An Official American Thoracic Society Workshop Report: Use of Animal Models for the Preclinical Assessment of Potential Therapies for Pulmonary Fibrosis

ASK1 Regulates Bleomycin-induced Pulmonary Fibrosis

Pulmonary fibrosis (PF) is an abnormal remodeling of cellular composition and extracellular matrix that results in histological and functional alterations in the lungs. Apoptosis signal-regulating kinase-1 (ASK1) is a member of the mitogen-activated protein (MAP) kinase family that is activated by oxidative stress and promotes inflammation and apoptosis. Here we show that bleomycin-induced PF is reduced in Ask1 knockout mice (Ask1^-/-) compared with wild-type (WT) mice, with improved survival and histological and functional parameters restored to basal levels. In WT mice, bleomycin caused activation of ASK1, p38, and extracellular signal-regulated kinase 1/2 (ERK1/2) in lung tissue, as well as changes in redox indicators (thioredoxin and heme-oxygenase-1), collagen content, and epithelial-mesenchymal transition markers (EMTs). These changes were largely restored toward untreated WT control levels in bleomycin-treated Ask1^-/- mice. We further investigated whether treatment of WT mice with an ASK1 inhibitor, selonsertib (GS-4997), during the fibrotic phase would attenuate the development of PF. We found that pharmacological inhibition of ASK1 reduced activation of ASK1, p38, and ERK1/2 and promoted the restoration of redox and EMT indicators, as well as improvements in histological parameters. Our results suggest that ASK1 plays a central role in the development of bleomycin-induced PF in mice via p38 and ERK1/2 signaling. Together, these data indicate a possible therapeutic target for PF that involves an ASK1/p38/ERK1/2 axis.

The Latest in Animal Models of Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) describes heterogeneous population of patients with a mean pulmonary arterial pressure >20 mm Hg. Rarely, PH presents as a primary disorder but is more commonly part of a complex phenotype associated with comorbidities. Regardless of the cause, PH reduces life expectancy and impacts quality of life. The current clinical classification divides PH into 1 of 5 diagnostic groups to assign treatment. There are currently no pharmacological cures for any form of PH. Animal models are essential to help decipher the molecular mechanisms underlying the disease, to assign genotype-phenotype relationships to help identify new therapeutic targets, and for clinical translation to assess the mechanism of action and putative efficacy of new therapies. However, limitations inherent of all animal models of disease limit the ability of any single model to fully recapitulate complex human disease. Within the PH community, we are often critical of animal models due to the perceived low success upon clinical translation of new drugs. In this review, we describe the characteristics, advantages, and disadvantages of existing animal models developed to gain insight into the molecular and pathological mechanisms and test new therapeutics, focusing on adult forms of PH from groups 1 to 3. We also discuss areas of improvement for animal models with approaches combining several hits to better reflect the clinical situation and elevate their translational value.

Inhibition of lung microbiota-derived proapoptotic peptides ameliorates acute exacerbation of pulmonary fibrosis

Idiopathic pulmonary fibrosis is an incurable disease of unknown etiology. Acute exacerbation of idiopathic pulmonary fibrosis is associated with high mortality. Excessive apoptosis of lung epithelial cells occurs in pulmonary fibrosis acute exacerbation. We recently identified corisin, a proapoptotic peptide that triggers acute exacerbation of pulmonary fibrosis. Here, we provide insights into the mechanism underlying the processing and release of corisin. Furthermore, we demonstrate that an anticorisin monoclonal antibody ameliorates lung fibrosis by significantly inhibiting acute exacerbation in the human transforming growth factorβ1 model and acute lung injury in the bleomycin model. By investigating the impact of the anticorisin monoclonal antibody in a general model of acute lung injury, we further unravel the potential of corisin to impact such diseases. These results underscore the role of corisin in the pathogenesis of acute exacerbation of pulmonary fibrosis and acute lung injury and provide a novel approach to treating this incurable disease.

Selective Inhibition of Bromodomain-Containing Protein 4 Reduces Myofibroblast Transdifferentiation and Pulmonary Fibrosis

Idiopathic pulmonary fibrosis is a lethal disease driven by myofibroblast expansion. Currently no therapies exist that target the epigenetic mechanisms controlling myofibroblast transdifferentiation, which is responsible for unregulated extracellular matrix (ECM) production. We have recently shown that bromodomain-containing protein 4 (BRD4), an epigenetic regulator that forms a scaffold for nuclear activators and transcription factors, is essential for TGFβ-induced myofibroblast transdifferentiation. However, its role in the development and progression of pulmonary fibrosis in vivo has not been established. Here, we evaluate the hypothesis that BRD4 bromodomain interactions mediate myofibroblast expansion and fibrosing disease in vivo. C57BL/6J mice challenged with intratracheal bleomycin were systemically treated with a selective allosteric inhibitor of the BRD4 bromodomain 1 (BD1), ZL0591 (10 mg/kg), during the established fibrotic phase (14 days post-bleomycin) in a rigorous therapeutic paradigm. Eleven days after initiation of ZL0591 treatment (25 days post-bleomycin), we detected a significant improvement in blood O2 saturation compared to bleomycin/vehicle control. Twenty-eight days post-bleomycin, we observed a reduction in the volumetric Hounsfield Unit (HU) density by micro computed tomography (µCT) in the ZL0591-treated group, as well as a reduction in collagen deposition (hydroxyproline content) and severity of injury (Ashcroft scoring). Myofibroblast transdifferentiation was measured by smooth muscle α-actin (αSMA) staining, indicating a loss of this cell population in the ZL0591-treated group, and corresponded to reduced transcript levels of myofibroblast-associated extracellular matrix genes, tenascin-C and collagen 1α1. We conclude that BRD4 BD1 interactions are critical for myofibroblast transdifferentiation and fibrotic progression in a mouse model of pulmonary fibrosis.

IL10 trains macrophage profibrotic function after lung injury

Cx3cr1+ monocyte-derived macrophages (moMacs) are recruited to tissues after injury and are known to have profibrotic effects, but the cell-cell interactions and specific pathways that regulate this polarization and function are incompletely understood. Here we investigate the role of moMac-derived Pdgfa in bleomycin-induced lung fibrosis in mice. Deletion of Pdgfa with Cx3cr1-CreERT2 decreased bleomycin-induced lung fibrosis. Among a panel of in vitro macrophage polarizing stimuli, robust induction of Pdgfa was noted with IL10 in both mouse and human moMacs. Likewise, analysis of single-cell data revealed high expression of the receptor IL10RA in moMacs from human fibrotic lungs. Studies with IL10-GFP mice revealed that IL10-expressing cells were increased after injury in mice and colocalized with moMacs. Notably, deletion of IL10ra with Csf1r-Cre: IL10ra fl/fl mice decreased both Pdgfa expression in moMacs and lung fibrosis. Taken together, these findings reveal a novel, IL10-dependent mechanism of macrophage polarization leading to fibroblast activation after injury.

Physiologically variable ventilation prevents lung function deterioration in a model of pulmonary fibrosis

Positive pressure ventilation exerts an increased stress and strain in the presence of pulmonary fibrosis. Thus, ventilation strategies that avoid high pressures while maintaining lung aeration are of paramount importance. While physiologically variable ventilation (PVV) has proven beneficial in various models of pulmonary disease, its potential advantages in pulmonary fibrosis have not been investigated. Therefore, we assessed the benefit of PVV over conventional pressure-controlled ventilation (PCV) in a model of pulmonary fibrosis. Lung fibrosis was induced with intratracheal bleomycin in rabbits. Fifty days later, the animals were randomized to receive 6 hours of either PCV (n=10) or PVV (n=11). The PVV pattern was prerecorded in spontaneously breathing, healthy rabbits. Respiratory mechanics and gas exchange were assessed hourly, end-expiratory lung volume and intrapulmonary shunt fraction were measured at hours 0 and 6. Histological and cellular analyses were performed. Fifty days after bleomycin treatment, the rabbits presented elevated specific airway resistance (69±26% [mean±95%confidence interval]), specific tissue damping (38±15%) and specific elastance (47±16%) along with histological evidence of fibrosis. Six hours of PCV led to increased respiratory airway resistance (Raw, 111±30%), tissue damping (G, 36±13%) and elastance (H, 58±14%), and decreased end-expiratory lung volume (EELV, -26±7%) and oxygenation (PaO₂/FiO₂, -14±5%). The time-matched changes in the PVV group were significantly lower for G (22±9%), H (41±6%), EELV (-13±6%) and PaO₂/FiO₂ ratio (-3±5%, p<0.05 for all). There was no difference in histopathology between the ventilation modes. Thus, prolonged application of PVV prevented the deterioration of gas exchange by reducing atelectasis development in bleomycin-induced lung fibrosis.

Biomechanical Force and Cellular Stiffness in Lung Fibrosis

Lung fibrosis is characterized by the continuous accumulation of extracellular matrix (ECM) proteins produced by apoptosis-resistant (myo)fibroblasts. Lung epithelial injury promotes the recruitment and activation of fibroblasts, which are necessary for tissue repair and restoration of homeostasis. However, under pathologic conditions, a vicious cycle generated by profibrotic growth factors/cytokines, multicellular interactions, and matrix-associated signaling propagates the wound repair response and promotes lung fibrosis characterized not only by increased quantities of ECM proteins but also by changes in the biomechanical properties of the matrix. Importantly, changes in the biochemical and biomechanical properties of the matrix itself can serve to perpetuate fibroblast activity and propagate fibrosis, even in the absence of the initial stimulus of injury. The development of novel experimental models and methods increasingly facilitates our ability to interrogate fibrotic processes at the cellular and molecular levels. The goal of this review is to discuss the impact of ECM conditions in the development of lung fibrosis and to introduce new approaches to more accurately model the in vivo fibrotic microenvironment. This article highlights the pathologic roles of ECM in terms of mechanical force and the cellular interactions while reviewing in vitro and ex vivo models of lung fibrosis. The improved understanding of the fundamental mechanisms that contribute to lung fibrosis holds promise for identification of new therapeutic targets and improved outcomes.

Bimodal fibrosis in a novel mouse model of bleomycin-induced usual interstitial pneumonia

Idiopathic pulmonary fibrosis is pathologically represented by usual interstitial pneumonia (UIP). Conventional bleomycin models used to study pathogenic mechanisms of pulmonary fibrosis display transient inflammation and fibrosis, so their relevance to UIP is limited. We developed a novel chronic induced-UIP (iUIP) model, inducing fibrosis in D1CC×D1BC transgenic mice by intra-tracheal instillation of bleomycin mixed with microbubbles followed by sonoporation (BMS). A bimodal fibrotic lung disease was observed over 14 wk, with an acute phase similar to nonspecific interstitial pneumonia (NSIP), followed by partial remission and a chronic fibrotic phase with honeycombing similar to UIP. In this secondary phase, we observed poor vascularization despite elevated PDGFRβ expression. γ2PF- and MMP7-positive epithelial cells, consistent with an invasive phenotype, were predominantly adjacent to fibrotic areas. Most invasive cells were Scgb1a1 and/or Krt5 positive. This iUIP mouse model displays key features of idiopathic pulmonary fibrosis and has identified potential mechanisms contributing to the onset of NSIP and progression to UIP. The model will provide a useful tool for the assessment of therapeutic interventions to oppose acute and chronic fibrosis.

Lenalidomide attenuates post-inflammation pulmonary fibrosis through blocking NF-κB signaling pathway

Idiopathic pulmonary fibrosis (IPF) is a pathological consequence of interstitial pulmonary diseases, and is characterized by the persistence of fibroblasts and excessive deposition of extracellular matrix (ECM). The etiology of IPF is multifactorial. Although the role of inflammation in fibrogenesis is controversial, it is still recognized as an important component and epiphenomenon of IPF. Stimulus increase production of pro-inflammatory cytokines and activation of NF-κB, which will further promote inflammation response and myofibroblast transition. Lenalidomide is an immunomodulatory drug. Previous studies have revealed its anti-tumor effects through regulating immune response. Here we investigate the effect of lenalidomide on post-inflammation fibrosis. In vitro study revealed that lenalidomide inhibited NF-κB signaling in LPS-induced macrophage, and further attenuated macrophage-induced myofibroblast activation. Meanwhile, lenalidomide could inhibit TGF-β1-induced myofibroblast activation through suppressing TGF-β1 downstream MAPK signaling. In vivo study showed that lenalidomide inhibited pro-inflammatory cytokines TNF-α and IL-6 while enhanced anti-fibrotic cytokines IFN-γ and IL-10 in bleomycin-induced inflammation model, and attenuated pulmonary fibrosis and collagen deposition in the following fibrosis stage. In conclusion, our results demonstrate that lenalidomide possesses potential anti-fibrotic effects through suppressing NF-κB signaling.

Comparison of 3D airway models for the assessment of fibrogenic chemicals

Lung epithelial cells and fibroblasts play key roles in pulmonary fibrosis and are involved in fibrotic signaling and production of the extracellular matrix (ECM), respectively. Recently, 3D airway models consisting of both cell types have been developed to evaluate the fibrotic responses while facilitating cell-cell crosstalk. This study aimed to evaluate the fibrotic responses in these models using different fibrogenic agents, which are known as key events in adverse outcome pathways of pulmonary fibrosis. We quantified cell injury and several sequential steps in fibrogenesis, including inflammation, the epithelial-mesenchymal transition (EMT), fibroblast activation, and ECM accumulation, using two different 3D airway models, the EpiAirway™-full thickness (Epi/FT) and MucilAir™-human fibroblast (Mucil/HF) models. In the Epi/FT model, fibrogenic agents induced the expression of inflammation and EMT-associated markers, while in the Mucil/HF model, they induced fibroblast activation and ECM accumulation. Using this information, we conducted gene ontology term network analysis. In the Epi/FT model, the terms associated with cell migration and response to stimulus made up a large part of the network. In the Mucil/HF model, the terms associated with ECM organization and cell differentiation and proliferation constituted a great part of the network. Collectively, our data suggest that polyhexamethyleneguanidine phosphate and bleomycin induce different responses in the two 3D airway models. While Epi/FT was associated with inflammatory/EMT-associated responses, Mucil/HF was associated with fibroblast-associated responses. This study will provide an important basis for selecting proper 3D airway models and fibrogenic agents to further research or screen chemicals causing inhalation toxicity.

Tetrathiomolybdate Treatment Attenuates Bleomycin-Induced Angiogenesis and Lung Pathology in a Sheep Model of Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive chronic lung disease characterized by excessive extracellular matrix (ECM) deposition in the parenchyma of the lung. Accompanying the fibrotic remodeling, dysregulated angiogenesis has been observed and implicated in the development and progression of pulmonary fibrosis. Copper is known to be required for key processes involved in fibrosis and angiogenesis. We therefore hypothesized that lowering bioavailable serum copper with tetrathiomolybdate could be of therapeutic value for treating pulmonary fibrosis. This study aimed to investigate the effect of tetrathiomolybdate on angiogenesis and fibrosis induced in sheep lung segments infused with bleomycin. Twenty sheep received two fortnightly infusions of either bleomycin (3U), or saline (control) into two spatially separate lung segments. A week after the final bleomycin/saline infusions, sheep were randomly assigned into two groups (n = 10 per group) and received twice-weekly intravenous administrations of either 50 mg tetrathiomolybdate, or sterile saline (vehicle control), for 6 weeks. Vascular density, expressed as the percentage of capillary area to the total area of parenchyma, was determined in lung tissue sections immuno-stained with antibodies against CD34 and collagen type IV. The degree of fibrosis was assessed by histopathology scoring of H&E stained sections and collagen content using Masson's trichrome staining. Lung compliance was measured via a wedged bronchoscope procedure prior to and 7 weeks following final bleomycin infusion. In this large animal model, we show that copper lowering by tetrathiomolybdate chelation attenuates both bleomycin-induced angiogenesis and pulmonary fibrosis. Moreover, tetrathiomolybdate treatment downregulates vascular endothelial growth factor (VEGF) expression, and improved lung function in bleomycin-induced pulmonary fibrosis. Tetrathiomolybdate also suppressed the accumulation of inflammatory cells in bronchoalveolar lavage fluid 2 weeks after bleomycin injury. The molecular mechanism(s) underpinning copper modulation of fibrotic pathways is an important area for future investigation, and it represents a potential therapeutic target for pulmonary fibrosis.

Animal models of drug-induced pulmonary fibrosis: an overview of molecular mechanisms and characteristics

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease characterized by progressive loss of pulmonary function. Drug-induced interstitial lung disease has been reported as a severe adverse effect of some drugs, such as bleomycin, amiodarone, and methotrexate. Based on good characteristics, drug-induced pulmonary fibrosis (PF) animal model has played a key role in our understanding of the molecular mechanisms of PF pathogenesis and recapitulates the specific pathology in patients and helps develop therapeutic strategies. Here, we summarize the mechanisms and characteristics of given fibrotic drug-induced animal models for PFs. Together with the key publications describing these models, this brief but detailed overview would be helpful for the pharmacological research with animal models of PFs. Potential mechanisms underlying drug induced lung toxicity.

Cabozantinib ameliorates lipopolysaccharide-induced lung inflammation and bleomycin--induced early pulmonary fibrosis in mice

The lung, as the primary organ for gas exchange in mammals, is the main target organ for many pathogens and allergens, which may cause acute lung injury. A certain proportion of acute lung injury may progress into irreversible pulmonary fibrosis. Both acute lung injury and pulmonary fibrosis have high mortality rates and few effective treatments. Cabozantinib is a multi-target small molecule tyrosine kinase inhibitor and has been approved for the treatment of multiple malignant solid tumors. In this study, we explored the role of cabozantinib in acute lung injury and pulmonary fibrosis in vivo and in vitro. In the lipopolysaccharide and bleomycin induced mouse lung injury models, cabozantinib significantly improved the pathological state and reduced the infiltration of inflammatory cells in the lung tissues. In the bleomycin induced pulmonary fibrosis model, cabozantinib significantly reduced the area of pulmonary fibrosis and improved lung function in mice. The results of in vitro studies showed that cabozantinib could inhibit the inflammatory response and apoptosis of alveolar epithelial cells by inhibiting the activation of TLR4/NF-κB and NLRP3 inflammasome pathways. At the same time, cabozantinib could inhibit the activation of lung fibroblasts through suppressing the TGF-β1/Smad pathway, and promote the apoptosis of fibroblasts. In summary, cabozantinib could alleviate lung injury through regulating the TLR4 /NF-κB/NLRP3 inflammasome pathway, and alleviate pulmonary fibrosis by inhibiting the TGF-β1/Smad3 signaling pathway.

Intermittent hypoxia increases ROS/HIF-1α 'related oxidative stress and inflammation and worsens bleomycin-induced pulmonary fibrosis in adult male C57BL/6J mice

Obstructive sleep apnea (OSA) has been increasingly recognized as a risk factor for idiopathic pulmonary fibrosis (IPF). The intermittent hypoxia (IH) and re-oxygenation of OSA contribute to poor outcomes of IPF, however, the potential mechanism remains unknown. Here, C57BL/6J mice were administered intratracheal injection of Bleomycin (BLM) or saline and then exposed to IH (alternating cycles of FiO2 21% for 60S and FiO2 10% for 30 s, 40 cycles/hour, 8 h/day) to mimic OSA or intermittent air (IA) for 4 days, 8 days or 21 days. This study found that pulmonary fibrosis in BLM + IH treated mice was more severe than that in BLM + IA group at day 8 and 21, but not observed at day 4. Besides, the expression of reactive oxygen species (ROS) and hypoxia inducible factor-1α (HIF-1α),which are related to hypoxia reduced oxidative stress and inflammation, were higher in BLM + IH treated mice than BLM + IA mice, and IH increased these indexes in BLM treated mice from day 4 to day 21. Interestingly, a positive linear correlation between the HIF-1α expression and hydroxyproline (HYP) content was observed. We further found some inflammatory cells in bronchoalveolar lavage fluid were increased significantly from day 4 to 21, and there was a positive correlation between inflammation and ROS expression. Our results demonstrated that IH aggravated BLM-induced pulmonary fibrosis, and ROS/HIF-1α related oxidative stress and inflammation involved. The increase of ROS/HIF-1α related oxidative stress and inflammation may be a potential mechanism of moderate-to-severe OSA in potentiating pulmonary fibrosis of IPF, which warrants further study.

Feasibility of quantification of murine radiation-induced pulmonary fibrosis with microCT imaging

Mouse models of radiation-induced pulmonary fibrosis (RIPF) are commonly produced to find novel treatments for the condition. However, current models are not always assesed in a clinically-relevant manner. Clinics diagnose and track RIPF through CT scanning rather than observing time-to-death. An established timeline of RIPF lesion development in a murine model is therefore needed. Male C57Bl/6 mice (n=43) were irradiated with a single dose of 20 Gy to the whole thoracic area delivered by an 320 kV X-Rad cabinet irradiator. CT was performed with respitory gating at two week time points and developed images to identify RIPF pathology in vivo. Confirmation of CT findings was performed via histology on the lungs using Mason's trichrome staining. CT images were segmented to quantify fibrosis and lung which are then summed to give total volume. The fibrotic fraction was calculated upto 26 weeks. Significant increases in fibrotic fraction compared to the baseline microCT scans for each individual mouse acquired prior to the 20 Gy exposure are seen beginning at 10-12 weeks. Tidal lung volume was also calculated by subtracting expiration scan volumes from inspiration scan volumes. However the decrease in tidal lung volume over time was not statisitically significant. Computed tomography (CT) imaging was used to quantify the increase in fibrosis over time in our mouse model. However, the results were highly variable among individual mice after irradiation. CT imaging should be used in future studies looking at treatments for RIPF as it allows for measuring the extent of pathology non-invasively in a clinically-relevant manner.

Multipotent stromal cells: One name, multiple identities

Multipotent stromal cells (MSCs) are vital for development, maintenance, function, and regeneration of most tissues. They can differentiate along multiple connective lineages, but unlike most other stem/progenitor cells, they carry out various other functions while maintaining their developmental potential. MSCs function as damage sensors, respond to injury by fostering regeneration through secretion of trophic factors as well as extracellular matrix (ECM) molecules, and contribute to fibrotic reparative processes when regeneration fails. Tissue-specific MSC identity, fate(s), and function(s) are being resolved through fate mapping coupled with single cell "omics," providing unparalleled insights into the secret lives of tissue-resident MSCs.

Systems biology analysis of lung fibrosis-related genes in the bleomycin mouse model

Tissue fibrosis is a major driver of pathology in aging and is involved in numerous age-related diseases. The lungs are particularly susceptible to fibrotic pathology which is currently difficult to treat. The mouse bleomycin-induced fibrosis model was developed to investigate lung fibrosis and widely used over the years. However, a systematic analysis of the accumulated results has not been performed. We undertook a comprehensive data mining and subsequent manual curation, resulting in a collection of 213 genes (available at the TiRe database, www.tiredb.org ), which when manipulated had a clear impact on bleomycin-induced lung fibrosis. Our meta-analysis highlights the age component in pulmonary fibrosis and strong links of related genes with longevity. The results support the validity of the bleomycin model to human pathology and suggest the importance of a multi-target therapeutic strategy for pulmonary fibrosis treatment.

Intracellular hydroxyproline imprinting following resolution of bleomycin-induced pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease with few treatment options. The poor success in developing anti-IPF strategies have impelled researchers to reconsider the importance of choice for animal model and assessment methodologies. Currently, it is still not settled whether the bleomycin-induced lung fibrosis mouse model finally returns to resolution.This study aimed to follow the dynamic fibrotic features of BLM (Bleomycin)-treated mouse lungs with extended durations through a combination of the latest technologies (micro-CT imaging and histological detection of degraded collagens) with traditional methods. In addition, we also applied immunohistochemistry to explore the distribution of all hydroxyproline-containing molecules.As determined by classical biochemical method, total lung hydroxyproline contents reached peak at 4-week after bleomycin injury and maintained a steady high level thereafter until the end of the experiments (16-week). This result seemed to partially contradict with the changes of other fibrosis evaluation parameters, which indicated a gradual degradation of collagens and a recovery of lung aeration post the fibrosis peak. This inconsistency was well reconciled by our data from immunostaining against hydroxyproline and a fluorescent peptide staining against degraded collagen, together showing large amounts of hydroxyproline-rich degraded collagen fragments detained and enriched within the intracellular regions at 10- or 16-week, rather than at 4-week post the BLM-treatment. Hence, our present data not only offer respiratory researchers a new perspective towards the resolution nature of mouse lung fibrosis, but also remind them to be cautious while using hydroxyproline content assay to evaluate the severity of fibrosis.

Leveraging ageing models of pulmonary fibrosis: the efficacy of nintedanib in ageing

Nintedanib is one of two US Food and Drug Administration (FDA)-approved treatments for idiopathic pulmonary fibrosis (IPF). The clinical efficacy of nintedanib for inhibiting the progression of lung fibrosis is well-established [1]. However, although nintedanib is overwhelmingly prescribed to elderly patients, the impact of ageing on its efficacy is difficult to discern from clinical data due to the magnitude of confounding variables that exist among human subjects (genetics, gender, comorbidities, disease stage at the onset of treatment, etc.). A recent post hoc meta-analysis of five IPF clinical trials suggested that the effect of nintedanib in reducing the rate of forced vital capacity decline is consistent across patients with age (patients >75 versus patients <75 years of age) [2]. However, it is important to note that the average age of IPF diagnosis is 66 years and the average patient ages in these cohorts were 78 (>75) versus 64 (<75) years. Further, one could argue that patients in both cohorts represent the elderly population. This study highlights the complexity of evaluating the impact of ageing on efficacy in a clinical setting. To date, all pre-clinical efficacy studies with nintedanib have been performed in young animals. We therefore sought to determine whether ageing impacts the efficacy of nintedanib for inhibiting the development of lung fibrosis. Bleomycin-induced lung injury in young (2 month) and aged (18 month) mice was followed by treatment with nintedanib or vehicle from day 10–21 (figure 1a), using a previously described protocol [3]. We previously demonstrated in this injury model that the severity of lung fibrosis is identical in young and aged mice, in terms of the net increase in total lung collagen following injury [4]. Although some prior studies have reported seemingly contradictory results, indicating increased severity of fibrosis in aged mice [5, 6], this discrepancy could be attributed to increased baseline levels of collagen in aged mice and the methodology/analyses used for fibrosis assessment, as the net increase in collagen appear to be similar in both young and aged mice [5, 6]. In line with our previous findings, both young and aged vehicle-treated mice demonstrated similar levels of fibrosis severity and a similar decline in lung function at 3 weeks post-injury (figure 1b–d, g–h). Also consistent with numerous prior reports [7, 8], we found that in young mice, nintedanib demonstrated efficacy for inhibiting the development of fibrosis (figure 1b–g) and led to improved lung function (figure 1h). Interestingly, nintedanib also significantly inhibited the development of lung fibrosis in aged mice, to a similar extent as young cohorts (figure 1b–g). Although nintedanib treatment resulted in lung functional improvement to a similar extent in both young (49%) and aged (57%) mice (figure 1h), results did not reach statistical significance in aged mice. Of note, there is less than 47% power to detect mean differences between the aged-vehicle and aged-nintedanib groups given the observed effect and sample sizes of aged mice; the trending p-value of 0.06 is displayed to provide a better understanding of the results. No significant differences in survival rate were observed between nintedanib- versus vehicle-treated groups for both young (68% versus 72%, respectively) and aged mice (83% versus 76%, respectively) during this treatment period (day 10–21). Overall, these data indicate that ageing does not impact the efficacy of nintedanib in terms of its ability to inhibit the development of de novo lung fibrosis.

Although nintedanib is overwhelmingly prescribed to elderly patients, this is the first study to demonstrate that ageing does not impact the efficacy of nintedanib. This study sheds light on the utility of aged animal models in pulmonary fibrosis.https://bit.ly/3zA9RC5

SSC-ILD mouse model induced by osmotic minipump delivered bleomycin: effect of Nintedanib

Systemic sclerosis (SSc) is an autoimmune disease characterized by an excessive production and accumulation of collagen in the skin and internal organs often associated with interstitial lung disease (ILD). Its pathogenetic mechanisms are unknown and the lack of animal models mimicking the features of the human disease is creating a gap between the selection of anti-fibrotic drug candidates and effective therapies. In this work, we intended to pharmacologically validate a SSc-ILD model based on 1 week infusion of bleomycin (BLM) by osmotic minipumps in C57/BL6 mice, since it will serve as a tool for secondary drug screening. Nintedanib (NINT) has been used as a reference compound to investigate antifibrotic activity either for lung or skin fibrosis. Longitudinal Micro-CT analysis highlighted a significant slowdown in lung fibrosis progression after NINT treatment, which was confirmed by histology. However, no significant effect was observed on lung hydroxyproline content, inflammatory infiltrate and skin lipoatrophy. The modest pharmacological effect reported here could reflect the clinical outcome, highlighting the reliability of this model to better profile potential clinical drug candidates. The integrative approach presented herein, which combines longitudinal assessments with endpoint analyses, could be harnessed in drug discovery to generate more reliable, reproducible and robust readouts.

Human bone marrow-derived mesenchymal stromal cells cultured in serum-free media demonstrate enhanced antifibrotic abilities via prolonged survival and robust regulatory T cell induction in murine bleomycin-induced pulmonary fibrosis

Background

Mesenchymal stromal cells (MSCs) are a potential therapeutic tool for pulmonary fibrosis. However, ex vivo MSC expansion using serum poses risks of harmful immune responses or unknown pathogen infections in the recipients. Therefore, MSCs cultured in serum-free media (SF-MSCs) are ideal for clinical settings; however, their efficacy in pulmonary fibrosis is unknown. Here, we investigated the effects of SF-MSCs on bleomycin-induced pulmonary inflammation and fibrosis compared to those of MSCs cultured in serum-containing media (S-MSCs).

Methods

SF-MSCs and S-MSCs were characterized in vitro using RNA sequence analysis. The in vivo kinetics and efficacy of SF-MSC therapy were investigated using a murine model of bleomycin-induced pulmonary fibrosis. For normally distributed data, Student’s t test and one-way repeated measures analysis of variance followed by post hoc Tukey’s test were used for comparison between two groups and multiple groups, respectively. For non-normally distributed data, Kruskal–Wallis and Mann–Whitney U tests were used for comparison between groups, using e Bonferroni’s correction for multiple comparisons. All tests were two-sided, and P < 0.05 was considered statistically significant.

Results

Serum-free media promoted human bone marrow-derived MSC expansion and improved lung engraftment of intravenously administered MSCs in recipient mice. SF-MSCs inhibited the reduction in serum transforming growth factor-β1 and the increase of interleukin-6 in both the serum and the bronchoalveolar lavage fluid during bleomycin-induced pulmonary fibrosis. SF-MSC administration increased the numbers of regulatory T cells (Tregs) in the blood and lungs more strongly than in S-MSC administration. Furthermore, SF-MSCs demonstrated enhanced antifibrotic effects on bleomycin-induced pulmonary fibrosis, which were diminished by antibody-mediated Treg depletion.

Conclusions

SF-MSCs significantly suppressed BLM-induced pulmonary inflammation and fibrosis through enhanced induction of Tregs into the lungs and corrected the dysregulated cytokine balance. Therefore, SF-MSCs could be a useful tool for preventing pulmonary fibrosis progression without the demerits of serum use.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02574-5.

Protective Effect of Remdesivir Against Pulmonary Fibrosis in Mice

Pulmonary fibrosis is a known sequela of severe or persistent lung damage. Existing clinical, imaging and autopsy studies have shown that the lungs exhibit a pathological pulmonary fibrosis phenotype after infection with coronaviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Pulmonary fibrosis may be one of the most serious sequelae associated with coronavirus disease 2019 (COVID-19). In this study, we aimed to examine the preventative effects of the antiviral drug remdesivir on pulmonary fibrosis. We used a mouse model of bleomycin-induced pulmonary fibrosis to evaluate the effects of remdesivir on pulmonary fibrosis in vivo and further explored the potential pharmacological mechanisms of remdesivir in lung fibroblasts and alveolar epithelial cells in vitro. The preventive remdesivir treatment was started on the day of bleomycin installation, and the results showed that remdesivir significantly alleviated bleomycin-induced collagen deposition and improved pulmonary function. In vitro experiments showed that remdesivir dose-dependently suppressed TGF-β1-induced lung fibroblast activation and improved TGF-β1-induced alveolar epithelial to mesenchymal transition. Our results indicate that remdesivir can preventatively alleviate the severity of pulmonary fibrosis and provide some reference for the prevention of pulmonary fibrosis in patients with COVID-19.

The phosphodiesterase 4 inhibitor AA6216 suppresses activity of fibrosis-specific macrophages

Background

Idiopathic pulmonary fibrosis (IPF) is a form of chronic, progressive fibrosing interstitial pneumonia of unknown cause, with a poor prognosis. We previously showed the antifibrotic effects of a novel phosphodiesterase 4 (PDE4) inhibitor, AA6216. In this study, we examined the effect of AA6216 on the pulmonary accumulation of segregated-nucleus-containing atypical monocytes (SatMs), which produce tumor necrosis factor (TNF)-α and are involved in murine lung fibrosis.

Methods

Mice were treated with bleomycin intratracheally at day 0 and either 10 mg/kg AA6216, 100 mg/kg nintedanib, or vehicle orally once daily from day 0 to 8. On day 9, we isolated the bronchoalveolar lavage fluid and analyzed the SatM ratio. In addition, we evaluated the effect of AA6216 on TNF-α production from SatMs isolated from murine bone marrow.

Results

AA6216, and not the antifibrotic agent nintedanib, significantly suppressed the pulmonary accumulation of SatMs (AA6216: 68.3 ± 5.4%, Nintedanib: 129.8 ± 19.7%). Furthermore, AA6216 dose-dependently inhibited the production of TNF-α by SatMs.

Conclusions

AA6216 suppresses pathogenic SatMs in the lung, which contributes to its antifibrotic effects.

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Fibrosis-specific macrophages are critical for the development of lung fibrosis.

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The PDE4 inhibitor, AA6216, suppresses the pro-fibrotic activity of macrophages.

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AA6216 inhibits the pulmonary accumulation of fibrosis-specific macrophages.

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AA6216 inhibits the production of TNF-α by fibrosis-specific macrophages.

Current therapeutic strategies for respiratory diseases using mesenchymal stem cells

Mesenchymal stromal/stem cells (MSCs) have a great potential to proliferate, undergo multi-directional differentiation, and exert immunoregulatory effects. There is already much enthusiasm for their therapeutic potentials for respiratory inflammatory diseases. Although the mechanism of MSCs-based therapy has been well explored, only a few articles have summarized the key advances in this field. We hereby provide a review over the latest progresses made on the MSCs-based therapies for four types of inflammatory respiratory diseases, including idiopathic pulmonary fibrosis, acute respiratory distress syndrome, chronic obstructive pulmonary disease, and asthma, and the uncovery of their underlying mechanisms from the perspective of biological characteristics and functions. Furthermore, we have also discussed the advantages and disadvantages of the MSCs-based therapies and prospects for their optimization.

Evaluation on epithelial-mesenchymal state and microRNAs focusing on isolated alveolar epithelial cells from bleomycin injured rat lung

Several studies using bleomycin (BLM)-induced lung injury rat model revealed that epithelial-mesenchymal transition (EMT) contributes to pulmonary fibrosis. Conversely, microRNAs (miRNAs) are considered as useful markers of various diseases. In the present study, we aimed to characterize the EMT state through focusing on alveolar epithelial cells and identify the miRNAs that can be used as markers to predict pulmonary fibrosis using a BLM-induced lung injury rat model. Intratracheal administration of BLM increased hydroxyproline, a component of collagen, in lung tissues at day 14, but not at day 7. However, BLM induced EMT at day 7, which was accompanied with increased mRNA expression of α-smooth muscle actin, a representative EMT marker, in alveolar epithelium, thereby suggesting that EMT occurs prior to pulmonary fibrosis in alveolar epithelial cells. Using this rat model, the expression levels of several EMT-associated miRNAs were examined, and miR-222 was found to be upregulated in alveolar epithelial cells as well as bronchoalveolar lavage fluid from day 3. Our findings indicate that EMT in alveolar epithelial cells may occur before pulmonary fibrosis, and miR-222 may be used as a potential marker for early prediction of pulmonary fibrosis.

Invariant Natural Killer T cells coordinate removal of senescent cells

Background

The failure of immune surveillance to remove senescent cells drive age-related diseases. Here, we target an endogenous immune surveillance mechanism that can promote elimination of senescent cells and reverse disease progression.

Methods

We identify a class of lipid-activated T cells, invariant natural killer T cells (iNKTs) are involved in the removal of pathologic senescent cells. We use two disease models in which senescent cells accumulate to test whether activation of iNKT cells was sufficient to eliminate senescent cells in vivo.

Findings

Senescent preadipocytes accumulate in white adipose tissue of chronic high-fat diet (HFD) fed mice, and activation of iNKT cells with the prototypical glycolipid antigen alpha-galactosylceramide (αGalCer) led to a reduction of these cells with improved glucose control. Similarly, senescent cells accumulate within the lungs of mice injured by inhalational bleomycin, and αGalCer-induced activation of iNKT cells greatly limited this accumulation, decreased the lung fibrosis and improved survival. Furthermore, co-culture experiments showed that the preferential cytotoxic activity of iNKT cells to senescent cells is conserved in human cells.

Conclusions

These results uncover a senolytic capacity of tissue-resident iNKT cells and pave the way for anti-senescence therapies that target these cells and their mechanism of activation.

Bergenin attenuates bleomycin-induced pulmonary fibrosis in mice via inhibiting TGF-β1 signaling pathway

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease characterized by epithelial cell damage, fibroblast activation, and collagen deposition. IPF has high mortality and limited therapies, which urgently needs to develop safe and effective therapeutic drugs. Bergenin, a compound derived from a variety of medicinal plants, has demonstrated multiple pharmacological activities including anti-inflammatory and anti-tumor, also acts as a traditional Chinese medicine to treat chronic bronchitis, but its effect on the pulmonary fibrosis is unknown. In this study, we demonstrated that bergenin could attenuate bleomycin (BLM)-induced pulmonary fibrosis in mice. In vitro studies indicated that bergenin inhibited the transforming growth factor-β1 (TGF-β1)-induced fibroblast activation and the extracellular matrix accumulation by inhibiting the TGF-β1/Smad signaling pathway. Further studies showed that bergenin could induce the autophagy formation of myofibroblasts by suppressing the mammalian target of rapamycin signaling and that bergenin could promote the myofibroblast apoptosis. In vivo experiments revealed that bergenin substantially inhibited the myofibroblast activation and the collagen deposition and promoted the autophagy formation. Overall, our results showed that bergenin attenuated the BLM-induced pulmonary fibrosis in mice by suppressing the myofibroblast activation and promoting the autophagy and the apoptosis of myofibroblasts.

Mouse Models of Lung Fibrosis

The drug discovery pipeline, from discovery of therapeutic targets through preclinical and clinical development phases, to an approved product by health authorities, is a time-consuming and costly process, where a lead candidates' success at reaching the final stage is rare. Although the time from discovery to final approval has been reduced over the last decade, there is still potential to further optimize and streamline the evaluation process of each candidate as it moves through the different development phases. In this book chapter, we describe our preclinical strategies and overall decision-making process designed to evaluate the tolerability and efficacy of therapeutic candidates suitable for patients diagnosed with fibrotic lung disease. We also describe the benefits of conducting preliminary discovery trials, to aid in the selection of suitable primary and secondary outcomes to be further evaluated and assessed in subsequent internal and external validation studies. We outline all relevant research methodologies and protocols routinely performed by our research group and hope that these strategies and protocols will be a useful guide for biomedical and translational researchers aiming to develop safe and beneficial therapies for patients with fibrotic lung disease.

Animal and Human Models of Tissue Repair and Fibrosis: An Introduction

Reductionist cell culture systems are not only convenient but essential to understand molecular mechanisms of myofibroblast activation and action in carefully controlled conditions. However, tissue myofibroblasts do not act in isolation and the complexity of tissue repair and fibrosis in humans cannot be captured even by the most elaborate culture models. Over the past five decades, numerous animal models have been developed to study different aspects of myofibroblast biology and interactions with other cells and extracellular matrix. The underlying principles can be broadly classified into: (1) organ injury by trauma such as prototypical full thickness skin wounds or burns; (2) mechanical challenges, such as pressure overload of the heart by ligature of the aorta or the pulmonary vein; (3) toxic injury, such as administration of bleomycin to lungs and carbon tetrachloride to the liver; (4) organ infection with viruses, bacteria, and parasites, such as nematode infections of liver; (5) cytokine and inflammatory models, including local delivery or viral overexpression of active transforming growth factor beta; (6) "lifestyle" and metabolic models such as high-fat diet; and (7) various genetic models. We will briefly summarize the most widely used mouse models used to study myofibroblasts in tissue repair and fibrosis as well as genetic tools for manipulating myofibroblast repair functions in vivo.

3-Carbamoyl-proxyl nitroxide radicals attenuate bleomycin-induced pulmonary fibrosis in mice

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease with a poor prognosis and limited treatment options. Oxidative and nitrosative stress is implicated as one of the main pathogenic pathways in IPF. The rationale for the use of antioxidants to treat lung fibrosis is appealing, however to date a consistent beneficial effect for such an approach has not been observed. We have recently demonstrated that nitroxides, particularly 3-carbamoyl-proxyl (3-CP), markedly reduce airway inflammation, airway hyper-responsiveness, and protein nitration of the lung tissue in a mouse model of ovalbumin-induced acute asthma, thus prompting its use for the treatment of IPF. The present study investigates the effect of 3-CP on the development of lung fibrosis using the murine intratracheal bleomycin model. 3-CP was administered either intranasally or orally during the entire experiment or starting 7 days after induction of the lung injury. 3-CP was found to be both a preventive and a therapeutic drug reducing the lung fibrosis (histological score), the increase in collagen content, protein nitration, TGF-β levels, the degree of weight loss as well as inhibiting the impairment of lung function. Nitroxides are catalytic antioxidants that preferentially detoxify radicals, and therefore the effect of 3-CP on the severity of the disease supports the involvement of reactive oxygen and nitrogen species in the disease pathology.

Assessment of Alamandine in Pulmonary Fibrosis and Respiratory Mechanics in Rodents

Introduction

Pulmonary fibrosis (PF) is characterized by an accelerated decline in pulmonary function and has limited treatment options. Alamandine (ALA) is a recently described protective peptide of the renin-angiotensin system (RAS) with essential tasks in several conditions. Our group previously demonstrated that ALA is reduced by 365% in the plasma of patients with idiopathic PF, and thus, it is plausible to believe that stimulation of this peptide could represent an important therapeutic target. In this sense, this study investigates the effects of ALA in an experimental model of PF.

Materials and Methods

Bleomycin (BLM) was administrated in Wistar rats, and these fibrotic animals were treated with ALA for 14 days. Body weight, histology, respiratory, and hemodynamic parameters were analyzed to study the effects of ALA.

Results

ALA treatment attenuated the development of fibrosis (P < 0.0001), reduced respiratory system elastance (P < 0.0001), and preserved weight gain (P < 0.0001) in fibrotic animals without affecting the autonomic control of blood pressure and heart rate.

Conclusion

The data from this study demonstrate the potential of ALA to alleviate pulmonary fibrosis and improve respiratory system mechanics in vivo. The promising results encourage more detailed investigations of the potential of ALA as a future and efficient antifibrotic.

Linking Fibrotic Remodeling and Ultrastructural Alterations of Alveolar Epithelial Cells after Deletion of Nedd4-2

Our previous study showed that in adult mice, conditional Nedd4-2-deficiency in club and alveolar epithelial type II (AE2) cells results in impaired mucociliary clearance, accumulation of Muc5b and progressive, terminal pulmonary fibrosis within 16 weeks. In the present study, we investigated ultrastructural alterations of the alveolar epithelium in relation to interstitial remodeling in alveolar septa as a function of disease progression. Two, eight and twelve weeks after induction of Nedd4-2 knockout, lungs were fixed and subjected to design-based stereological investigation at the light and electron microscopic level. Quantitative data did not show any abnormalities until 8 weeks compared to controls. At 12 weeks, however, volume of septal wall tissue increased while volume of acinar airspace and alveolar surface area significantly decreased. Volume and surface area of alveolar epithelial type I cells were reduced, which could not be compensated by a corresponding increase of AE2 cells. The volume of collagen fibrils in septal walls increased and was linked with an increase in blood–gas barrier thickness. A high correlation between parameters reflecting interstitial remodeling and abnormal AE2 cell ultrastructure could be established. Taken together, abnormal regeneration of the alveolar epithelium is correlated with interstitial septal wall remodeling.

RS4651 suppresses lung fibroblast activation via the TGF-β1/SMAD signalling pathway

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a progressive disease resulting in respiratory failure with no efficient treatment options. We investigated the protective effect of RS4651 on pulmonary fibrosis in mice and the mechanism.

METHODS

Intratracheal injection of bleomycin (BLM) was used to induce pulmonary fibrosis in mice. RS4561 was administered intraperitoneally at different doses. Histopathological changes were observed. The level of alpha-smooth muscle actin (α-SMA) were also tested. In vitro, the proliferation and migratory effects of RS4651 treatment on MRC-5 cells pre-treated with transforming growth factor (TGF-β1) were examined. RNA-sequencing was used to detect differentially expressed target genes. Then, the expression of α-SMA, pSMAD2 and SMAD7 were analysed during RS4651 treatment of MRC-5 cells with or without silencing by SMAD7 siRNA.

RESULTS

Histopathological staining results showed decreased collagen deposition in RS4651 administered mice. Additionally, a lower level of α-SMA was also observed compared to the BLM group. The results of in vitro studies confirmed that RS4651 can inhibit the proliferation and migration, as well as α-SMA and pSMAD2 expression in MRC-5 cells treated with TGF-β1. RNA-sequencing data identified the target gene SMAD7. We found that RS4651 could upregulate SMAD7 expression and inhibit the proliferation and migration of MRC-5 cells via SMAD7, and RS4651 inhibition of α-SMA and pSMAD2 expression was blocked in SMAD7-siRNA MRC-5 cells. In vivo studies further confirmed that RS4651 could upregulate SMAD7 expression in BLM-induced lung fibrosis in mice.

CONCLUSIONS

Our data suggest that RS4651 alleviates BLM-induced pulmonary fibrosis in mice by inhibiting the TGF-β1/SMAD signalling pathway.

Dissecting the Role of Mesenchymal Stem Cells in Idiopathic Pulmonary Fibrosis: Cause or Solution

Idiopathic pulmonary fibrosis (IPF) is one of the most aggressive forms of idiopathic interstitial pneumonias, characterized by chronic and progressive fibrosis subverting the lung's architecture, pulmonary functional decline, progressive respiratory failure, and high mortality (median survival 3 years after diagnosis). Among the mechanisms associated with disease onset and progression, it has been hypothesized that IPF lungs might be affected either by a regenerative deficit of the alveolar epithelium or by a dysregulation of repair mechanisms in response to alveolar and vascular damage. This latter might be related to the progressive dysfunction and exhaustion of the resident stem cells together with a process of cellular and tissue senescence. The role of endogenous mesenchymal stromal/stem cells (MSCs) resident in the lung in the homeostasis of these mechanisms is still a matter of debate. Although endogenous MSCs may play a critical role in lung repair, they are also involved in cellular senescence and tissue ageing processes with loss of lung regenerative potential. In addition, MSCs have immunomodulatory properties and can secrete anti-fibrotic factors. Thus, MSCs obtained from other sources administered systemically or directly into the lung have been investigated for lung epithelial repair and have been explored as a potential therapy for the treatment of lung diseases including IPF. Given these multiple potential roles of MSCs, this review aims both at elucidating the role of resident lung MSCs in IPF pathogenesis and the role of administered MSCs from other sources for potential IPF therapies.

Chronic lung inflammation and pulmonary fibrosis after multiple intranasal instillation of PM2 .5 in mice

Fine particulate matter (PM_2.5 ) is an important component of air pollution and can induce lung inflammation and oxidative stress. We hypothesized that PM_2.5 could play a role in the induction of pulmonary fibrosis. We examined whether multiple intranasal instillation of PM_2.5 can induce pulmonary fibrosis in the mouse, and also investigated the underlying pro-fibrotic signaling pathways. C57/BL6 mice were intranasally instilled with 50 μl of PM_2.5 suspension (7.8 μg/g body weight) or PBS three times a week over 3 weeks, 6 weeks or 9 weeks. To observe the recovery of pulmonary fibrosis after the termination of PM_2.5 exposure, 9 week-PM_2.5 instilled mice were also studied at 3 weeks after termination of instillation. There were significant decreases in total lung capacity (TLC) and compliance (Cchord) in the 9-week PM_2.5 -instilled mice, while there were increased histological fibrosis scores with enhanced type I collagen and hydroxyproline deposition, increased mitochondrial ROS levels and NOX activity, decreased total SOD and GSH levels, accompanied by decreased mitochondrial number and aberrant mitochondrial morphology (swelling, vacuolization, cristal disruption, reduced matrix density) in PM_2.5 -instilled mice. Multiple PM_2.5 instillation resulted in increased expression of TGFβ1, increases of N-Cadherin and Vimentin and a decrease of E-Cadherin. It also led to decreases in OPA1 and MFN2, and increases in Parkin, SQSTM1/p62, the ratio of light china (LC) 3B II to LC3B I, PI3k/Akt phosphorylation, and NLRP3 expression. Intranasal instillation of PM_2.5 for 9 weeks induced lung inflammation and pulmonary fibrosis, which was linked with aberrant epithelial-mesenchymal transition, oxidative stress, mitochondrial damage and mitophagy, as well as activation of TGFβ1-PI3K/Akt, TGFβ1- NOX and TGFβ1-NLRP3 pathways.

CB1 R and iNOS are distinct players promoting pulmonary fibrosis in Hermansky-Pudlak syndrome

Hermansky-Pudlak syndrome (HPS) is a rare genetic disorder which, in its most common and severe form, HPS-1, leads to fatal adult-onset pulmonary fibrosis (PF) with no effective treatment. We evaluated the role of the endocannabinoid/CB1 R system and inducible nitric oxide synthase (iNOS) for dual-target therapeutic strategy using human bronchoalveolar lavage fluid (BALF), lung samples from patients with HPS and controls, HPS-PF patient-derived lung fibroblasts, and bleomycin-induced PF in pale ear mice (HPS1ep/ep ). We found overexpression of CB1 R and iNOS in fibrotic lungs of HPSPF patients and bleomycin-infused pale ear mice. The endocannabinoid anandamide was elevated in BALF and negatively correlated with pulmonary function parameters in HPSPF patients and pale ear mice with bleomycin-induced PF. Simultaneous targeting of CB1 R and iNOS by MRI-1867 yielded greater antifibrotic efficacy than inhibiting either target alone by attenuating critical pathologic pathways. Moreover, MRI-1867 treatment abrogated bleomycin-induced increases in lung levels of the profibrotic interleukin-11 via iNOS inhibition and reversed mitochondrial dysfunction via CB1 R inhibition. Dual inhibition of CB1 R and iNOS is an effective antifibrotic strategy for HPSPF.

A novel multikinase inhibitor SKLB-YTH-60 ameliorates inflammation and fibrosis in bleomycin-induced lung fibrosis mouse models

OBJECTIVES

Idiopathic pulmonary fibrosis (IPF) is marked by the excessive accumulation of extracellular matrix, which participates in a variety of chronic diseases or injuries and seriously threatens human health. Due to the side effects of clinical drugs, there is still a need to develop novel and less toxic drugs to treat pulmonary fibrosis.

MATERIALS AND METHODS

SKLB-YTH-60 was developed through computer-aided drug design, de novo synthesis and high-throughput screening. We employed the bleomycin (BLM)-induced lung fibrosis animal models and used TGF-β₁ to induce the epithelial-mesenchymal transition (EMT) of A549 cells in vitro. Meanwhile, the protein expression of collagen I and the α-smooth muscle actin (α-SMA), E-cadherin, p-FGFR1, p-PLCγ, p-Smad2/3 and p-Erk1/2 was detected by western blot.

RESULTS

YTH-60 has obvious anti-proliferative activity on fibroblasts and A549 cells. Moreover, YTH-60 could impair the EMT of A549 cells and suppressed fibrosis by inhibiting FGFR and TGF-β/Smad-dependent pathways. Intraperitoneal administration of preventive YTH-60 could significantly reduce the degree of fibrosis in mice and regulate the imbalance of the immune microenvironment. In addition, we observed that therapeutic YTH-60 treatment attenuated fibrotic changes in mice during the period of fibrosis. Importantly, YTH-60 has shown an acceptable oral bioavailability (F = 17.86%) and appropriate eliminated half-life time (T_1/2  = 8.03 hours).

CONCLUSIONS

Taken together, these preclinical evaluations suggested that YTH-60 could be a promising drug candidate for treating IPF.

Molecular Pathogenesis of Pulmonary Fibrosis, with Focus on Pathways Related to TGF-β and the Ubiquitin-Proteasome Pathway

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal interstitial lung disease. During the past decade, novel pathogenic mechanisms of IPF have been elucidated that have shifted the concept of IPF from an inflammatory-driven to an epithelial-driven disease. Dysregulated repair responses induced by recurrent epithelial cell damage and excessive extracellular matrix accumulation result in pulmonary fibrosis. Although there is currently no curative therapy for IPF, two medications, pirfenidone and nintedanib, have been introduced based on understanding the pathogenesis of the disease. In this review, we discuss advances in understanding IPF pathogenesis, highlighting epithelial-mesenchymal transition (EMT), the ubiquitin-proteasome system, and endothelial cells. TGF-β is a central regulator involved in EMT and pulmonary fibrosis. HECT-, RING finger-, and U-box-type E3 ubiquitin ligases regulate TGF-β-Smad pathway-mediated EMT via the ubiquitin-proteasome pathway. p27 degradation mediated by the SCF-type E3 ligase, Skp2, contributes to the progression of pulmonary fibrosis by promotion of either mesenchymal fibroblast proliferation, EMT, or both. In addition to fibroblasts as key effector cells in myofibroblast differentiation and extracellular matrix deposition, endothelial cells also play a role in the processes of IPF. Endothelial cells can transform into myofibroblasts; therefore, endothelial-mesenchymal transition can be another source of myofibroblasts.

Hyperbaric Oxygen Ameliorates Bleomycin-Induced Pulmonary Fibrosis in Mice

The prevalence of pulmonary fibrosis is increasing with an aging population and its burden is likely to increase following COVID-19, with large financial and medical implications. As approved therapies in pulmonary fibrosis only slow disease progression, there is a significant unmet medical need. Hyperbaric oxygen (HBO) is the inhaling of pure oxygen, under the pressure of greater than one atmosphere absolute, and it has been reported to improve pulmonary function in patients with pulmonary fibrosis. Our recent study suggested that repetitive HBO exposure may affect biological processes in mice lungs such as response to wounding and extracellular matrix. To extend these findings, a bleomycin-induced pulmonary fibrosis mouse model was used to evaluate the effect of repetitive HBO exposure on pulmonary fibrosis. Building on our previous findings, we provide evidence that HBO exposure attenuates bleomycin-induced pulmonary fibrosis in mice. In vitro, HBO exposure could reverse, at least partially, transforming growth factor (TGF)-β-induced fibroblast activation, and this effect may be mediated by downregulating TGF-β-induced expression of hypoxia inducible factor (HIF)-1α. These findings support HBO as a potentially life-changing therapy for patients with pulmonary fibrosis, although further research is needed to fully evaluate this.

Increased expression of transient receptor potential channels and neurogenic factors associates with cough severity in a guinea pig model

BACKGROUND

Previous studies suggest that transient receptor potential (TRP) channels and neurogenic inflammation may be involved in idiopathic pulmonary fibrosis (IPF)-related high cough sensitivity, although the details of mechanism are largely unknown. Here, we aimed to further explore the potential mechanism involved in IPF-related high cough sensitivity to capsaicin challenge in a guinea pig model of pulmonary fibrosis induced by bleomycin.

METHODS

Western blotting and real-time quantitative polymerase chain reaction (RT-qPCR) were employed to measure the expression of TRP channel subfamily A, member 1 (TRPA1) and TRP vanilloid 1 (TRPV1), which may be involved in the cough reflex pathway. Immunohistochemical analysis and RT-qPCR were used to detect the expression of neuropeptides substance P (SP), Neurokinin-1 receptor (NK1R), and calcitonin gene-related peptide (CGRP) in lung tissues. Concentrations of nerve growth factor (NGF), SP, neurokinin A (NKA), neurokinin B (NKB), and brain-derived neurotrophic factor (BDNF) in lung tissue homogenates were measured by ELISA.

RESULTS

Cough sensitivity to capsaicin was significantly higher in the model group than that of the sham group. RT-qPCR and immunohistochemical analysis showed that the expression of TRPA1 and TRPV1 in the jugular ganglion and nodal ganglion, and SP, NK1R, and CGRP in lung tissue was significantly higher in the model group than the control group. In addition, expression of TRP and neurogenic factors was positively correlated with cough sensitivity of the experimental animals.

CONCLUSION

Up-regulated expression of TRPA1 and TRPV1 in the cough reflex pathway and neurogenic inflammation might contribute to the IPF-related high cough sensitivity in guinea pig model.

Persistent, Progressive Pulmonary Fibrosis and Epithelial Remodeling in Mice

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic interstitial lung disease with underlying mechanisms that have been primarily investigated in mice after intratracheal instillation of a single dose of bleomycin. However, the model has significant limitations, including transient fibrosis that spontaneously resolves and its failure to fully recapitulate the epithelial remodeling in the lungs of patients with IPF. Thus, there remains an unmet need for a preclinical model with features that more closely resemble the human disease. Repetitive intratracheal instillation of bleomycin has previously been shown to recapitulate some of these features, but the instillation procedure is complex, and the long-term consequences on epithelial remodeling and fibrosis persistence and progression remain poorly understood. Here, we developed a simplified repetitive bleomycin instillation strategy consisting of three bi-weekly instillations that leads to persistent and progressive pulmonary fibrosis. Lung histology demonstrates increased collagen deposition, fibroblast accumulation, loss of type I and type II alveolar epithelial cells within fibrotic areas, bronchiolization of the lung parenchyma with CCSP+ cells, remodeling of the distal lung into cysts reminiscent of simple honeycombing, and accumulation of hyperplastic transitional KRT8+ epithelial cells. Micro-computed tomographic imaging demonstrated significant traction bronchiectasis and subpleural fibrosis. Thus, the simplified repetitive bleomycin instillation strategy leads to progressive fibrosis and recapitulates the histological and radiographic characteristics of IPF. Compared with the single bleomycin instillation model, we suggest that the simplified repetitive instillation model may be better suited to address mechanistic questions about IPF pathogenesis and preclinical studies of antifibrotic drug candidates.

Serum-circulating His-tRNA synthetase inhibits organ-targeted immune responses

His-tRNA synthetase (HARS) is targeted by autoantibodies in chronic and acute inflammatory anti-Jo-1-positive antisynthetase syndrome. The extensive activation and migration of immune cells into lung and muscle are associated with interstitial lung disease, myositis, and morbidity. It is unknown whether the sequestration of HARS is an epiphenomenon or plays a causal role in the disease. Here, we show that HARS circulates in healthy individuals, but it is largely undetectable in the serum of anti-Jo-1-positive antisynthetase syndrome patients. In cultured primary human skeletal muscle myoblasts (HSkMC), HARS is released in increasing amounts during their differentiation into myotubes. We further show that HARS regulates immune cell engagement and inhibits CD4+ and CD8+ T-cell activation. In mouse and rodent models of acute inflammatory diseases, HARS administration downregulates immune activation. In contrast, neutralization of extracellular HARS by high-titer antibody responses during tissue injury increases susceptibility to immune attack, similar to what is seen in humans with anti-Jo-1-positive disease. Collectively, these data suggest that extracellular HARS is homeostatic in normal subjects, and its sequestration contributes to the morbidity of the anti-Jo-1-positive antisynthetase syndrome.

Sex-Related Differences in Murine Models of Chemically Induced Pulmonary Fibrosis

We developed two models of chemically induced chronic lung injury and pulmonary fibrosis in mice (intratracheally administered hydrochloric acid (HCl) and intratracheally administered nitrogen mustard (NM)) and investigated male–female differences. Female mice exhibited higher 30-day survival and less weight loss than male mice. Thirty days after the instillation of either HCl or NM, bronchoalveolar lavage fluid displayed a persistent, mild inflammatory response, but with higher white blood cell numbers and total protein content in males vs. females. Furthermore, females exhibited less collagen deposition, milder pulmonary fibrosis, and lower Ashcroft scores. After instillation of either HCl or NM, all animals displayed increased values of phosphorylated (activated) Heat Shock Protein 90, which plays a crucial role in the alveolar wound-healing processes; however, females presented lower activation of both transforming growth factor-β (TGF-β) signaling pathways: ERK and SMAD. We propose that female mice are protected from chronic complications of a single exposure to either HCl or NM through a lesser activation of TGF-β and downstream signaling. The understanding of the molecular mechanisms that confer a protective effect in females could help develop new, gender-specific therapeutics for IPF.

Lung organoids and other preclinical models of pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive fatal disease affecting over 100 000 people in Europe with an increasing incidence. Available treatments offer only slowing of disease progression and are poorly tolerated by patients leading to cessation of therapy. Lung transplant remains the only cure. Therefore, alternative treatments are urgently required. The pathology of IPF is complex and poorly understood and thus creates a major obstacle to the discovery of novel treatments. Additionally, preclinical assessment of new treatments currently relies upon animal models where disparities with human lung biology often hamper drug development. At a cellular level, IPF is characterized by persistent and abnormal deposition of extracellular matrix by fibroblasts and alveolar epithelial cell injury which is seen as a key event in initiation of disease progression. In-depth investigation of the role of alveolar epithelial cells in health and disease has been impeded due to difficulties in primary cell isolation and culture ex vivo. Novel strategies employing patient-derived induced pluripotent stem cells engineered to produce type 2 alveolar epithelial cells (iAEC2) cultured as three-dimensional organoids have the potential to overcome these hurdles and inform new effective precision treatments for IPF leading to improved survival and quality of life for patients worldwide.

Deglycosylated Azithromycin Attenuates Bleomycin-Induced Pulmonary Fibrosis via the TGF-β1 Signaling Pathway

Idiopathic pulmonary fibrosis (IPF) is a progressive, life-threatening lung disease characterized by the proliferation of myofibroblasts and deposition of extracellular matrix that results in irreversible distortion of the lung structure and the formation of focal fibrosis. The molecular mechanism of IPF is not fully understood, and there is no satisfactory treatment. However, most studies suggest that abnormal activation of transforming growth factor-β1 (TGF-β1) can promote fibroblast activation and epithelial to mesenchymal transition (EMT) to induce pulmonary fibrosis. Deglycosylated azithromycin (Deg-AZM) is a compound we previously obtained by removing glycosyls from azithromycin; it was demonstrated to exert little or no antibacterial effects. Here, we discovered a new function of Deg-AZM in pulmonary fibrosis. In vivo experiments showed that Deg-AZM could significantly reduce bleomycin-induced pulmonary fibrosis and restore respiratory function. Further study revealed the anti-inflammatory and antioxidant effects of Deg-AZM in vivo. In vitro experiments showed that Deg-AZM inhibited TGF-β1 signaling, weakened the activation and differentiation of lung fibroblasts, and inhibited TGF-β1-induced EMT in alveolar epithelial cells. In conclusion, our findings show that Deg-AZM exerts antifibrotic effects by inhibiting TGF-β1-induced myofibroblast activation and EMT.

Human-Based Advanced in vitro Approaches to Investigate Lung Fibrosis and Pulmonary Effects of COVID-19

The coronavirus disease 2019 (COVID-19) pandemic has caused considerable socio-economic burden, which fueled the development of treatment strategies and vaccines at an unprecedented speed. However, our knowledge on disease recovery is sparse and concerns about long-term pulmonary impairments are increasing. Causing a broad spectrum of symptoms, COVID-19 can manifest as acute respiratory distress syndrome (ARDS) in the most severely affected patients. Notably, pulmonary infection with Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2), the causing agent of COVID-19, induces diffuse alveolar damage (DAD) followed by fibrotic remodeling and persistent reduced oxygenation in some patients. It is currently not known whether tissue scaring fully resolves or progresses to interstitial pulmonary fibrosis. The most aggressive form of pulmonary fibrosis is idiopathic pulmonary fibrosis (IPF). IPF is a fatal disease that progressively destroys alveolar architecture by uncontrolled fibroblast proliferation and the deposition of collagen and extracellular matrix (ECM) proteins. It is assumed that micro-injuries to the alveolar epithelium may be induced by inhalation of micro-particles, pathophysiological mechanical stress or viral infections, which can result in abnormal wound healing response. However, the exact underlying causes and molecular mechanisms of lung fibrosis are poorly understood due to the limited availability of clinically relevant models. Recently, the emergence of SARS-CoV-2 with the urgent need to investigate its pathogenesis and address drug options, has led to the broad application of in vivo and in vitro models to study lung diseases. In particular, advanced in vitro models including precision-cut lung slices (PCLS), lung organoids, 3D in vitro tissues and lung-on-chip (LOC) models have been successfully employed for drug screens. In order to gain a deeper understanding of SARS-CoV-2 infection and ultimately alveolar tissue regeneration, it will be crucial to optimize the available models for SARS-CoV-2 infection in multicellular systems that recapitulate tissue regeneration and fibrotic remodeling. Current evidence for SARS-CoV-2 mediated pulmonary fibrosis and a selection of classical and novel lung models will be discussed in this review.

Gene therapy strategies for idiopathic pulmonary fibrosis: recent advances, current challenges, and future directions

Idiopathic pulmonary fibrosis (IPF) is a chronic disease in which the lungs become irreversibly scarred, leading to declining lung function. As currently available drugs do not cure IPF, there remains a great medical need for more effective treatments. Perhaps this need could be addressed by gene therapies, which offer powerful and versatile ways to attenuate a wide range of processes involved in fibrosis. Despite the potential benefits of gene therapy, no one has reviewed the current state of knowledge regarding its application for treating IPF. We therefore analyzed publications that reported the use of gene therapies to treat pulmonary fibrosis in animals, as clinical studies have not been published yet. In this review, we first provide an introduction on the pathophysiology of IPF and the most well-established gene therapy approaches. We then present a comprehensive evaluation of published animal studies, after which we provide recommendations for future research to address challenges with respect to the selection and use of animal models as well as the development of delivery vectors and dosage forms. Addressing these considerations will bring gene therapies one step closer to clinical testing and thus closer to patients.

Therapeutic Applications of Mesenchymal Stem Cells in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is an interstitial disease of unknown etiology characterized by progressive pulmonary fibrosis. Pirfenidone and nintedanib are the only drugs that can prolong the time to disease progression, slow down the decline in lung function, and prolong survival. However, they do not offer a cure and are associated with tolerability issues. The pluripotency of mesenchymal stem cells (MSCs) and their ability to regulate immunity, inhibit inflammation, and promote epithelial tissue repair highlight the promise of MSC therapy for treating interstitial lung disease. However, optimal protocols are lacking for multi-parameter selection in MSC therapy. This review summarizes preclinical studies on MSC transplantation for the treatment of interstitial lung disease and clinical studies with known results. An analysis of relevant factors for the optimization of treatment plans is presented, including MSCs with different sources, administration routes and timing, dosages, frequencies, and pretreatments with MSCs. This review proposes an optimized plan for guiding the design of future clinical research to identify therapeutic options for this complex disease.

Prenatal indole-3-carbinol administration activates aryl hydrocarbon receptor-responsive genes and attenuates lung injury in a bronchopulmonary dysplasia model

Hyperoxia-hypoxia exposure is a proposed cause of alveolar developmental arrest in bronchopulmonary dysplasia in preterm infants, where mitochondrial reactive oxygen species and oxidative stress vulnerability are increased. The aryl hydrocarbon receptor (AhR) is one of the main activators of the antioxidant enzyme system that protects tissues and systems from damage. The present study aimed to determine if the activation of the AhR signaling pathway by prenatal administration of indole-3-carbinol (I3C) protects rat pups from hyperoxia-hypoxia-induced lung injury. To assess the activation of protein-encoding genes related to the AhR signaling pathway (Cyp1a1, Cyp1b1, Ugt1a6, Nqo1, and Gsta1), pup lungs were excised at 0, 24, and 72 h after birth, and mRNA expression levels were quantified by reverse transcription-quantitative polymerase chain reaction assays (RT-qPCR). An adapted Ratner's method was used in rats to evaluate radial alveolar counts (RACs) and the degree of fibrosis. The results reveal that the relative expression of AhR-related genes in rat pups of prenatally I3C-treated dams was significantly different from that of untreated dams. The RAC was significantly lower in the hyperoxia-hypoxia group (4.0 ± 1.0) than that in the unexposed control group (8.0 ± 2.0; P < 0.01). When rat pups of prenatally I3C-treated dams were exposed to hyperoxia-hypoxia, an RAC recovery was observed, and the fibrosis index was similar to that of the unexposed control group. A cytokine antibody array revealed an increase in the NF-κB signaling cascade in I3C-treated pups, suggesting that the pathway could regulate the inflammatory process under the stimulus of this compound. In conclusion, the present study demonstrates that I3C prenatal treatment activates AhR-responsive genes in pup's lungs and hence attenuates lung damage caused by hyperoxia-hypoxia exposure in newborns.

Anti-fibrotic effects of different sources of MSC in bleomycin-induced lung fibrosis in C57BL6 male mice

BACKGROUND AND OBJECTIVE

IPF is a fatal and debilitating lung disorder increasing in incidence worldwide. To date, two approved treatments only slow disease progression, have multiple side effects and do not provide a cure. MSC have promising therapeutic potential as a cell-based therapy for many lung disorders based on the anti-fibrotic properties of the MSC.

METHODS

Critical questions remain surrounding the optimal source, timing and efficacy of cell-based therapies. The present study examines the most effective sources of MSC. Human MSC were derived from adipose, WJ, chorionic membrane (CSC) and chorionic villi (CVC). MSC were injected into the ageing mouse model of BLM-induced lung fibrosis.

RESULTS

All sources decreased Aschroft and hydroxyproline levels when injected into BLM-treated mice at day 10 with the exception of CSC cells that did not change hydroxyproline levels. There were also decreases in mRNA expression of αv -integrin and TNFα in all sources except CSC. Only ASC- and WJ-derived cells reduced AKT and MMP-2 activation, while Cav-1 was increased by ASC treatment as previously reported. BLM-induced miR dysregulation of miR-29 and miR-199 was restored only by ASC treatment.

CONCLUSION

Our data suggest that sources of MSC may differ in the pathway(s) involved in repair.