitive inhibitors of ALK5 through diverse heterocyclic based scaffolds that are in clinical or pre-clinical phases of development. Moreover, we focused on the binding interactions of the compounds to the ATP binding site and the structure-activity relationship (SAR) of each scaffold, revealing new scopes for designing novel candidates with enhanced selectivity and metabolic profiles.

A modest proposal: targeting αv integrin-mediated activation of latent TGFbeta as a novel therapeutic approach to treat scleroderma fibrosis

INTRODUCTION

The potent profibrotic cytokine transforming growth factor-β (TGF-β) has been associated with the onset and progression of the fibrosis seen in the autoimmune connective tissue disease scleroderma (systemic sclerosis, SSc).

AREA COVERED

This review explores the data supporting the notion that TGF-β contributes to SSc fibrosis and examines why initiating clinical trials in SSc aimed at targeting integrin-mediated latent TGF-β activation is timely.

EXPERT OPINION

Targeting TGF-β directly has not been proven to be clinically effective in this disease. Conversely, targeting matrix stiffness, which perpetuates fibrosis, may have more promise. Intriguingly, targeting integrin-mediated activation of latent TGF-β, which bridges these concepts, may have therapeutic value.

An agent-based modeling approach for lung fibrosis in response to COVID-19

The severity of the COVID-19 pandemic has created an emerging need to investigate the long-term effects of infection on patients. Many individuals are at risk of suffering pulmonary fibrosis due to the pathogenesis of lung injury and impairment in the healing mechanism. Fibroblasts are the central mediators of extracellular matrix (ECM) deposition during tissue regeneration, regulated by anti-inflammatory cytokines including transforming growth factor beta (TGF-β). The TGF-β-dependent accumulation of fibroblasts at the damaged site and excess fibrillar collagen deposition lead to fibrosis. We developed an open-source, multiscale tissue simulator to investigate the role of TGF-β sources in the progression of lung fibrosis after SARS-CoV-2 exposure, intracellular viral replication, infection of epithelial cells, and host immune response. Using the model, we predicted the dynamics of fibroblasts, TGF-β, and collagen deposition for 15 days post-infection in virtual lung tissue. Our results showed variation in collagen area fractions between 2% and 40% depending on the spatial behavior of the sources (stationary or mobile), the rate of activation of TGF-β, and the duration of TGF-β sources. We identified M2 macrophages as primary contributors to higher collagen area fraction. Our simulation results also predicted fibrotic outcomes even with lower collagen area fraction when spatially-localized latent TGF-β sources were active for longer times. We validated our model by comparing simulated dynamics for TGF-β, collagen area fraction, and macrophage cell population with independent experimental data from mouse models. Our results showed that partial removal of TGF-β sources changed the fibrotic patterns; in the presence of persistent TGF-β sources, partial removal of TGF-β from the ECM significantly increased collagen area fraction due to maintenance of chemotactic gradients driving fibroblast movement. The computational findings are consistent with independent experimental and clinical observations of collagen area fractions and cell population dynamics not used in developing the model. These critical insights into the activity of TGF-β sources may find applications in the current clinical trials targeting TGF-β for the resolution of lung fibrosis.

An agent-based modeling approach for lung fibrosis in response to COVID-19

The severity of the COVID-19 pandemic has created an emerging need to investigate the long-term effects of infection on patients. Many individuals are at risk of suffering pulmonary fibrosis due to the pathogenesis of lung injury and impairment in the healing mechanism. Fibroblasts are the central mediators of extracellular matrix (ECM) deposition during tissue regeneration, regulated by anti-inflammatory cytokines including transforming growth factor beta (TGF-β). The TGF-β-dependent accumulation of fibroblasts at the damaged site and excess fibrillar collagen deposition lead to fibrosis. We developed an open-source, multiscale tissue simulator to investigate the role of TGF-β sources in the progression of lung fibrosis after SARS-CoV-2 exposure, intracellular viral replication, infection of epithelial cells, and host immune response. Using the model, we predicted the dynamics of fibroblasts, TGF-β, and collagen deposition for 15 days post-infection in virtual lung tissue. Our results showed variation in collagen area fractions between 2% and 40% depending on the spatial behavior of the sources (stationary or mobile), the rate of activation of TGF-β, and the duration of TGF-β sources. We identified M2 macrophages as primary contributors to higher collagen area fraction. Our simulation results also predicted fibrotic outcomes even with lower collagen area fraction when spatially-localized latent TGF-β sources were active for longer times. We validated our model by comparing simulated dynamics for TGF-β, collagen area fraction, and macrophage cell population with independent experimental data from mouse models. Our results showed that partial removal of TGF-β sources changed the fibrotic patterns; in the presence of persistent TGF-β sources, partial removal of TGF-β from the ECM significantly increased collagen area fraction due to maintenance of chemotactic gradients driving fibroblast movement. The computational findings are consistent with independent experimental and clinical observations of collagen area fractions and cell population dynamics not used in developing the model. These critical insights into the activity of TGF-β sources may find applications in the current clinical trials targeting TGF-β for the resolution of lung fibrosis.

Author summary

COVID-19 survivors are at risk of lung fibrosis as a long-term effect. Lung fibrosis is the excess deposition of tissue materials in the lung that hinder gas exchange and can collapse the whole organ. We identified TGF-β as a critical regulator of fibrosis. We built a model to investigate the mechanisms of TGF-β sources in the process of fibrosis. Our results showed spatial behavior of sources (stationary or mobile) and their activity (activation rate of TGF-β, longer activation of sources) could lead to lung fibrosis. Current clinical trials for fibrosis that target TGF-β need to consider TGF-β sources' spatial properties and activity to develop better treatment strategies.

The role of transforming growth factor-β2 in cigarette smoke-induced lung inflammation and injury

AIMS

Transforming growth factor-β2 (TGF-β2) plays an important role in pleiotropic functions and has been reported to be involved in the pathogenesis of chronic obstructive lung disease. The role of TGF-β2 in regulating cigarette smoke (CS)-induced lung inflammation and injury has not been investigated, and its underlying mechanism remains unclear.

MAIN METHODS

Primary bronchial epithelial cells (PBECs) were treated with cigarette smoke extract (CSE), and the signaling pathway of TGF-β2 regulating lung inflammation was investigated. Mice were exposed to CS and treated with TGF-β2 i.p. or bovine whey protein extract containing TGF-β2 p.o., and the role of TGF-β2 in alleviating lung inflammation/injury was studied.

KEY FINDINGS

In vitro, we demonstrated that TGF-β2 attenuated CSE-induced IL-8 production from PBECs through the TGF-β receptor I (TGF-βRI), Smad3, and mitogen-activated protein kinase signaling pathways. Selective TGF-βRI inhibitor (LY364947) and antagonist of Smad3 (SIS3) abolished the effect of TGF-β2 on alleviating CSE-induced IL-8 production. In vivo, CS exposure for 4 weeks in mice increased the levels of total protein, inflammatory cell counts, and monocyte chemoattractant protein-1 in bronchoalveolar fluid and induced lung inflammation/injury, as revealed by immunohistochemistry. Administration of TGF-β2 through intraperitoneal injection or oral feeding with bovine whey protein extract containing TGF-β2 significantly reduced CS-induced lung inflammation and injury.

SIGNIFICANCE

We concluded that TGF-β2 reduced CSE-induced IL-8 production through the Smad3 signaling pathway in PBECs and alleviated lung inflammation/injury in CS-exposed mice. The anti-inflammatory effect of TGF-β2 on CS-induced lung inflammation in humans deserves further clinical study.

Indocyanine-enhanced mouse model of bleomycin-induced lung fibrosis with hallmarks of progressive emphysema

The development of new drugs for idiopathic pulmonary fibrosis strongly relies on preclinical experimentation, which requires the continuous improvement of animal models and integration with in vivo imaging data. Here, we investigated the lung distribution of bleomycin (BLM) associated with the indocyanine green (ICG) dye by fluorescence imaging. A long-lasting lung retention (up to 21 days) was observed upon oropharyngeal aspiration (OA) of either ICG or BLM + ICG, with significantly more severe pulmonary fibrosis, accompanied by the progressive appearance of emphysema-like features, uniquely associated with the latter combination. More severe and persistent lung fibrosis, together with a progressive air space enlargement uniquely associated with the BLM + ICG group, was confirmed by longitudinal micro-computed tomography (CT) and histological analyses. Multiple inflammation and fibrosis biomarkers were found to be increased in the bronchoalveolar lavage fluid of BLM- and BLM + ICG-treated animals, but with a clear trend toward a much stronger increase in the latter group. Similarly, in vitro assays performed on macrophage and epithelial cell lines revealed a significantly more marked cytotoxicity in the case of BLM + ICG-treated mice. Also unique to this group was the synergistic upregulation of apoptotic markers both in lung sections and cell lines. Although the exact mechanism underlying the more intense lung fibrosis phenotype with emphysema-like features induced by BLM + ICG remains to be elucidated, we believe that this combination treatment, whose overall effects more closely resemble the human disease, represents a valuable alternative model for studying fibrosis development and for the identification of new antifibrotic compounds.

Thrombo-Inflammation in COVID-19 and Sickle Cell Disease: Two Faces of the Same Coin

People with sickle cell disease (SCD) are at greater risk of severe illness and death from respiratory infections, including COVID-19, than people without SCD (Centers for Disease Control and Prevention, USA). Vaso-occlusive crises (VOC) in SCD and severe SARS-CoV-2 infection are both characterized by thrombo-inflammation mediated by endothelial injury, complement activation, inflammatory lipid storm, platelet activation, platelet-leukocyte adhesion, and activation of the coagulation cascade. Notably, lipid mediators, including thromboxane A2, significantly increase in severe COVID-19 and SCD. In addition, the release of thromboxane A2 from endothelial cells and macrophages stimulates platelets to release microvesicles, which are harbingers of multicellular adhesion and thrombo-inflammation. Currently, there are limited therapeutic strategies targeting platelet-neutrophil activation and thrombo-inflammation in either SCD or COVID-19 during acute crisis. However, due to many similarities between the pathobiology of thrombo-inflammation in SCD and COVID-19, therapies targeting one disease may likely be effective in the other. Therefore, the preclinical and clinical research spurred by the COVID-19 pandemic, including clinical trials of anti-thrombotic agents, are potentially applicable to VOC. Here, we first outline the parallels between SCD and COVID-19; second, review the role of lipid mediators in the pathogenesis of these diseases; and lastly, examine the therapeutic targets and potential treatments for the two diseases.

Increased expression and accumulation of GDF15 in IPF extracellular matrix contribute to fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic disease of unmet medical need. It is characterized by formation of scar tissue leading to a progressive and irreversible decline in lung function. IPF is associated with repeated injury, which may alter the composition of the extracellular matrix (ECM). Here, we demonstrate that IPF patient–derived pulmonary ECM drives profibrotic response in normal human lung fibroblasts (NHLF) in a 3D spheroid assay. Next, we reveal distinct alterations in composition of the diseased ECM, identifying potentially novel associations with IPF. Growth differentiation factor 15 (GDF15) was identified among the most significantly upregulated proteins in the IPF lung–derived ECM. In vivo, GDF15 neutralization in a bleomycin-induced lung fibrosis model led to significantly less fibrosis. In vitro, recombinant GDF15 (rGDF15) stimulated α smooth muscle actin (αSMA) expression in NHLF, and this was mediated by the activin receptor-like kinase 5 (ALK5) receptor. Furthermore, in the presence of rGDF15, the migration of NHLF in collagen gel was reduced. In addition, we observed a cell type–dependent effect of GDF15 on the expression of cell senescence markers. Our data suggest that GDF15 mediates lung fibrosis through fibroblast activation and differentiation, implicating a potential direct role of this matrix-associated cytokine in promoting aberrant cell responses in disease.

Extracellular Lipids in the Lung and Their Role in Pulmonary Fibrosis

Lipids are major actors and regulators of physiological processes within the lung. Initial research has described their critical role in tissue homeostasis and in orchestrating cellular communication to allow respiration. Over the past decades, a growing body of research has also emphasized how lipids and their metabolism may be altered, contributing to the development and progression of chronic lung diseases such as pulmonary fibrosis. In this review, we first describe the current working model of the mechanisms of lung fibrogenesis before introducing lipids and their cellular metabolism. We then summarize the evidence of altered lipid homeostasis during pulmonary fibrosis, focusing on their extracellular forms. Finally, we highlight how lipid targeting may open avenues to develop therapeutic options for patients with lung fibrosis.

Lung-restricted ALK5 inhibition avoids systemic toxicities associated with TGFβ pathway inhibition

Systemic therapies targeting transforming growth factor beta (TGFβ) or TGFβR1 kinase (ALK5) have been plagued by toxicities including cardiac valvulopathy and bone physeal dysplasia in animals, posing a significant challenge for clinical development in pulmonary indications. The current work aims to demonstrate that systemic ALK5-associated toxicities can be mitigated through localized lung delivery. Lung-selective (THRX-144644) and systemically bioavailable (galunisertib) ALK5 inhibitors were compared to determine whether lung selectivity is sufficient to maintain local tissue concentrations while mitigating systemic exposure and consequent pathway-related findings. Both molecules demonstrated potent ALK5 activity in rat precision cut lung slices (PCLS; p-SMAD3 half-maximal inhibitory concentration [IC50], 141 nM and 1070 nM for THRX-144644 and galunisertib, respectively). In 14-day repeat-dose studies in rats, dose-related cardiac valvulopathy was recapitulated with oral galunisertib at doses ≥150 mg/kg/day. In contrast, inhaled nebulized THRX-144644 did not cause similar systemic findings up to the maximally tolerated doses in rats or dogs (10 and 1.5 mg/kg/day, respectively). THRX-144644 lung-to-plasma ratios ranged from 100- to 1200-fold in rats and dogs across dose levels. THRX-144644 lung trough (24 h) concentrations in rats and dogs ranged from 3- to 17-fold above the PCLS IC50 across tolerated doses. At a dose level exceeding tolerability (60 mg/kg/day; 76-fold above PCLS IC50) minimal heart and bone changes were observed when systemic drug concentrations reached pharmacologic levels. In conclusion, the current preclinical work demonstrates that localized pulmonary delivery of an ALK5 inhibitor leads to favorable TGFβ pathway pharmacodynamic inhibition in lung while minimizing key systemic toxicities.

A Tight Control of Non-Canonical TGF-β Pathways and MicroRNAs Downregulates Nephronectin in Podocytes

Nephronectin (NPNT) is an extracellular matrix protein in the glomerular basement membrane that is produced by podocytes and is important for the integrity of the glomerular filtration barrier. Upregulated transforming growth factor β (TGF-β) and altered NPNT are seen in different glomerular diseases. TGF-β downregulates NPNT and upregulates NPNT-targeting microRNAs (miRs). However, the pathways involved were previously unknown. By using selective inhibitors of the canonical, SMAD-dependent, and non-canonical TGF-β pathways, we investigated NPNT transcription, translation, secretion, and regulation through miRs in podocytes. TGF-β decreased NPNT mRNA and protein in cultured human podocytes. TGF-β-dependent regulation of NPNT was meditated through intracellular signaling pathways. Under baseline conditions, non-canonical pathways predominantly regulated NPNT post-transcriptionally. Podocyte NPNT secretion, however, was not dependent on canonical or non-canonical TGF-β pathways. The canonical TGF-β pathway was also dispensable for NPNT regulation after TGF-β stimulation, as TGF-β was still able to downregulate NPNT in the presence of SMAD inhibitors. In contrast, in the presence of different non-canonical pathway inhibitors, TGF-β stimulation did not further decrease NPNT expression. Moreover, distinct non-canonical TGF-β pathways mediated TGF-β-induced upregulation of NPNT-targeting miR-378a-3p. Thus, we conclude that post-transcriptional fine-tuning of NPNT expression in podocytes is mediated predominantly through non-canonical TGF-β pathways.

Ramatroban for chemoprophylaxis and treatment of COVID-19: David takes on Goliath

INTRODUCTION

In COVID-19 pneumonia, there is a massive increase in fatty acid levels and lipid mediators with a predominance of cyclooxygenase metabolites, notably TxB2 ≫ PGE2 > PGD2 in the lungs, and 11-dehydro-TxB2, a TxA2 metabolite, in the systemic circulation. While TxA2 stimulates thromboxane prostanoid (TP) receptors, 11-dehydro-TxB2 is a full agonist of DP2 (formerly known as the CRTh2) receptors for PGD2. Anecdotal experience of using ramatroban, a dual receptor antagonist of the TxA2/TP and PGD2/DP2 receptors, demonstrated rapid symptomatic relief from acute respiratory distress and hypoxemia while avoiding hospitalization.

AREAS COVERED

Evidence supporting the role of TxA2/TP receptors and PGD2/DP2 receptors in causing rapidly progressive lung injury associated with hypoxemia, a maladaptive immune response and thromboinflammation is discussed. An innovative perspective on the dual antagonism of TxA2/TP and PGD2/DP2 receptor signaling as a therapeutic approach in COVID-19 is presented. This paper examines ramatroban an anti-platelet, immunomodulator, and antifibrotic agent for acute and long-haul COVID-19.

EXPERT OPINION

Ramatroban, a dual blocker of TP and DP2 receptors, has demonstrated efficacy in animal models of respiratory dysfunction, atherosclerosis, thrombosis, and sepsis, as well as preliminary evidence for rapid relief from dyspnea and hypoxemia in COVID-19 pneumonia. Ramatroban merits investigation as a promising antithrombotic and immunomodulatory agent for chemoprophylaxis and treatment.

Interleukin-1 receptor antagonist inhibits arthrofibrosis in a post-traumatic knee immobilization model

BACKGROUND

Therapies for arthrofibrosis after knee surgery are needed to prevent loss of joint function. Interleukin-1 receptor antagonists (IL-1RA) have shown promise in treating established arthrofibrosis in pilot clinical studies. The objective of this study was to evaluate the ability of intra-articular injection of IL-1RA to prevent knee joint contracture in a post-traumatic knee immobilization model.

METHODS

20 male Sprague Dawley rats were block randomized into two groups: control and IL-1RA. Rats underwent intra-articular surgical trauma of the right knee with placement of an immobilization suture, securing the knees in 150° flexion. On post-operative days 1 and 8, each group received a 0.1 ml intra-articular injection of either saline (control) or anakinra (IL-1RA:single dosage; 2.63 mg/kg). Rats were euthanized fourteen days after surgery and the immobilization femorotibial angles were measured on the operative limbs with the suture and musculature intact. Subsequently, musculature was removed and femorotibial angles were measured in the operative and non-operative limbs with a defined extension moment applied with the posterior capsule intact or cut. A contracture angle was calculated as the angular difference between the operative and non-operative limb.

RESULTS

The immobilization knee flexion angle did not differ (P = 0.761) between groups (control: 152 ± 9; IL-1RA: 150 ± 11). The joint contracture angles (smaller angle = improved outcome) were reduced by 12 degrees on average in the IL-1RA group compared to the control for both the capsule intact (P = 0.024) and cut (P = 0.019) states.

CONCLUSIONS

Intra-articular IL-1RA injection was found to diminish knee extension deficits associated with arthrofibrosis in a post-traumatic joint immobilization model.

Gremlin2 Activates Fibroblasts to Promote Pulmonary Fibrosis Through the Bone Morphogenic Protein Pathway

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease causing unremitting extracellular matrix deposition. Transforming growth factor-β (TGF-β) superfamily involves bone morphogenetic proteins (BMPs) and TGF-β, and the balance between the activation of TGF-β-dependent SMADs (Smad2/3) and BMP-dependent SMADs (Smad1/5/8) is essential for fibrosis process. GREM2, initially identified as a TGF-β-inducible gene, encodes a small secreted glycoprotein belonging to a group of matricellular proteins, its role in lung fibrosis is not clear. Here, we identified Gremlin2 as a key regulator of fibroblast activation. Gremlin2 was highly expressed in the serum and lung tissues in IPF patients. Bleomycin-induced lung fibrosis model exhibited high expression of Gremlin2 in the bronchoalveolar lavage fluid (BALF) and lung tissue. Isolation of primary cells from bleomycin-induced fibrosis lung showed a good correlation of Gremlin2 and Acta2 (α-SMA) expressions. Overexpression of Gremlin2 in human fetal lung fibroblast 1 (HFL-1) cells increased its invasion and migration. Furthermore, Gremlin2 regulates fibrosis functions through mediating TGF-β/BMP signaling, in which Gremlin2 may activate TGF-β signaling and inhibit BMP signaling. Therefore, we provided in vivo and in vitro evidence to demonstrate that Gremlin2 may be a potential therapeutic target for the treatment of IPF.

COVID-19 and pulmonary fibrosis: A potential role for lung epithelial cells and fibroblasts

The COVID-19 pandemic rapidly spread around the world following the first reports in Wuhan City, China in late 2019. The disease, caused by the novel SARS-CoV-2 virus, is primarily a respiratory condition that can affect numerous other bodily systems including the cardiovascular and gastrointestinal systems. The disease ranges in severity from asymptomatic through to severe acute respiratory distress requiring intensive care treatment and mechanical ventilation, which can lead to respiratory failure and death. It has rapidly become evident that COVID-19 patients can develop features of interstitial pulmonary fibrosis, which in many cases persist for as long as we have thus far been able to follow the patients. Many questions remain about how such fibrotic changes occur within the lung of COVID-19 patients, whether the changes will persist long term or are capable of resolving, and whether post-COVID-19 pulmonary fibrosis has the potential to become progressive, as in other fibrotic lung diseases. This review brings together our existing knowledge on both COVID-19 and pulmonary fibrosis, with a particular focus on lung epithelial cells and fibroblasts, in order to discuss common pathways and processes that may be implicated as we try to answer these important questions in the months and years to come.

Cobalt exposure increases the risk of fibrosis of people living near E‑waste recycling area

The toxicity of heavy metals is one of the major public health issues leading to hazardous effects on humans. Many studies focus on the adverse effects on people who were working in or living near E-waste recycling. However, little is known to the sustaining effects of E-waste exposure on human health after the recycling factories were shut down. In the present study, we collected the blood of people living near E‑waste recycling facilities after the recycling factories were closed for 2 years. Eight heavy metals were examined in all blood samples. The results revealed that the blood levels of lead (Pb), nickel (Ni), cobalt (Co), mercury (Hg) were significantly higher in the exposed group than in the reference group, and no difference was observed for copper (Cu), zinc (Zn), stannum (Sn), cadmium (Cd). Transforming growth factor-β (TGF-β) and alpha-smooth muscle actin (α-SMA) were analyzed as the important indicators of fibrosis, which were statistically significantly higher in the exposed group than in the reference group. 8-isoprostane (8-I) and malondialdehyde (MDA) as the biomarkers of oxidative stress (OS) were elevated in the exposed group. Furthermore, both Spearman correlation and multiple linear regression showed that Co was positively correlated with TGF-β, α-SMA and 8-I in the exposed group. Accordingly, we speculate that high concentrations of Co dissolved in the blood may increase the risk of tissue fibrosis through stimulating myofibroblast activation and OS involve in the process, which may provide some potential new hints for the intervention for tissue fibrosis in the future.

TGF-β as a driver of fibrosis: physiological roles and therapeutic opportunities

Many chronic diseases are marked by fibrosis, which is defined by an abundance of activated fibroblasts and excessive deposition of extracellular matrix, resulting in loss of normal function of the affected organs. The initiation and progression of fibrosis are elaborated by pro-fibrotic cytokines, the most critical of which is transforming growth factor-β1 (TGF-β1). This review focuses on the fibrogenic roles of increased TGF-β activities and underlying signaling mechanisms in the activated fibroblast population and other cell types that contribute to progression of fibrosis. Insight into these roles and mechanisms of TGF-β as a universal driver of fibrosis has stimulated the development of therapeutic interventions to attenuate fibrosis progression, based on interference with TGF-β signaling. Their promise in preclinical and clinical settings will be discussed. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Granulation tissue myofibroblasts during normal and pathological skin healing: The interaction between their secretome and the microenvironment

The first role that was proposed for the myofibroblasts located in skin granulation tissue was to contract the edges of the wound in order to reduce the surface to be repaired. This role, linked to the presence of alpha smooth muscle actin, was very quickly confirmed and is part of the definition of granulation tissue myofibroblasts. However, myofibroblasts are cells that also play a much more central role in wound healing. Indeed, it has been shown that these cells produce large quantities of matrix components, and that they stimulate angiogenesis and can recruit immune cells. These actions take place via the secretion of molecules into their environment or indirectly via the production of microvesicles containing pro-fibrotic and pro-angiogenic molecules. Pathologically, granulation tissue can develop into a hypertrophic scar that histologically looks like granulation tissue, but which can remain for months or even years. It has been hypothesized that the myofibroblasts in these tissues remained present instead of disappearing by apoptosis, causing the maintenance of granulation tissue rather than allowing its change into a mature scar. Understanding the roles of both pathological and healthy myofibroblasts in wound tissue is crucial in order to better intervene in the healing mechanism.

Protective and anti-inflammatory effect of selenium nano-particles against bleomycin-induced pulmonary injury in male rats

Pulmonary fibrosis (PF) is an interstitial lung disease, in which the exact pathologic mechanisms are not fully understood. Drug trials for the treatment of PF have shown disappointing results and controversial. Recently, selenium nanoparticles (SeNPs) have received great attention for potential use in treatments, due to high bioactivity features and lower toxicity. This study evaluated the protective effect of SeNPs against pulmonary injury induced by bleomycin (single dose, 4 mg/kg, intratracheal) in male rats in early and late phases of the disease. The rats were treated with SeNPs by intraperitoneal injection (0.5 mg SeNP/kg) for five consecutive days in the early phase (a day after injection of bleomycin) and late phase (a week after injection of bleomycin). The results showed that injection of SeNPs in the early phase improved the degree of alveolitis and inflammation and lung structure damage. Also, led to significant decreases in density of transforming growth factor- β1 (TGF-β1) in the lung and tumor necrosis factor-α (TNF-α) levels in the serum and lung homogenates compared with bleomycin-administrated group. Notably, treatment with the SeNP during the late phase did not show any ameliorative effects. Thus, the data suggest that SeNP has a protective effect against bleomycin-induced pulmonary injury in rats in the early phase of the disease. This might mean that SeNPs may be a new therapeutic agent for the improvement of this disease in the early phases.

The self-fulfilling prophecy of pulmonary fibrosis: a selective inspection of pathological signalling loops

Pulmonary fibrosis is a devastating, progressive disease and carries a prognosis worse than most cancers. Despite ongoing research, the mechanisms that underlie disease pathogenesis remain only partially understood. However, the self-perpetuating nature of pulmonary fibrosis has led several researchers to propose the existence of pathological signalling loops. According to this hypothesis, the normal wound-healing process becomes corrupted and results in the progressive accumulation of scar tissue in the lung. In addition, several negative regulators of pulmonary fibrosis are downregulated and, therefore, are no longer capable of inhibiting these feed-forward loops. The combination of pathological signalling loops and loss of a checks and balances system ultimately culminates in a process of unregulated scar formation. This review details specific signalling pathways demonstrated to play a role in the pathogenesis of pulmonary fibrosis. The evidence of detrimental signalling loops is elucidated with regard to epithelial cell injury, cellular senescence and the activation of developmental and ageing pathways. We demonstrate where these loops intersect each other, as well as common mediators that may drive these responses and how the loss of pro-resolving mediators may contribute to the propagation of disease. By focusing on the overlapping signalling mediators among the many pro-fibrotic pathways, it is our hope that the pulmonary fibrosis community will be better equipped to design future trials that incorporate the redundant nature of these pathways as we move towards finding a cure for this unrelenting disease.

Crosstalk between pleural mesothelial cell and lung fibroblast contributes to pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a specific form of chronic, progressive and fibrosing interstitial pneumonia of unknown cause. The main feature of IPF is a heterogeneous appearance with areas of sub-pleural fibrosis. However, the mechanism of sub-pleural fibrosis was poorly understood. In this study, our in vivo study revealed that pleural mesothelial cells (PMCs) migrated into lung parenchyma and localized alongside lung fibroblasts in sub-pleural area in mouse pulmonary fibrosis. Our in vitro study displayed that cultured-PMCs-medium induced lung fibroblasts transforming into myofibroblast, cultured-fibroblasts-medium promoted mesothelial-mesenchymal transition of PMCs. Furthermore, these changes in lung fibroblasts and PMCs were prevented by blocking TGF-β1/Smad2/3 signaling with SB431542. TGF-β1 neutralized antibody attenuated bleomycin-induced pulmonary fibrosis. Similar to TGF-β1/Smad2/3 signaling, wnt/β-catenin signaling was also activated in the process of PMCs crosstalk with lung fibroblasts. Moreover, inhibition of CD147 attenuated cultured-PMCs-medium induced collagen-I synthesis in lung fibroblasts. Blocking CD147 signaling also prevented bleomycin-induced pulmonary fibrosis. Our data indicated that crosstalk between PMC and lung fibroblast contributed to sub-pleural pulmonary fibrosis. TGF-β1, Wnt/β-catenin and CD147 signaling was involved in the underling mechanism.

Myricetin ameliorates bleomycin-induced pulmonary fibrosis in mice by inhibiting TGF-β signaling via targeting HSP90β

Idiopathic pulmonary fibrosis is a progressive-fibrosing lung disease with high mortality and limited therapy, which characterized by myofibroblasts proliferation and extracellular matrix deposition. Myricetin, a natural flavonoid, has been shown to possess a variety of biological characteristics including anti-inflammatory and anti-tumor. In this study we explored the potential effect and mechanisms of myricetin on pulmonary fibrosis in vivo and vitro. The in vivo studies showed that myricetin effectively alleviated bleomycin (BLM)-induced pulmonary fibrosis. KEGG analysis of RNA-seq data indicated that myricetin could regulate the transforming growth factor (TGF)-β signaling pathway. In vitro studies indicated that myricetin could dose-dependently suppress TGF-β1/Smad signaling and attenuate TGF-β1-induced fibroblast activation and epithelial-mesenchymal transition (EMT). Molecular docking indicated that heat shock protein (HSP) 90β may be a potential target of myricetin, and MST assay demonstrated that the dissociation constant (Kd) of myricetin and HSP90β was 331.59 nM. We demonstrated that myricetin interfered with the binding of HSP90β and TGF-β receptor II and impeded fibroblast activation and EMT. In conclusion, myricetin impedes TGF-β1-induced lung fibroblast activation and EMT via targeting HSP90β and attenuates BLM-induced pulmonary fibrosis in mice.

ALK5 deficiency inhibits macrophage inflammation and lipid loading by targeting KLF4

The transforming growth factor type-β (TGF-β) has been demonstrated to play an important role in the development of atherosclerosis through binding to the serine/threonine kinase transmembrane type I and type II receptors. However, as a key type I receptor for TGF-β, the exact role and the underlying mechanism of Activin receptor-like kinase 5 (ALK5) on macrophage activation involved in atherogenesis remain unclear. In the present study, enhanced ALK5 expression was found in bone marrow derived macrophages (BMDMs) upon OX-LDL stimulation tested by RT-PCR and Western blot, which was further verified by co-immunofluorescence staining. Next, the loss-of-function of ALK5 used AdshALK5 transfection was performed to test the effect of ALK5 on macrophage activation. We observed that ALK5 silencing inhibited pro-inflammatory but promoted anti-inflammatory macrophage markers expression. Moreover, decreased foam cell formation was found in ALK5 knockdown macrophages accompanied by increased cholesterol efflux. Mechanistically, ALK5 knockdown significantly increased KLF4 expression that was responsible for the attenuated macrophage activation induced by ALK5 knockdown. Collectively, these findings suggested that neutralization of ALK5 may act as a promising strategy for the management of atherosclerosis.

Development of small molecule inhibitors targeting TGF-β ligand and receptor: Structures, mechanism, preclinical studies and clinical usage

Transforming growth factor-β (TGF-β) is a member of a superfamily of pleiotropic proteins that regulate multiple cellular processes such as growth, development and differentiation. Following binding to type I and II TGF-β serine/threonine kinase receptors, TGF-β activates downstream signaling cascades involving both SMAD-dependent and -independent pathways. Aberrant TGF-β signaling is associated with a variety of diseases, such as fibrosis, cardiovascular disease and cancer. Hence, the TGF-β signaling pathway is recognized as a potential drug target. Various organic molecules have been designed and developed as TGF-β signaling pathway inhibitors and they function by either down-regulating the expression of TGF-β or by inhibiting the kinase activities of the TGF-β receptors. In this review, we discuss the current status of research regarding organic molecules as TGF-β inhibitors, focusing on the biological functions and the binding poses of compounds that are in the market or in the clinical or pre-clinical phases of development.

Transforming growth factor-β in tissue fibrosis

TGF-β is extensively implicated in the pathogenesis of fibrosis. In fibrotic lesions, spatially restricted generation of bioactive TGF-β from latent stores requires the cooperation of proteases, integrins, and specialized extracellular matrix molecules. Although fibroblasts are major targets of TGF-β, some fibrogenic actions may reflect activation of other cell types, including macrophages, epithelial cells, and vascular cells. TGF-β–driven fibrosis is mediated through Smad-dependent or non-Smad pathways and is modulated by coreceptors and by interacting networks. This review discusses the role of TGF-β in fibrosis, highlighting mechanisms of TGF-β activation and signaling, the cellular targets of TGF-β actions, and the challenges of therapeutic translation.

The circadian clock protein REVERBα inhibits pulmonary fibrosis development

Pulmonary inflammatory responses lie under circadian control; however, the importance of circadian mechanisms in the underlying fibrotic phenotype is not understood. Here, we identify a striking change to these mechanisms resulting in a gain of amplitude and lack of synchrony within pulmonary fibrotic tissue. These changes result from an infiltration of mesenchymal cells, an important cell type in the pathogenesis of pulmonary fibrosis. Mutation of the core clock protein REVERBα in these cells exacerbated the development of bleomycin-induced fibrosis, whereas mutation of REVERBα in club or myeloid cells had no effect on the bleomycin phenotype. Knockdown of REVERBα revealed regulation of the little-understood transcription factor TBPL1. Both REVERBα and TBPL1 altered integrinβ1 focal-adhesion formation, resulting in increased myofibroblast activation. The translational importance of our findings was established through analysis of 2 human cohorts. In the UK Biobank, circadian strain markers (sleep length, chronotype, and shift work) are associated with pulmonary fibrosis, making them risk factors. In a separate cohort, REVERBα expression was increased in human idiopathic pulmonary fibrosis (IPF) lung tissue. Pharmacological targeting of REVERBα inhibited myofibroblast activation in IPF fibroblasts and collagen secretion in organotypic cultures from IPF patients, thus suggesting that targeting of REVERBα could be a viable therapeutic approach.

Precision-cut lung slices from bleomycin treated animals as a model for testing potential therapies for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a complex lung disease with incompletely understood pathophysiology. Effectiveness of available medicines is limited and the need for new and improved therapies remains. Due to complexity of the disease, it is difficult to develop predictable in vitro models. In this study we have described precision-cut lung slices (PCLS) prepared from bleomycin treated mice as an in vitro model for testing of novel compounds with antifibrotic activity. We have shown that PCLS during in vitro incubation retain characteristics of bleomycin model with increased expression of fibrosis related genes ACTA2 (α-smooth muscle actin), COL1A1 (collagen 1), FN1 (fibronectin 1), MMP12 (matrix metalloproteinase 12) and TIMP1 (tissue inhibitor of metalloproteinases). To further evaluate PCLS as an in vitro model, we have tested ALK5 inhibitor SB525334 which was previously shown to attenuate fibrosis in in vivo bleomycin model and nintedanib which is the FDA approved treatment for IPF. SB525334 and nintedanib inhibited expression of fibrosis related genes in PCLS from bleomycin treated mice. In addition, comparable activity profile of SB525334 was achieved in PCLS and in vivo model. Altogether these results suggest that PCLS may be a suitable in vitro model for compound testing during drug development process.

Non-Canonical Regulation of Type I Collagen through Promoter Binding of SOX2 and Its Contribution to Ameliorating Pulmonary Fibrosis by Butylidenephthalide

Pulmonary fibrosis is a fatal respiratory disease that gradually leads to dyspnea, mainly accompanied by excessive collagen production in the fibroblast and myofibroblast through mechanisms such as abnormal alveolar epithelial cells remodeling and stimulation of the extracellular matrix (ECM). Our results show that a small molecule, butylidenephthalide (BP), reduces type I collagen (COL1) expression in Transforming Growth Factor beta (TGF-β)-induced lung fibroblast without altering downstream pathways of TGF-β, such as Smad phosphorylation. Treatment of BP also reduces the expression of transcription factor Sex Determining Region Y-box 2 (SOX2), and the ectopic expression of SOX2 overcomes the inhibitory actions of BP on COL1 expression. We also found that serial deletion of the SOX2 binding site on 3′COL1 promoter results in a marked reduction in luciferase activity. Moreover, chromatin immunoprecipitation, which was found on the SOX2 binding site of the COL1 promoter, decreases in BP-treated cells. In an in vivo study using a bleomycin-induced pulmonary fibrosis C57BL/6 mice model, mice treated with BP displayed reduced lung fibrosis and collagen deposition, recovering in their pulmonary ventilation function. The reduction of SOX2 expression in BP-treated lung tissues is consistent with our findings in the fibroblast. This is the first report that reveals a non-canonical regulation of COL1 promoter via SOX2 binding, and contributes to the amelioration of pulmonary fibrosis by BP treatment.

Synthesis and discovery of a drug candidate for treatment of idiopathic pulmonary fibrosis through inhibition of TGF-β1 pathway

In this study, anti-IPF lead compounds 42 and 44, derived from natural sesquiterpene lactones Isoalantolactone and alantolactone, were discovered by screening from a high-throughput TGF-β1 reporter luciferase assay. Notably, they could reduce the myofibroblast activation and extracellular matrix deposition both in vitro and in vivo. Additionally, compounds 42 and 44 could significantly attenuate bleomycin-induced pulmonary fibrosis in mice. Further validation of pharmacokinetics study and toxicity evaluation indicated that compound 44 might be a promising anti-IPF drug candidate.

Epithelial mesenchymal transition (EMT): a universal process in lung diseases with implications for cystic fibrosis pathophysiology

Cystic Fibrosis (CF) is a genetic disorder that arises due to mutations in the Cystic Fibrosis Transmembrane Conductance Regulator gene, which encodes for a protein responsible for ion transport out of epithelial cells. This leads to a disruption in transepithelial Cl-, Na + and HCO₃− ion transport and the subsequent dehydration of the airway epithelium, resulting in infection, inflammation and development of fibrotic tissue. Unlike in CF, fibrosis in other lung diseases including asthma, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis has been well characterised. One of the driving forces behind fibrosis is Epithelial Mesenchymal Transition (EMT), a process where epithelial cells lose epithelial proteins including E-Cadherin, which is responsible for tight junctions. The cell moves to a more mesenchymal phenotype as it gains mesenchymal markers such as N-Cadherin (providing the cells with migration potential), Vimentin and Fibronectin (proteins excreted to help form the extracellular matrix), and the fibroblast proliferation transcription factors Snail, Slug and Twist. This review paper explores the EMT process in a range of lung diseases, details the common links that these have to cystic fibrosis, and explores how understanding EMT in cystic fibrosis may open up novel methods of treating patients with cystic fibrosis.

Nanoscale dysregulation of collagen structure-function disrupts mechano-homeostasis and mediates pulmonary fibrosis

Matrix stiffening with downstream activation of mechanosensitive pathways is strongly implicated in progressive fibrosis; however, pathologic changes in extracellular matrix (ECM) that initiate mechano-homeostasis dysregulation are not defined in human disease. By integrated multiscale biomechanical and biological analyses of idiopathic pulmonary fibrosis lung tissue, we identify that increased tissue stiffness is a function of dysregulated post-translational collagen cross-linking rather than any collagen concentration increase whilst at the nanometre-scale collagen fibrils are structurally and functionally abnormal with increased stiffness, reduced swelling ratio, and reduced diameter. In ex vivo and animal models of lung fibrosis, dual inhibition of lysyl oxidase-like (LOXL) 2 and LOXL3 was sufficient to normalise collagen fibrillogenesis, reduce tissue stiffness, and improve lung function in vivo. Thus, in human fibrosis, altered collagen architecture is a key determinant of abnormal ECM structure-function, and inhibition of pyridinoline cross-linking can maintain mechano-homeostasis to limit the self-sustaining effects of ECM on progressive fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a devastating disease of the lung, which scars the tissue and gradually destroys the organ, ultimately leading to death. It is still unclear what exactly causes this scarring, but it is thought that increasing amounts of proteins in the space surrounding the cells of the lungs, the extracellular matrix, could play a role.

These proteins, including collagen, normally form a ‘scaffold’ to stabilize cells, but if they accumulate uncontrollably, they can render tissues rigid. It has been assumed that these changes are a consequence of the disease. However, recent evidence suggests that the increased stiffness itself could stimulate cells to produce even more extracellular matrix, driving the progression of the disease. A better understanding of what exactly causes the tissue to become gradually stiffer may identify new ways to block the progression of IPF.

Now, Jones et al. compared measurements of the tissue stiffness and the collagen structure taken from samples of patients with IPF. The results showed that the collagen fibres were faulty and had an abnormal shape. This suggests that these problems, rather than an increased amount of collagen, alter the flexibility of the lung tissue.

Jones et al. also found that a specific family of proteins, which helps to connect the collagen fibres, was increased in the tissue of patients with IPF. When these proteins were blocked with a newly developed drug, the collagen structure returned to normal and the stiffness of the tissue decreased. As a consequence, the lung capacity improved.

This suggests that treatment approaches that help to maintain a normal collagen structure, may in future prevent the stiffening of the lung tissue and so limit feed-forward mechanisms that drive progressive IPF. Moreover, it indicates that measurements of the structure of collagen rather than the its total concentration could serve as a more suitable indicator for the disease.

Experimental study on TGF-β1-mediated CD147 expression in oral submucous fibrosis

OBJECTIVE

Although previous evidence indicates that CD147 is closely involved in the progression of organ fibrosis and various signaling pathways have been proven to regulate its expression, the role of CD147 in oral submucous fibrosis (OSF) remains largely unknown.

METHODS

In this study, we investigated the expression of CD147 and transforming growth factor β1 (TGF-β1) in human samples of an OSF tissue array by immunohistopathology. Pearson's correlation analysis was conducted to explore the correlation between CD147 and TGF-β1. Immunofluorescence and Western blotting were used to investigate to levels of CD147 in Human Oral Keratinocytes (HOKs) followed by TGF-β1 or LY2157299, an inhibitor of TGF-β1 receptor and arecoline stimulation.

RESULTS

We found that CD147 was highly expressed in both HOKs and the fibrotic oral mucosa and that this expression was correlated with TGF-β1 expression. Additionally, CD147 levels were significantly associated with the fibrosis stage. The TGF-β1 signaling pathway was found to be mainly responsible for CD147 up-regulation after arecoline treatment whereas inhibition of TGF-β1 down-regulated CD147 expression.

CONCLUSION

Our findings suggest arecoline promotes CD147 expression via the TGF-β1 signaling pathway in HOKs, whereas overexpression of CD147 may promote OSF progression.

Networks of blood proteins in the neuroimmunology of schizophrenia

Levels of certain circulating cytokines and related immune system molecules are consistently altered in schizophrenia and related disorders. In addition to absolute analyte levels, we sought analytes in correlation networks that could be prognostic. We analyzed baseline blood plasma samples with a Luminex platform from 72 subjects meeting criteria for a psychosis clinical high-risk syndrome; 32 subjects converted to a diagnosis of psychotic disorder within two years while 40 other subjects did not. Another comparison group included 35 unaffected subjects. Assays of 141 analytes passed early quality control. We then used an unweighted co-expression network analysis to identify highly correlated modules in each group. Overall, there was a striking loss of network complexity going from unaffected subjects to nonconverters and thence to converters (applying standard, graph-theoretic metrics). Graph differences were largely driven by proteins regulating tissue remodeling (e.g. blood-brain barrier). In more detail, certain sets of antithetical proteins were highly correlated in unaffected subjects (e.g. SERPINE1 vs MMP9), as expected in homeostasis. However, for particular protein pairs this trend was reversed in converters (e.g. SERPINE1 vs TIMP1, being synthetical inhibitors of remodeling of extracellular matrix and vasculature). Thus, some correlation signals strongly predict impending conversion to a psychotic disorder and directly suggest pharmaceutical targets.

Negative regulation of TGF-β by AMPK and implications in the treatment of associated disorders

Transforming growth factor beta (TGF-β) regulates a large number of biological processes, including proliferation, differentiation, immune response, and development. In addition, TGF-β plays important roles in some pathological processes, for instance, it is upregulated and activated in fibrosis and advanced cancer. Adenosine monophosphate-activated protein kinase (AMPK) acts as a fuel gauge that is activated when cells sense shortage of ATP and increase in AMP or AMP:ATP ratio. Activation of AMPK slows down anabolic processes and stimulates catabolic processes, leading to increased production of ATP. Furthermore, the functions of AMPK have been extended beyond energy homeostasis. In fact, AMPK has been shown to exert a tumor suppressive effect. Recent studies have demonstrated negative impacts of AMPK on TGF-β function. Therefore, in this review, we will discuss the differences in the biological functions of TGF-β and AMPK, and some pathological processes such as fibrosis, epithelial-mesenchymal transition (EMT) and cancer metastasis, as well as angiogenesis and heterotopic ossifications where TGF-β and AMPK exert opposite effects.

Ubiquitination and deubiquitination emerge as players in idiopathic pulmonary fibrosis pathogenesis and treatment

Idiopathic pulmonary fibrosis (IPF) is a fatal fibrotic lung disease that is associated with aberrant activation of TGF-β, myofibroblast differentiation, and abnormal extracellular matrix (ECM) production. Proper regulation of protein stability is important for maintenance of intracellular protein homeostasis and signaling. Ubiquitin E3 ligases mediate protein ubiquitination, and deubiquitinating enzymes (DUBs) reverse the process. The role of ubiquitin E3 ligases and DUBs in the pathogenesis of IPF is relatively unexplored. In this review, we provide an overview of how ubiquitin E3 ligases and DUBs modulate pulmonary fibrosis through regulation of both TGF-β-dependent and -independent pathways. We also summarize currently available small-molecule inhibitors of ubiquitin E3 ligases and DUBs as potential therapeutic strategies for the treatment of IPF.

Therapeutic pro-fibrogenic signaling pathways in fibroblasts

Myofibroblasts (MFs) play a critical role in the progression of chronic inflammatory and fibroproliferative diseases in different tissues/organs, whatever the etiology. Fibrosis is preceded and sustained by persistent injury and inflammatory response in a profibrogenic scenario involving mutual interactions, operated by several mediators and pathways, of MFs and related precursor cells with innate immunity cells and virtually any cell type in a defined tissue. These interactions, mediators and related signaling pathways are critical in initiating and perpetuating the differentiation of precursor cells into MFs that in different tissues share peculiar traits and phenotypic responses, including the ability to proliferate, produce ECM components, migrate and contribute to the modulation of inflammatory response and tissue angiogenesis. Literature studies related to liver, lung and kidney fibrosis have outlined a number of MF-related core regulatory fibrogenic signaling pathways conserved across these different organs and potentially targetable in order to develop effective antifibrotic therapeutic strategies.

Reduction in skeletal muscle fibrosis of spontaneously hypertensive rats after laceration by microRNA targeting angiotensin II receptor

Regeneration of injured skeletal muscles is affected by fibrosis, which can be improved by the administration of angiotensin II (AngII) receptor (ATR) blockers in normotensive animals. However, the role of ATR in skeletal muscle fibrosis in hypertensive organisms has not been investigated yet. The tibialis anterior (TA) muscle of spontaneously hypertensive (SHR) and Wistar rats (WR) were lacerated and a lentivector encoding a microRNA targeting AngII receptor type 1 (At1) (Lv-mirAT1a) or control (Lv-mirCTL) was injected. The TA muscles were collected after 30 days to evaluate fibrosis by histology and gene expression by real-time quantitative PCR (RT-qPCR) and Western blot. SHR's myoblasts were analyzed by RT-qPCR, 48 h after transduction. In the SHR's TA, AT1 protein expression was 23.5-fold higher than in WR without injury, but no difference was observed in the angiotensin II receptor type 2 (AT2) protein expression. TA laceration followed by suture (LS) produced fibrosis in the SHR (23.3±8.5%) and WR (7.9±1.5%). Lv-mirAT1 treatment decreased At1 gene expression in 50% and reduced fibrosis to 7% 30 days after. RT-qPCR showed that reduction in At1 expression is due to downregulation of the At1a but not of the At1b. RT-qPCR of myoblasts from SHR transduced with Lv-mirAT1a showed downregulation of the Tgf-b1, Tgf-b2, Smad3, Col1a1, and Col3a1 genes by mirAT1a. In vivo and in vitro studies indicate that hypertension overproduces skeletal muscle fibrosis, and AngII-AT1a signaling is the main pathway of fibrosis in SHR. Moreover, muscle fibrosis can be treated specifically by in loco injection of Lv-mirAT1a without affecting other organs.

TGF-β-Induced Endothelial-Mesenchymal Transition in Fibrotic Diseases

Fibrotic diseases are characterized by net accumulation of extracellular matrix proteins in affected organs leading to their dysfunction and ultimate failure. Myofibroblasts have been identified as the cells responsible for the progression of the fibrotic process, and they originate from several sources, including quiescent tissue fibroblasts, circulating CD34⁺ fibrocytes and the phenotypic conversion of various cell types into activated myofibroblasts. Several studies have demonstrated that endothelial cells can transdifferentiate into mesenchymal cells through a process termed endothelial- mesenchymal transition (EndMT) and that this can give rise to activated myofibroblasts involved in the development of fibrotic diseases. Transforming growth factor β (TGF-β) has a central role in fibrogenesis by modulating the fibroblast phenotype and function, inducing myofibroblast transdifferentiation and promoting matrix accumulation. In addition, TGF-β by inducing EndMT may further contribute to the development of fibrosis. Despite extensive investigation of the pathogenesis of fibrotic diseases, no effective treatment strategies are available. Delineation of the mechanisms responsible for initiation and progression of fibrotic diseases is crucial for the development of therapeutic strategies for the treatment of the disease. In this review, we summarize the role of the TGF-β signaling pathway and EndMT in the development of fibrotic diseases and discuss their therapeutic potential.

Transforming Growth Factor-β: Master Regulator of the Respiratory System in Health and Disease

In this article, we review the biology and physiological importance of transforming growth factor-β (TGF-β) to homeostasis in the respiratory system, its importance to innate and adaptive immune responses in the lung, and its pathophysiological role in various chronic pulmonary diseases including pulmonary arterial hypertension, chronic obstructive pulmonary disease, asthma, and pulmonary fibrosis. The TGF-β family is responsible for initiation of the intracellular signaling pathways that direct numerous cellular activities including proliferation, differentiation, extracellular matrix synthesis, and apoptosis. When TGF-β signaling is dysregulated or essential control mechanisms are unbalanced, the consequences of organ and tissue dysfunction can be profound. The complexities and myriad checkpoints built into the TGF-β signaling pathways provide attractive targets for the treatment of these disease states, many of which are currently being investigated. This review focuses on those aspects of TGF-β biology that are most relevant to pulmonary diseases and that hold promise as novel therapeutic targets.

Osteopontin enhances multi-walled carbon nanotube-triggered lung fibrosis by promoting TGF-β1 activation and myofibroblast differentiation

BACKGROUND

Carbon nanotubes (CNTs) have been used in a variety of applications because of their unique properties and functions. However, many CNTs have been shown to induce lung fibrosis in experimental animals with some at a potency greater than that of silica, raising concern over possible toxic effects of CNT exposure in humans. Research into the mechanisms by which CNTs induce pulmonary fibrosis is warranted in order to facilitate the understanding, monitoring, and treatment of CNT-induced lung lesions that might occur in exposed populations. The current study focuses on investigating the role of osteopontin (OPN) in the development of lung fibrosis upon exposure to multi-walled carbon nanotubes (MWCNTs).

METHODS

C57BL/6J (WT) and Opn knockout (KO) mice were exposed to MWCNTs by pharyngeal aspiration to examine the acute and chronic effects of MWCNT exposure. The role of OPN and its mode of action in lung fibrosis development were analyzed at the cellular and molecular levels in vivo and in vitro.

RESULTS

OPN was highly and persistently induced in both the acute and chronic phases of the response to MWCNT exposure in mouse lungs. Comparison between WT and Opn KO mice revealed that OPN critically regulated MWCNT-induced lung fibrosis as indicated by reduced fibrotic focus formation and myofibroblast accumulation in Opn KO lungs. At the molecular level, OPN promotes the expression and activation of TGF-β1, stimulates the differentiation of myofibroblasts from fibroblasts, and increases the production of fibrous matrix proteins in lungs and cultured lung cells exposed to MWCNTs.

CONCLUSION

OPN is highly induced in CNT-exposed lungs and plays critical roles in TGF-β1 signaling activation and myofibroblast differentiation to promote fibrosis development from MWCNT exposure. This study reveals an OPN-dependent mechanism to promote MWCNT-induced lung fibrosis. The findings raise the possibility of using OPN as a biomarker to monitor CNT exposure and as a drug target to halt fibrosis development.