Fibrosis of two: Epithelial cell-fibroblast interactions in pulmonary fibrosis

Aberrant Activation of Wound-Healing Programs within the Metastatic Niche Facilitates Lung Colonization by Osteosarcoma Cells

PURPOSE

Lung metastasis is responsible for nearly all deaths caused by osteosarcoma, the most common pediatric bone tumor. How malignant bone cells coerce the lung microenvironment to support metastatic growth is unclear. The purpose of this study is to identify metastasis-specific therapeutic vulnerabilities by delineating the cellular and molecular mechanisms underlying osteosarcoma lung metastatic niche formation.

EXPERIMENTAL DESIGN

Using single-cell RNA sequencing, we characterized genome- and tissue-wide molecular changes induced within lung tissues by disseminated osteosarcoma cells in both immunocompetent murine models of metastasis and patient samples. We confirmed transcriptomic findings at the protein level and determined spatial relationships with multiparameter immunofluorescence and spatial transcriptomics. Based on these findings, we evaluated the ability of nintedanib, a kinase inhibitor used to treat patients with pulmonary fibrosis, to impair metastasis progression in both immunocompetent murine osteosarcoma and immunodeficient human xenograft models. Single-nucleus and spatial transcriptomics were used to perform molecular pharmacodynamic studies that define the effects of nintedanib on tumor and nontumor cells within the metastatic microenvironment.

RESULTS

Osteosarcoma cells induced acute alveolar epithelial injury upon lung dissemination. Single-cell RNA sequencing demonstrated that the surrounding lung stroma adopts a chronic, nonresolving wound-healing phenotype similar to that seen in other models of lung injury. Accordingly, the metastasis-associated lung demonstrated marked fibrosis, likely because of the accumulation of pathogenic, profibrotic, partially differentiated epithelial intermediates and macrophages. Our data demonstrated that nintedanib prevented metastatic progression in multiple murine and human xenograft models by inhibiting osteosarcoma-induced fibrosis.

CONCLUSIONS

Fibrosis represents a targetable vulnerability to block the progression of osteosarcoma lung metastasis. Our data support a model wherein interactions between osteosarcoma cells and epithelial cells create a prometastatic niche by inducing tumor deposition of extracellular matrix proteins such as fibronectin that is disrupted by the antifibrotic tyrosine kinase inhibitor (TKI) nintedanib. Our data shed light on the non-cell-autonomous effects of TKIs on metastasis and provide a roadmap for using single-cell and spatial transcriptomics to define the mechanism of action of TKI on metastases in animal models.

Exposure of lung fibroblasts to PM2.5 and lead (Pb) induces fibrosis and apoptosis in alveolar epithelial cells via a paracrine effect

Exposure to fine particulate matter (PM2.5) and heavy metals (HMs) in the air is closely associated with the incidence and exacerbation of pulmonary fibrosis. Although the specific responses of alveolar epithelial cells (AECs) and lung fibroblasts to PM2.5 or HM exposure have been well defined, the cellular responses of lung fibroblasts to PM2.5 or HM exposure and the subsequent interactions with AECs remain poorly investigated. In this study, we demonstrated that human lung fibroblasts exposed to PM2.5 or lead (Pb) induced fibrotic changes and apoptosis in AECs. Lung fibroblasts exposed to PM2.5 induced fibrotic changes in AECs via a paracrine action. We further evaluated the detrimental effects of four HMs (cadmium, lead, arsenic, and manganese) present at the highest levels in the ambient air of South Korea, and investigated their paracrine effects on AECs. We found that long-term (14 passages) exposure to these HMs negatively affected the growth, migration, and survival of lung fibroblasts. Notably, manganese (Mn) significantly upregulated the expression of fibrotic markers with the activation of extracellular signal-regulated kinase (ERK) signaling in lung fibroblasts. However, treatment with conditioned medium (CM) collected from Mn-treated lung fibroblasts did not induce fibrotic changes in AECs. Interestingly, CM from Pb-treated lung fibroblasts significantly upregulated markers for fibrosis and apoptosis in AECs via activation of the ERK signaling pathway. These results suggest that understanding interactions between fibroblasts and AECs may provide useful strategies against PM or HM-induced injuries in alveolar tissue.

Aberrant activation of wound healing programs within the metastatic niche facilitates lung colonization by osteosarcoma cells

PURPOSE

Lung metastasis is responsible for nearly all deaths caused by osteosarcoma, the most common pediatric bone tumor. How malignant bone cells coerce the lung microenvironment to support metastatic growth is unclear. The purpose of this study is to identify metastasis-specific therapeutic vulnerabilities by delineating the cellular and molecular mechanisms underlying osteosarcoma lung metastatic niche formation.

EXPERIMENTAL DESIGN

Using single-cell transcriptomics (scRNA-seq), we characterized genome- and tissue-wide molecular changes induced within lung tissues by disseminated osteosarcoma cells in both immunocompetent murine models of metastasis and patient samples. We confirmed transcriptomic findings at the protein level and determined spatial relationships with multi-parameter immunofluorescence and spatial transcriptomics. Based on these findings, we evaluated the ability of nintedanib, a kinase inhibitor used to treat patients with pulmonary fibrosis, to impair metastasis progression in both immunocompetent murine osteosarcoma and immunodeficient human xenograft models. Single-nucleus and spatial transcriptomics was used to perform molecular pharmacodynamic studies that define the effects of nintedanib on tumor and non-tumor cells within the metastatic microenvironment.

RESULTS

Osteosarcoma cells induced acute alveolar epithelial injury upon lung dissemination. scRNA-seq demonstrated that the surrounding lung stroma adopts a chronic, non-resolving wound-healing phenotype similar to that seen in other models of lung injury. Accordingly, metastasis-associated lung demonstrated marked fibrosis, likely due to the accumulation of pathogenic, pro-fibrotic, partially differentiated epithelial intermediates and macrophages. Our data demonstrated that nintedanib prevented metastatic progression in multiple murine and human xenograft models by inhibiting osteosarcoma-induced fibrosis.

CONCLUSIONS

Fibrosis represents a targetable vulnerability to block the progression of osteosarcoma lung metastasis. Our data support a model wherein interactions between osteosarcoma cells and epithelial cells create a pro-metastatic niche by inducing tumor deposition of extracellular matrix proteins such as fibronectin that is disrupted by the anti-fibrotic TKI nintedanib. Our data shed light on the non-cell autonomous effects of TKIs on metastasis and provide a roadmap for using single-cell and spatial transcriptomics to define the mechanism of action of TKI on metastases in animal models.

Suppression of OGN in lung myofibroblasts attenuates pulmonary fibrosis by inhibiting integrin αv-mediated TGF-β/Smad pathway activation

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) represents a severe and progressive manifestation of idiopathic interstitial pneumonia marked by an uncertain etiology along with an unfavorable prognosis. Osteoglycin (OGN), belonging to the small leucine-rich proteoglycans family, assumes pivotal functions in both tissue formation and damage response. However, the roles and potential mechanisms of OGN in the context of lung fibrosis remain unexplored.

METHODS

The assessment of OGN expression levels in fibrotic lungs was conducted across various experimental lung fibrosis mouse models. To elucidate the effects of OGN on the differentiation of lung myofibroblasts, both OGN knockdown and OGN overexpression were employed in vitro. The expression of integrin αv, along with its colocalization with lysosomes and latency-associated peptide (LAP), was monitored in OGN-knockdown lung myofibroblasts. Furthermore, the role of OGN in lung fibrosis was investigated through OGN knockdown utilizing adeno-related virus serotype 6 (AAV6)-mediated delivery.

RESULTS

OGN exhibited upregulation in both lungs and myofibroblasts across diverse lung fibrosis mouse models. And laboratory experiments in vitro demonstrated that OGN knockdown inhibited the TGF-β/Smad signaling pathway in lung myofibroblasts. Conversely, OGN overexpression promoted TGF-β/Smad pathway in these cells. Mechanistic insights revealed that OGN knockdown facilitated lysosome-mediated degradation of integrin αv while inhibiting its binding to latency-associated peptide (LAP). Remarkably, AAV6-targeted OGN knockdown ameliorated the extent of lung fibrosis in experimental mouse models.

CONCLUSION

Our results indicate that inhibiting OGN signaling could serve as a promising therapeutic way for lung fibrosis.

HMGB1 derived from lung epithelial cells after cobalt nanoparticle exposure promotes the activation of lung fibroblasts

We have previously demonstrated that exposure to cobalt nanoparticles (Nano-Co) caused extensive interstitial fibrosis and inflammatory cell infiltration in mouse lungs. However, the underlying mechanisms of Nano-Co-induced pulmonary fibrosis remain unclear. In this study, we investigated the role of high-mobility group box 1 (HMGB1) in the epithelial cell-fibroblast crosstalk in Nano-Co-induced pulmonary fibrosis. Our results showed that Nano-Co exposure caused remarkable production and release of HMGB1, as well as nuclear accumulation of HIF-1α in human bronchial epithelial cells (BEAS-2B) in a dose- and a time-dependent manner. Pretreatment with CAY10585, an inhibitor against HIF-1α, significantly blocked the overexpression of HMGB1 in cell lysate and the release of HMGB1 in the supernatant of BEAS-2B cells induced by Nano-Co exposure, indicating that Nano-Co exposure induces HIF-1α-dependent HMGB1 overexpression and release. In addition, treatment of lung fibroblasts (MRC-5) with conditioned media from Nano-Co-exposed BEAS-2B cells caused increased RAGE expression, MAPK signaling activation, and enhanced expression of fibrosis-associated proteins, such as fibronectin, collagen 1, and α-SMA. However, conditioned media from Nano-Co-exposed BEAS-2B cells with HMGB1 knockdown had no effects on the activation of MRC-5 fibroblasts. Finally, inhibition of ERK1/2, p38, and JNK all abolished MRC-5 activation induced by conditioned media from Nano-Co-exposed BEAS-2B cells, suggesting that MAPK signaling might be a key downstream signal of HMGB1/RAGE to promote MRC-5 fibroblast activation. These findings have important implications for understanding the pro-fibrotic potential of Nano-Co.

Bone morphogenetic protein 4 ameliorates bleomycin-induced pulmonary fibrosis in mice by repressing NLRP3 inflammasome activation and epithelial-mesenchymal transition

Background

Idiopathic pulmonary fibrosis (IPF) is a progressive and deadly lung disease with limited therapeutic options. Bone morphogenetic protein 4 (BMP4), a multifunctional growth factor that belongs to the transforming growth factor-β superfamily, is able to relieve pulmonary fibrosis in mice; nevertheless, the potential mechanism of action remains largely unknown. Growing evidence supports the notion that reiterant damage to the alveolar epithelial cells (AECs) is usually the "prime mover" for pulmonary fibrosis. Here, we examined the effect and mechanisms of BMP4 on bleomycin (BLM)-induced activation of NLR family pyrin domain containing 3 (NLRP3) inflammasome and epithelial-mesenchymal transition (EMT) in vivo and in vitro.

Methods

The in vivo impact of BMP4 was investigated in a BLM mouse model. Histopathologic changes were analyzed by hematoxylin-eosin (H&E) and Masson's trichrome staining. The NLRP3 inflammasome activation was determined by quantitative real time polymerase chain reaction (qRT-PCR) and immunofluorescence staining. Biomarkers of EMT were measured by qRT-PCR, Western blot and immunofluorescence staining. The in vitro impact of BMP4 on BLM-induced NLRP3 inflammasome activation and EMT was explored in A549 AECs. We also evaluated whether BMP4 inhibited BLM-activated ERK1/2 signaling to address the possible molecular mechanisms.

Results

BMP4 was significantly downregulated in the mouse lungs from BLM-induced pulmonary fibrosis. BMP4+/- mice presented with more severe lung fibrosis in response to BLM, and accelerated NLRP3 inflammasome activation and EMT process compared with that in BMP4+/+ mice. Whereas overexpression of BMP4 by injecting adeno-associated virus (AAV) 9 into mice attenuated BLM-induced fibrotic changes, NLRP3 inflammasome activation, and EMT in the mouse lungs, thus exerting protective efficacy against lung fibrosis. In vitro, BMP4 significantly reduced BLM-induced activation of NLRP3 inflammasome and EMT in human alveolar epithelial A549 cells. Mechanically, BMP4 repressed BLM-induced activation of ERK1/2 signaling in vivo and in vitro, suggesting that ERK1/2 inactivation contributes to BMP4-induced effects on BLM-induced activation of NLRP3 inflammasome and EMT.

Conclusions

Our findings suggest that BMP4 can suppress NLRP3 inflammasome activation and EMT in AECs via inhibition of ERK1/2 signaling pathway, thus has a potential for the treatment of pulmonary fibrosis.

Silica nanoparticles triggered epithelial ferroptosis via miR-21-5p/GCLM signaling to contribute to fibrogenesis in the lungs

The toxicity of silica nanoparticles (SiNPs) to lung is known. We previously demonstrated that exposure to SiNPs promoted pulmonary impairments, but the precise pathogenesis remains elucidated. Ferroptosis has now been identified as a unique form of oxidative cell death, but whether it participated in SiNPs-induced lung injury remains unclear. In this work, we established a rat model with sub-chronic inhalation exposure of SiNPs via intratracheal instillation, and conducted histopathological examination, iron detection, and ferroptosis-related lipid peroxidation and protein assays. Moreover, we evaluated the effect of SiNPs on epithelial ferroptosis, possible mechanisms using in vitro-cultured human bronchial epithelial cells (16HBE), and also assessed the ensuing impact on fibroblast activation for fibrogenesis. Consequently, fibrotic lesions occurred in the rat lungs, concomitantly by enhanced lipid peroxidation, iron overload, and ferroptosis. Consistently, the in vitro data showed SiNPs triggered oxidative stress and caused the accumulation of lipid peroxides, resulting in ferroptosis. Importantly, the mechanistic investigation revealed miR-21-5p as a key player in the epithelial ferroptotic process induced by SiNPs via targeting GCLM for GSH depletion. Of note, ferrostatin-1 could greatly suppress ferroptosis and alleviate epithelial injury and ensuing fibroblast activation by SiNPs. In conclusion, our findings first revealed SiNPs triggered epithelial ferroptosis through miR-21-5p/GCLM signaling and thereby promoted fibroblast activation for fibrotic lesions, and highlighted the therapeutic potential of inhibiting ferroptosis against lung impairments upon SiNPs exposure.

Lung cell transplantation for pulmonary fibrosis

Idiopathic pulmonary fibrosis is a major cause of death with few treatment options. Here, we demonstrate the therapeutic efficacy for lung fibrosis of adult lung cell transplantation using a single-cell suspension of the entire lung in two distinct mouse systems: bleomycin treatment and mice lacking telomeric repeat-binding factor 1 expression in alveolar type 2 (AT2) cells (SPC-Cre TRF1fl/fl), spontaneously developing fibrosis. In both models, the progression of fibrosis was associated with reduced levels of host lung progenitors, enabling engraftment of donor progenitors without any additional conditioning, in contrast to our previous studies. Two months after transplantation, engrafted progenitors expanded to form numerous donor-derived patches comprising AT1 and AT2 alveolar cells, as well as donor-derived mesenchymal and endothelial cells. This lung chimerism was associated with attenuation of fibrosis, as demonstrated histologically, biochemically, by computed tomography imaging, and by lung function measurements. Our study provides a strong rationale for the treatment of lung fibrosis using lung cell transplantation.

Fibroblast Yap/Taz Signaling in Extracellular Matrix Homeostasis and Tissue Fibrosis

Tissue fibrosis represents a complex pathological condition characterized by the excessive accumulation of collagenous extracellular matrix (ECM) components, resulting in impaired organ function. Fibroblasts are central to the fibrotic process and crucially involved in producing and depositing collagen-rich ECM. Apart from their primary function in ECM synthesis, fibroblasts engage in diverse activities such as inflammation and shaping the tissue microenvironment, which significantly influence cellular and tissue functions. This review explores the role of Yes-associated protein (Yap) and Transcriptional co-activator with PDZ-binding motif (Taz) in fibroblast signaling and their impact on tissue fibrosis. Gaining a comprehensive understanding of the intricate molecular mechanisms of Yap/Taz signaling in fibroblasts may reveal novel therapeutic targets for fibrotic diseases.

NR2F2 alleviates pulmonary fibrosis by inhibition of epithelial cell senescence

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, fatal, and aging-associated interstitial lung disease with a poor prognosis and limited treatment options, while the pathogenesis remains elusive. In this study, we found that the expression of nuclear receptor subfamily 2 group F member 2 (NR2F2), a member of the steroid thyroid hormone superfamily of nuclear receptors, was reduced in both IPF and bleomycin-induced fibrotic lungs, markedly in bleomycin-induced senescent epithelial cells. Inhibition of NR2F2 expression increased the expression of senescence markers such as p21 and p16 in lung epithelial cells, and activated fibroblasts through epithelial-mesenchymal crosstalk, inversely overexpression of NR2F2 alleviated bleomycin-induced epithelial cell senescence and inhibited fibroblast activation. Subsequent mechanistic studies revealed that overexpression of NR2F2 alleviated DNA damage in lung epithelial cells and inhibited cell senescence. Adenovirus-mediated Nr2f2 overexpression attenuated bleomycin-induced lung fibrosis and cell senescence in mice. In summary, these data demonstrate that NR2F2 is involved in lung epithelial cell senescence, and targeting NR2F2 may be a promising therapeutic approach against lung cell senescence and fibrosis.

PDE12 disrupts mitochondrial oxidative phosphorylation and mediates mitochondrial dysfunction to induce oral mucosal epithelial barrier damage in oral submucous fibrosis

Oral submucous fibrosis (OSF) is a chronic oral mucosal disease. The pathological changes of OSF include epithelial damage and subepithelial matrix fibrosis. This study aimed to reveal the epithelial injury mechanism of OSF. A histopathological method was used to analyze oral mucosal tissue from OSF patients and OSF rats. The expression of PDE12 in the oral epithelium was analyzed by immunohistochemistry. The epithelial-mesenchymal transition (EMT) and tight junction proteins in arecoline-treated HOKs were explored by western blotting. Epithelial leakage was assessed by transepithelial electrical resistance and lucifer yellow permeability. The expression of PDE12 and the mitochondrial morphology, mitochondrial permeability transition pore opening, mitochondrial membrane potential, and mitochondrial reactive oxygen species (mtROS) were evaluated in arecoline-induced HOKs. Oxidative phosphorylation (OXPHOS) complexes and ATP content were also explored in HOKs. The results showed significant overexpression of PDE12 in oral mucosal tissue from OSF patients and rats. PDE12 was also overexpressed and aggregated in mitochondria in arecoline-induced HOKs, resulting in dysfunction of OXPHOS and impaired mitochondrial function. An EMT, disruption of tight junctions with epithelial leakage, and extracellular matrix remodeling were also observed. PDE12 overexpression induced by PDE12 plasmid transfection enhanced the mtROS level and interfered with occludin protein localization in HOKs. Interestingly, knockdown of PDE12 clearly ameliorated arecoline-induced mitochondrial dysfunction and epithelial barrier dysfunction in HOKs. Therefore, we concluded that overexpression of PDE12 impaired mitochondrial OXPHOS and mitochondrial function and subsequently impaired epithelial barrier function, ultimately leading to OSF. We suggest that PDE12 may be a new potential target against OSF.

Dysregulated bidirectional epithelial-mesenchymal crosstalk: a core determinant of lung fibrosis progression

Progressive lung fibrosis is characterised by dysregulated extracellular matrix (ECM) homeostasis. Understanding of disease pathogenesis remains limited and has prevented the development of effective treatments. While an abnormal wound healing response is strongly implicated in lung fibrosis initiation, factors that determine why fibrosis progresses rather than regular tissue repair occurs are not fully explained. Within human lung fibrosis there is evidence of altered epithelial and mesenchymal lung populations as well as cells undergoing epithelial-mesenchymal transition (EMT), a dynamic and reversible biological process by which epithelial cells lose their cell polarity and down-regulate cadherin-mediated cell-cell adhesion to gain migratory properties. This review will focus upon the role of EMT and dysregulated epithelial-mesenchymal crosstalk in progressive lung fibrosis.

Genistein alleviates pulmonary fibrosis by inactivating lung fibroblasts

Pulmonary fibrosis is a serious lung disease that occurs predominantly in men. Genistein is an important natural soybeanderived phytoestrogen that affects various biological functions, such as cell migration and fibrosis. However, the antifibrotic effects of genistein on pulmonary fibrosis are largely unknown. The antifibrotic effects of genistein were evaluated using in vitro and in vivo models of lung fibrosis. Proteomic data were analyzed using nano-LC-ESI-MS/MS. Genistein significantly reduced transforming growth factor (TGF)-β1-induced expression of collagen type I and α-smooth muscle actin (SMA) in MRC-5 cells and primary fibroblasts from patients with idiopathic pulmonary fibrosis (IPF). Genistein also reduced TGF-β1-induced expression of p-Smad2/3 and p-p38 MAPK in fibroblast models. Comprehensive protein analysis confirmed that genistein exerted an anti-fibrotic effect by regulating various molecular mechanisms, such as unfolded protein response, epithelial mesenchymal transition (EMT), mammalian target of rapamycin complex 1 (mTORC1) signaling, cell death, and several metabolic pathways. Genistein was also found to decrease hydroxyproline levels in the lungs of BLM-treated mice. Genistein exerted an anti-fibrotic effect by preventing fibroblast activation, suggesting that genistein could be developed as a pharmacological agent for the prevention and treatment of pulmonary fibrosis. [BMB Reports 2024; 57(3): 143-148].

The mechanism of gut-lung axis in pulmonary fibrosis

Pulmonary fibrosis (PF) is a terminal change of a lung disease that is marked by damage to alveolar epithelial cells, abnormal proliferative transformation of fibroblasts, excessive deposition of extracellular matrix (ECM), and concomitant inflammatory damage. Its characteristics include short median survival, high mortality rate, and limited treatment effectiveness. More in-depth studies on the mechanisms of PF are needed to provide better treatment options. The idea of the gut-lung axis has emerged as a result of comprehensive investigations into the microbiome, metabolome, and immune system. This theory is based on the material basis of microorganisms and their metabolites, while the gut-lung circulatory system and the shared mucosal immune system act as the connectors that facilitate the interplay between the gastrointestinal and respiratory systems. The emergence of a new view of the gut-lung axis is complementary and cross-cutting to the study of the mechanisms involved in PF and provides new ideas for its treatment. This article reviews the mechanisms involved in PF, the gut-lung axis theory, and the correlation between the two. Exploring the gut-lung axis mechanism and treatments related to PF from the perspectives of microorganisms, microbial metabolites, and the immune system. The study of the gut-lung axis and PF is still in its early stages. This review systematically summarizes the mechanisms of PF related to the gut-lung axis, providing ideas for subsequent research and treatment of related mechanisms.

Therapeutic Approaches for the Treatment of Interstitial Lung Disease: An Exploratory Review on Molecular Mechanisms

BACKGROUND

Interstitial Lung Diseases (ILDs) are characterized by shortness of breath caused by alveolar wall inflammation and/or fibrosis.

OBJECTIVE

Our review aims to study the depth of various variants of ILD, diagnostic procedures, pathophysiology, molecular dysfunction and regulation, subject and objective assessment techniques, pharmacological intervention, exercise training and various modes of delivery for rehabilitation.

METHOD

Articles are reviewed from PubMed and Scopus and search engines.

RESULTS

ILD is a rapidly progressing disease with a high mortality rate. Each variant has its own set of causal agents and expression patterns. Patients often find it challenging to self-manage due to persistent symptoms and a rapid rate of worsening. The present review elaborated on the pathophysiology, risk factors, molecular mechanisms, diagnostics, and therapeutic approaches for ILD will guide future requirements in the quest for innovative and tailored ILD therapies at the molecular and cellular levels.

CONCLUSION

The review highlights the rationale for conventional and novel therapeutic approaches for better management of ILD.

The Plastic Interplay between Lung Regeneration Phenomena and Fibrotic Evolution: Current Challenges and Novel Therapeutic Perspectives

Interstitial lung diseases (ILDs) are a heterogeneous group of pulmonary disorders characterized by variable degrees of inflammation, interstitial thickening, and fibrosis leading to distortion of the pulmonary architecture and gas exchange impairment. Among them, idiopathic pulmonary fibrosis (IPF) displays the worst prognosis. The only therapeutic options consist of the two antifibrotic drugs, pirfenidone and nintedanib, which limit fibrosis progression but do not reverse the lung damage. The shift of the pathogenetic paradigm from inflammatory disease to epithelium-derived disease has definitively established the primary role of type II alveolar cells, which lose their epithelial phenotype and acquire a mesenchymal phenotype with production of collagen and extracellular matrix (EMC) deposition. Some predisposing environmental and genetic factors (e.g., smoke, pollution, gastroesophageal reflux, variants of telomere and surfactant genes) leading to accelerated senescence set a pro-fibrogentic microenvironment and contribute to the loss of regenerative properties of type II epithelial cells in response to pathogenic noxae. This review provides a complete overview of the different pathogenetic mechanisms leading to the development of IPF. Then, we summarize the currently approved therapies and the main clinical trials ongoing. Finally, we explore the potentialities offered by agents not only interfering with the processes of fibrosis but also restoring the physiological properties of alveolar regeneration, with a particular focus on potentialities and concerns about cell therapies based on mesenchymal stem cells (MSCs), whose anti-inflammatory and immunomodulant properties have been exploited in other fibrotic diseases, such as graft versus host disease (GVHD) and COVID-19-related ARDS.

3D Airway Epithelial-Fibroblast Biomimetic Microfluidic Platform to Unravel Engineered Nanoparticle-Induced Acute Stress Responses as Exposome Determinants

Insights into how biological systems respond to high- and low-dose acute environmental stressors are a fundamental aspect of exposome research. However, studying the impact of low-level environmental exposure in conventional in vitro settings is challenging. This study employed a three-dimensional (3D) biomimetic microfluidic lung-on-chip (μLOC) platform and RNA-sequencing to examine the effects of two model anthropogenic engineered nanoparticles (NPs): zinc oxide nanoparticles (Nano-ZnO) and copier center nanoparticles (Nano-CCP). The airway epithelium exposed to these NPs exhibited dose-dependent increases in cytotoxicity and barrier dysregulation (dominance of the external exposome). Interestingly, even nontoxic and low-level exposure (10 μg/mL) of the epithelium compartment to Nano-ZnO triggered chemotaxis of lung fibroblasts toward the epithelium. An increase in α smooth muscle actin (α-SMA) expression and contractile activity was also observed in these cells, indicating a bystander-like adaptive response (dominance of internal exposome). Further bioinformatics and network analysis showed that a low-dose Nano-ZnO significantly induced a robust transcriptomic response and upregulated several hub genes associated with the development of lung fibrosis. We propose that Nano-ZnO, even at a no observable effect level (NOEL) dose according to conventional standards, can function as a potent nanostressor to disrupt airway epithelium homeostasis. This leads to a cascade of profibrotic events in a cross-tissue compartment fashion. Our findings offer new insights into the early acute events of respiratory harm associated with environmental NPs exposure, paving the way for better exposomic understanding of this emerging class of anthropogenic nanopollutants.

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.

A Phase I Study of TRK-250, a Novel siRNA-Based Oligonucleotide, in Patients with Idiopathic Pulmonary Fibrosis

Purpose: TRK-250 is a novel single-stranded oligonucleotide carrying a human Transforming growth factor-beta 1-targeting siRNA motif tethered by two proline linkers. Nonclinical studies have shown that TRK-250 may have potency to prevent the progression of pulmonary fibrosis. Herein, a phase I study was conducted to investigate the safety and pharmacokinetics (PKs) of TRK-250 in patients with idiopathic pulmonary fibrosis (IPF). Method: In the phase I study, 34 IPF patients were partially randomized to receive a placebo or TRK-250 in 4 single doses of 2, 10, 30, and 60 mg or multiple rising doses of 10, 30, and 60 mg once per week for 4 weeks by oral inhalation. For both the single- and multiple-dose studies, the primary endpoint was safety, and the secondary endpoint was PKs. Result: In all IPF patients who orally inhaled TRK-250, no significant drug-related adverse events (AEs) were observed. The AEs were mild or moderate, except for one severe case with acute exacerbation. One of the more common AEs was coughing. One patient discontinued treatment before the last dose because of coughing. There were no medically important findings related to safety endpoints based on clinical laboratory data (clinical chemistry, hematology, or urinalysis), vital signs data, electrocardiogram data, physical examination findings, pulse oximetry data, spirometry data, or diffusing capacity of the lung for carbon monoxide data. All the bioanalytical results of PKs in the blood were below the lower limit of quantification. Conclusions: Both the single and multiple doses of TRK-250 were safe and well tolerated in this first study done in IPF patients. Furthermore, TRK-250 was not detected in the systemic circulation following inhalation, indicating low or virtually nonexistent systemic exposure. This study is registered at ClinicalTrials.gov with identifier number NCT03727802.

In vitro co-culture studies and the crucial role of fibroblast-immune cell crosstalk in IPF pathogenesis

IPF is a fatal lung disease characterized by intensive remodeling of lung tissue leading to respiratory failure. The remodeling in IPF lungs is largely characterized by uncontrolled fibrosis. Fibroblasts and their contractile phenotype the myofibroblast are the main cell types responsible for typical wound healing responses, however in IPF, these responses are aberrant and result in the overactivation of fibroblasts which contributes to the inelasticity of the lung leading to a decrease in lung function. The specific mechanisms behind IPF pathogenesis have been elusive, but recently the innate and adaptive immunity have been implicated in the fibrotic processes of the disease. In connection with this, several in vitro co-culture models have been used to investigate the specific interactions occurring between fibroblasts and immune cells and how this contributes to the pathobiology of IPF. In this review, we discuss the in vitro models that have been used to examine the abnormal interactions between fibroblasts and cells of the innate and adaptive immune system, and how these contribute to the fibrotic processes in the lungs of IPF patients.

New aspects of the epigenetic regulation of EMT related to pulmonary fibrosis

Pulmonary fibrosis is a chronic and progressive fibrotic disease that results in impaired gas exchange, ventilation, and eventual death. The pro-fibrotic environment is instigated by various factors, leading to the transformation of epithelial cells into myofibroblasts and/or fibroblasts that trigger fibrosis. Epithelial mesenchymal transition (EMT) is a biological process that plays a critical role in the pathogenesis of pulmonary fibrosis. Epigenetic regulation of tissue-stromal crosstalk involving DNA methylation, histone modifications, non-coding RNA, and chromatin remodeling plays a key role in the control of EMT. The review investigates the epigenetic regulation of EMT and its significance in pulmonary fibrosis.

Connexin-43 hemichannels orchestrate NOD-like receptor protein-3 (NLRP3) inflammasome activation and sterile inflammation in tubular injury

BACKGROUND

Without a viable cure, chronic kidney disease is a global health concern. Inflammatory damage in and around the renal tubules dictates disease severity and is contributed to by multiple cell types. Activated in response to danger associated molecular patterns (DAMPs) including ATP, the NOD-like receptor protein-3 (NLRP3) inflammasome is integral to this inflammation. In vivo, we have previously observed that increased expression of Connexin 43 (Cx43) is linked to inflammation in chronic kidney disease (CKD) whilst in vitro studies in human proximal tubule cells highlight a role for aberrant Cx43 hemichannel mediated ATP release in tubule injury. A role for Cx43 hemichannels in priming and activation of the NLRP3 inflammasome in tubule epithelial cells remains to be determined.

METHODS

Using the Nephroseq database, analysis of unpublished transcriptomic data, examined gene expression and correlation in human CKD. The unilateral ureteral obstruction (UUO) mouse model was combined with genetic (tubule-specific Cx43 knockout) and specific pharmacological blockade of Cx43 (Peptide5), to explore a role for Cx43-hemichannels in tubule damage. Human primary tubule epithelial cells were used as an in vitro model of CKD.

RESULTS

Increased Cx43 and NLRP3 expression correlates with declining glomerular filtration rate and increased proteinuria in biopsies isolated from patients with CKD. Connexin 43-tubule deletion prior to UUO protected against tubular injury, increased expression of proinflammatory molecules, and significantly reduced NLRP3 expression and downstream signalling mediators. Accompanied by a reduction in F4/80 macrophages and fibroblast specific protein (FSP1+) fibroblasts, Cx43 specific hemichannel blocker Peptide5 conferred similar protection in UUO mice. In vitro, Peptide5 determined that increased Cx43-hemichannel activity primes and activates the NLRP3 inflammasome via ATP-P2X7 receptor signalling culminating in increased secretion of chemokines and cytokines, each of which are elevated in individuals with CKD. Inhibition of NLRP3 and caspase 1 similarly decreased markers of tubular injury, whilst preventing the perpetual increase in Cx43-hemichannel activity.

CONCLUSION

Aberrant Cx43-hemichannel activity in kidney tubule cells contributes to tubule inflammation via activation of the NLRP3 inflammasome and downstream paracrine mediated cell signalling. Use of hemichannel blockers in targeting Cx43-hemichannels is an attractive future therapeutic target to slow or prevent disease progression in CKD. Video Abstract.

Inhibitory Effects of Epithelial Cells on Fibrosis Mechanics of Microtissue and Their Spatiotemporal Dependence on the Epithelial-Fibroblast Interaction

Cell-generated contraction force is the primary physical drive for fibrotic densification of biological tissues. Previous studies using two-dimensional culture models have shown that epithelial cells inhibit the myofibroblast-derived contraction force via the regulation of the fibroblast/myofibroblast transition (FMT). However, it remains unclear how epithelial cells interact with fibroblasts and myofibroblasts to determine the mechanical consequences and spatiotemporal regulation of fibrosis development. In this study, we established a three-dimensional microtissue model using an NIH/3T3 fibroblast-laden collagen hydrogel, incorporated with a microstring-based force sensor, to assess fibrosis mechanics. When Madin-Darby canine kidney epithelial cells were cocultured on the microtissue's surface, the densification, stiffness, and contraction force of the microtissue greatly decreased compared to the monocultured microtissue without epithelial cells. The key fibrotic features, such as enhanced protein expression of α-smooth muscle actin, fibronectin, and collagen indicating FMT and matrix deposition, respectively, were also significantly reduced. The antifibrotic effects of epithelial cells on the microtissue were dependent on the intercellular signaling molecule prostaglandin E2 (PGE2) with an effective concentration of 10 μM and their proximity to the fibroblasts, indicating paracrine cellular signaling between the two types of cells during tissue fibrosis. The effect of PGE2 on microtissue contraction was also dependent on the time point when PGE2 was delivered or blocked, suggesting that the presence of epithelial cells at an early stage is critical for preventing or treating advanced fibrosis. Taken together, this study provides insights into the spatiotemporal regulation of mechanical properties of fibrosis by epithelial cells, and the cocultured microtissue model incorporated with a real-time and sensitive force sensor will be a suitable system for evaluating fibrosis and drug screening.

Fibroblast activation in response to TGFβ1 is modulated by co-culture with endothelial cells in a vascular organ-on-chip platform

Background: Tissue fibrosis is a major healthcare burden that affects various organs in the body for which no effective treatments exist. An underlying, emerging theme across organs and tissue types at early stages of fibrosis is the activation of pericytes and/or fibroblasts in the perivascular space. In hepatic tissue, it is well known that liver sinusoidal endothelial cells (EC) help maintain the quiescence of stellate cells, but whether this phenomenon holds true for other endothelial and perivascular cell types is not well studied. Methods: The goal of this work was to develop an organ-on-chip microvascular model to study the effect of EC co-culture on the activation of perivascular cells perturbed by the pro-fibrotic factor TGFβ1. A high-throughput microfluidic platform, PREDICT96, that was capable of imparting physiologically relevant fluid shear stress on the cultured endothelium was utilized. Results: We first studied the activation response of several perivascular cell types and selected a cell source, human dermal fibroblasts, that exhibited medium-level activation in response to TGFβ1. We also demonstrated that the PREDICT96 high flow pump triggered changes in select shear-responsive factors in human EC. We then found that the activation response of fibroblasts was significantly blunted in co-culture with EC compared to fibroblast mono-cultures. Subsequent studies with conditioned media demonstrated that EC-secreted factors play at least a partial role in suppressing the activation response. A Luminex panel and single cell RNA-sequencing study provided additional insight into potential EC-derived factors that could influence fibroblast activation. Conclusion: Overall, our findings showed that EC can reduce myofibroblast activation of perivascular cells in response to TGFβ1. Further exploration of EC-derived factors as potential therapeutic targets in fibrosis is warranted.

Innovative Pre-Clinical Data Using Peptides to Intervene in the Evolution of Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive, relentless, and deadly disease. Little is known about its pathogenetic mechanisms; therefore, developing efficient pharmacological therapies is challenging. This work aimed to apply a therapeutic alternative using immunomodulatory peptides in a chronic pulmonary fibrosis murine model. BALB/c mice were intratracheally instilled with bleomycin (BLM) and followed for 30 days. The mice were treated with the immune modulatory peptides ToAP3 and ToAP4 every three days, starting on the 5th day post-BLM instillation. ELISA, qPCR, morphology, and respiratory function analyses were performed. The treatment with both peptides delayed the inflammatory process observed in the non-treated group, which showed a fibrotic process with alterations in the production of collagen I, III, and IV that were associated with significant alterations in their ventilatory mechanics. The ToAP3 and ToAP4 treatments, by lung gene modulation patterns, indicated that distinct mechanisms determine the action of peptides. Both peptides controlled the experimental IPF, maintaining the tissue characteristics and standard function properties and regulating fibrotic-associated cytokine production. Data obtained in this work show that the immune response regulation by ToAP3 and ToAP4 can control the alterations that cause the fibrotic process after BLM instillation, making both peptides potential therapeutic alternatives and/or adjuvants for IPF.

Utilization of endogenous albumin trafficking pathways in the lungs has potential to modestly increase the lung interstitial access and absorption of drug delivery systems after inhaled administration

OBJECTIVES

Drug delivery systems typically show limited access to the lung interstitium and absorption after pulmonary delivery. The aim of this work was to undertake a proof-of-concept investigation into the potential of employing endogenous albumin and albumin absorption mechanisms in the lungs to improve lung interstitial access and absorption of inhaled drug delivery systems that bind albumin.

METHODS

The permeability of human albumin (HSA) through monolayers of primary human alveolar epithelia, small airway epithelia, and microvascular endothelium were investigated. The pulmonary pharmacokinetics of bovine serum albumin (BSA) was also investigated in efferent caudal mediastinal lymph duct-cannulated sheep after inhaled aerosol administration.

RESULTS

Membrane permeability coefficient values (Papp) of HSA increased in the order alveolar epithelia

CONCLUSION

Drug delivery systems that bind endogenous albumin may show a modest increase in lung permeability and absorption after inhaled delivery compared to systems that do not efficiently bind albumin.

Collapse

Key Words

• Albumin
• inhaled
• lung permeability
• nebulized
• pharmacokinetics
• sheep

Collapse

MESH Headings

• Humans
• Animals
• Sheep
• Lung/metabolism
• Albumins/metabolism
• Drug Delivery Systems
• Aerosols
• Lymph/metabolism

Collapse

Grants Collapse

Affiliation(s)

Jibriil P Ibrahim School of Biomedical Sciences, University of Queensland, St Lucia, QLD, Australia
Neville J Butcher School of Biomedical Sciences, University of Queensland, St Lucia, QLD, Australia
Ashok Kothapalli School of Biomedical Sciences, University of Queensland, St Lucia, QLD, Australia
Christopher N Subasic School of Biomedical Sciences, University of Queensland, St Lucia, QLD, Australia
Joanne T Blanchfield School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, QLD, Australia
Andrew K Whittaker Australian Institute of Bioengineering and Nanotechnology, University of Queensland, St Lucia, QLD, Australia Australian Research Council Centre of Excellence for Green Electrochemical Transformation of Carbon Dioxide, University of Queensland, St Lucia, QLD, Australia
Michael R Whittaker Drug Delivery Disposition Dynamics, Monash Institute of Pharmaceutical Sciences, Parkville, VIC, Australia
Lisa M Kaminskas School of Biomedical Sciences, University of Queensland, St Lucia, QLD, Australia

Collapse

Myocardin-related transcription factor contributes to renal fibrosis through the regulation of extracellular microenvironment surrounding fibroblasts

Fibroblast accumulation and extracellular matrix (ECM) deposition are common critical steps for the progression of organ fibrosis, but the precise molecular mechanisms remain to be fully investigated. We have previously demonstrated that lysophosphatidic acid contributes to organ fibrosis through the production of connective tissue growth factor (CTGF) via actin cytoskeleton-dependent signaling, myocardin-related transcription factor family (MRTF) consisting of MRTF-A and MRTF-B-serum response factor (SRF) pathway. In this study, we investigated the role of the MRTF-SRF pathway in the development of renal fibrosis, focusing on the regulation of ECM-focal adhesions (FA) in renal fibroblasts. Here we showed that both MRTF-A and -B were required for the expressions of ECM-related molecules such as lysyl oxidase family members, type I procollagen and fibronectin in response to transforming growth factor (TGF)-β1 . TGF-β1 -MRTF-SRF pathway induced the expressions of various components of FA such as integrin α subunits (αv , α2 , α11 ) and β subunits (β1 , β3 , β5 ) as well as integrin-linked kinase (ILK). On the other hand, the blockade of ILK suppressed TGF-β1 -induced MRTF-SRF transcriptional activity, indicating a mutual relationship between MRTF-SRF and FA. Myofibroblast differentiation along with CTGF expression was also dependent on MRTF-SRF and FA components. Finally, global MRTF-A deficient and inducible fibroblast-specific MRTF-B deficient mice (MRTF-AKO BiFBKO mice) are protected from renal fibrosis with adenine administration. Renal expressions of ECM-FA components and CTGF as well as myofibroblast accumulation were suppressed in MRTF-AKO BiFBKO mice. These results suggest that the MRTF-SRF pathway might be a therapeutic target for renal fibrosis through the regulation of components forming ECM-FA in fibroblasts.

Multiple Fibroblast Subtypes Contribute to Matrix Deposition in Pulmonary Fibrosis

Progressive pulmonary fibrosis results from a dysfunctional tissue repair response and is characterized by fibroblast proliferation, activation, and invasion and extracellular matrix accumulation. Lung fibroblast heterogeneity is well recognized. With single-cell RNA sequencing, fibroblast subtypes have been reported by recent studies. However, the roles of fibroblast subtypes in effector functions in lung fibrosis are not well understood. In this study, we incorporated the recently published single-cell RNA-sequencing datasets on murine lung samples of fibrosis models and human lung samples of fibrotic diseases and analyzed fibroblast gene signatures. We identified and confirmed the novel fibroblast subtypes we reported recently across all samples of both mouse models and human lung fibrotic diseases, including idiopathic pulmonary fibrosis, systemic sclerosis-associated interstitial lung disease, and coronavirus disease (COVID-19). Furthermore, we identified specific cell surface proteins for each fibroblast subtype through differential gene expression analysis, which enabled us to isolate primary cells representing distinct fibroblast subtypes by flow cytometry sorting. We compared matrix production, including fibronectin, collagen, and hyaluronan, after profibrotic factor stimulation and assessed the invasive capacity of each fibroblast subtype. Our results suggest that in addition to myofibroblasts, lipofibroblasts and Ebf1+ (Ebf transcription factor 1+) fibroblasts are two important fibroblast subtypes that contribute to matrix deposition and also have enhanced invasive, proliferative, and contraction phenotypes. The histological locations of fibroblast subtypes are identified in healthy and fibrotic lungs by these cell surface proteins. This study provides new insights to inform approaches to targeting lung fibroblast subtypes to promote the development of therapeutics for lung fibrosis.

Novel pirfenidone derivatives: synthesis and biological evaluation

In order to discover novel anti-pulmonary fibrosis agents, a series of novel pirfenidone derivatives were designed and synthesized. All compounds were investigated for their anti-pulmonary activity and characterized by 13C and 1H nuclear magnetic resonance and high-resolution mass spectrometry. Preliminary studies on their biological activity showed that all target compounds showed different degrees of inhibition on pulmonary fibrosis, and most of the derivatives were significantly better than pirfenidone.

Role of heparanase in ARDS through autophagy and exosome pathway (review)

Acute respiratory distress syndrome (ARDS) is the most common respiratory disease in ICU. Although there are many treatment and support methods, the mortality rate is still high. The main pathological feature of ARDS is the damage of pulmonary microvascular endothelium and alveolar epithelium caused by inflammatory reaction, which may lead to coagulation system disorder and pulmonary fibrosis. Heparanase (HPA) plays an significant role in inflammation, coagulation, fibrosis. It is reported that HPA degrades a large amount of HS in ARDS, leading to the damage of endothelial glycocalyx and inflammatory factors are released in large quantities. HPA can aggrandize the release of exosomes through syndecan-syntenin-Alix pathway, leading to a series of pathological reactions; at the same time, HPA can cause abnormal expression of autophagy. Therefore, we speculate that HPA promotes the occurrence and development of ARDS through exosomes and autophagy, which leads to a large amount of release of inflammatory factors, coagulation disorder and pulmonary fibrosis. This article mainly describes the mechanism of HPA on ARDS.

Interleukin-11 disrupts alveolar epithelial progenitor function

Background

Interleukin-11 (IL-11) is linked to the pathogenesis of idiopathic pulmonary fibrosis (IPF), since IL-11 induces myofibroblast differentiation and stimulates their excessive collagen deposition in the lung. In IPF there is disrupted alveolar structural architecture, yet the effect of IL-11 on the dysregulated alveolar repair remains to be elucidated.

Methods

We hypothesised that epithelial-fibroblast communication associated with lung repair is disrupted by IL-11. Thus, we studied whether IL-11 affects the repair responses of alveolar lung epithelium using mouse lung organoids and precision-cut lung slices (PCLS). Additionally, we assessed the anatomical distribution of IL-11 and IL-11 receptor (IL-11R) in human control and IPF lungs using immunohistochemistry.

Results

IL-11 protein was observed in airway epithelium, macrophages and in IPF lungs, also in areas of alveolar type 2 (AT2) cell hyperplasia. IL-11R staining was predominantly present in smooth muscle and macrophages. In mouse organoid co-cultures of epithelial cells with lung fibroblasts, IL-11 decreased organoid number and reduced the fraction of Prosurfactant Protein C-expressing organoids, indicating dysfunctional regeneration initiated by epithelial progenitors. In mouse PCLS exposed to IL-11, ciliated cell markers were increased. The response of primary human fibroblasts to IL-11 on gene expression level was minimal, though bulk RNA-sequencing revealed IL-11 modulated various processes which are associated with IPF, including unfolded protein response, glycolysis and Notch signalling.

Conclusions

IL-11 disrupts alveolar epithelial regeneration by inhibiting progenitor activation and suppressing the formation of mature alveolar epithelial cells. Evidence for a contribution of dysregulated fibroblast-epithelial communication to this process is limited.

Derrone Targeting the TGF Type 1 Receptor Kinase Improves Bleomycin-Mediated Pulmonary Fibrosis through Inhibition of Smad Signaling Pathway

Transforming growth factor-β (TGF-β) has a strong impact on the pathogenesis of pulmonary fibrosis. Therefore, in this study, we investigated whether derrone promotes anti-fibrotic effects on TGF-β1-stimulated MRC-5 lung fibroblast cells and bleomycin-induced lung fibrosis. Long-term treatment with high concentrations of derrone increased the cytotoxicity of MRC-5 cells; however, substantial cell death was not observed at low concentrations of derrone (below 0.05 μg/mL) during a three-day treatment. In addition, derrone significantly decreased the expressions of TGF-β1, fibronectin, elastin, and collagen1α1, and these decreases were accompanied by downregulation of α-SMA expression in TGF-β1-stimulated MRC-5 cells. Severe fibrotic histopathological changes in infiltration, alveolar congestion, and alveolar wall thickness were observed in bleomycin-treated mice; however, derrone supplementation significantly reduced these histological deformations. In addition, intratracheal administration of bleomycin resulted in lung collagen accumulation and high expression of α-SMA and fibrotic genes-including TGF-β1, fibronectin, elastin, and collagen1α1-in the lungs. However, fibrotic severity in intranasal derrone-administrated mice was significantly less than that of bleomycin-administered mice. Molecular docking predicted that derrone potently fits into the ATP-binding pocket of the TGF-β receptor type 1 kinase domain with stronger binding scores than ATP. Additionally, derrone inhibited TGF-β1-induced phosphorylation and nuclear translocations of Smad2/3. Overall, derrone significantly attenuated TGF-β1-stimulated lung inflammation in vitro and bleomycin-induced lung fibrosis in a murine model, indicating that derrone may be a promising candidate for preventing pulmonary fibrosis.

Mesenchymal cells in the Lung: Evolving concepts and their role in fibrosis

Mesenchymal cells in the lung are crucial during development, but also contribute to the pathogenesis of fibrotic disorders, including idiopathic pulmonary fibrosis (IPF), the most common and deadly form of fibrotic interstitial lung diseases. Originally thought to behave as supporting cells for the lung epithelium and endothelium with a singular function of producing basement membrane, mesenchymal cells encompass a variety of cell types, including resident fibroblasts, lipofibroblasts, myofibroblasts, smooth muscle cells, and pericytes, which all occupy different anatomic locations and exhibit diverse homeostatic functions in the lung. During injury, each of these subtypes demonstrate remarkable plasticity and undergo varying capacity to proliferate and differentiate into activated myofibroblasts. Therefore, these cells secrete high levels of extracellular matrix (ECM) proteins and inflammatory cytokines, which contribute to tissue repair, or in pathologic situations, scarring and fibrosis. Whereas epithelial damage is considered the initial trigger that leads to lung injury, lung mesenchymal cells are recognized as the ultimate effector of fibrosis and attempts to better understand the different functions and actions of each mesenchymal cell subtype will lead to a better understanding of why fibrosis develops and how to better target it for future therapy. This review summarizes current findings related to various lung mesenchymal cells as well as signaling pathways, and their contribution to the pathogenesis of pulmonary fibrosis.

p53 and Myofibroblast Apoptosis in Organ Fibrosis

Organ fibrosis represents a dysregulated, maladaptive wound repair response that results in progressive disruption of normal tissue architecture leading to detrimental deterioration in physiological function, and significant morbidity/mortality. Fibrosis is thought to contribute to nearly 50% of all deaths in the Western world with current treatment modalities effective in slowing disease progression but not effective in restoring organ function or reversing fibrotic changes. When physiological wound repair is complete, myofibroblasts are programmed to undergo cell death and self-clearance, however, in fibrosis there is a characteristic absence of myofibroblast apoptosis. It has been shown that in fibrosis, myofibroblasts adopt an apoptotic-resistant, highly proliferative phenotype leading to persistent myofibroblast activation and perpetuation of the fibrotic disease process. Recently, this pathological adaptation has been linked to dysregulated expression of tumour suppressor gene p53. In this review, we discuss p53 dysregulation and apoptotic failure in myofibroblasts and demonstrate its consistent link to fibrotic disease development in all types of organ fibrosis. An enhanced understanding of the role of p53 dysregulation and myofibroblast apoptosis may aid in future novel therapeutic and/or diagnostic strategies in organ fibrosis.

Comparing species-different responses in pulmonary fibrosis research: Current understanding of in vitro lung cell models and nanomaterials

Pulmonary fibrosis (PF) is a chronic, irreversible lung disease that is typically fatal and characterized by an abnormal fibrotic response. As a result, vast areas of the lungs are gradually affected, and gas exchange is impaired, making it one of the world's leading causes of death. This can be attributed to a lack of understanding of the onset and progression of the disease, as well as a poor understanding of the mechanism of adverse responses to various factors, such as exposure to allergens, nanomaterials, environmental pollutants, etc. So far, the most frequently used preclinical evaluation paradigm for PF is still animal testing. Nonetheless, there is an urgent need to understand the factors that induce PF and find novel therapeutic targets for PF in humans. In this regard, robust and realistic in vitro fibrosis models are required to understand the mechanism of adverse responses. Over the years, several in vitro and ex vivo models have been developed with the goal of mimicking the biological barriers of the lung as closely as possible. This review summarizes recent progress towards the development of experimental models suitable for predicting fibrotic responses, with an emphasis on cell culture methods, nanomaterials, and a comparison of results from studies using cells from various species.

Loss of IGFBP2 mediates alveolar type 2 cell senescence and promotes lung fibrosis

Accumulation of senescent cells contributes to age-related diseases including idiopathic pulmonary fibrosis (IPF). Insulin-like growth factor binding proteins (IGFBPs) regulate many biological processes; however, the functional contributions of IGFBP2 in lung fibrosis remain largely unclear. Here, we report that intranasal delivery of recombinant IGFBP2 protects aged mice from weight loss and demonstrated antifibrotic effects after bleomycin lung injury. Notably, aged human-Igfbp2 transgenic mice reveal reduced senescence and senescent-associated secretory phenotype factors in alveolar epithelial type 2 (AEC2) cells and they ameliorated bleomycin-induced lung fibrosis. Finally, we demonstrate that IGFBP2 expression is significantly suppressed in AEC2 cells isolated from fibrotic lung regions of patients with IPF and/or pulmonary hypertension compared with patients with hypersensitivity pneumonitis and/or chronic obstructive pulmonary disease. Altogether, our study provides insights into how IGFBP2 regulates AEC2-cell-specific senescence and that restoring IGFBP2 levels in fibrotic lungs can prove effective for patients with IPF.

A2B Adenosine Receptor in Idiopathic Pulmonary Fibrosis: Pursuing Proper Pit Stop to Interfere with Disease Progression

Purine nucleotides and nucleosides are involved in various human physiological and pathological mechanisms. The pathological deregulation of purinergic signaling contributes to various chronic respiratory diseases. Among the adenosine receptors, A2B has the lowest affinity such that it was long considered to have little pathophysiological significance. Many studies suggest that A2BAR plays protective roles during the early stage of acute inflammation. However, increased adenosine levels during chronic epithelial injury and inflammation might activate A2BAR, resulting in cellular effects relevant to the progression of pulmonary fibrosis.

NF-κB drives epithelial-mesenchymal mechanisms of lung fibrosis in a translational lung cell model

In the progression phase of idiopathic pulmonary fibrosis (IPF), the normal alveolar structure of the lung is lost and replaced by remodeled fibrotic tissue and by bronchiolized cystic airspaces. Although these are characteristic features of IPF, knowledge of specific interactions between these pathological processes is limited. Here, the interaction of lung epithelial and lung mesenchymal cells was investigated in a coculture model of human primary airway epithelial cells (EC) and lung fibroblasts (FB). Single-cell RNA sequencing revealed that the starting EC population was heterogenous and enriched for cells with a basal cell signature. Furthermore, fractions of the initial EC and FB populations adopted distinct pro-fibrotic cell differentiation states upon cocultivation, resembling specific cell populations that were previously identified in lungs of patients with IPF. Transcriptomic analysis revealed active NF-κB signaling early in the cocultured EC and FB, and the identified NF-κB expression signatures were found in "HAS1 High FB" and "PLIN2+ FB" populations from IPF patient lungs. Pharmacological blockade of NF-κB signaling attenuated specific phenotypic changes of EC and prevented FB-mediated interleukin-6, interleukin-8, and CXC chemokine ligand 6 cytokine secretion, as well as collagen α-1(I) chain and α-smooth muscle actin accumulation. Thus, we identified NF-κB as a potential mediator, linking epithelial pathobiology with fibrogenesis.

Optimal control of TGF-β to prevent formation of pulmonary fibrosis

In this paper, three optimal control problems are proposed to prevent forming lung fibrosis while control is transforming growth factor-β (TGF-β) in the myofibroblast diffusion process. Two diffusion equations for fibroblast and myofibroblast are mathematically formulated as the system's dynamic, while different optimal control model problems are proposed to find the optimal TGF-β. During solving the first optimal control problem with the regulator objection function, it is understood that the control function gets unexpected negative values. Thus, in the second optimal control problem, for the control function, the non-negative constraint is imposed. This problem is solved successfully using the extended canonical Hamiltonian equations with no flux boundary conditions. Pontryagin's minimum principle is used to solve the related optimal control problems successfully. In the third optimal control problem, the fibroblast equation is added to a dynamic system consisting of the partial differential equation. The two-dimensional diffusion equations for fibroblast and myofibroblast are transferred to a system of ordinary differential equations using the central finite differences explicit method. Three theorems and two propositions are proved using extended Pontryagin's minimum principle and the extended Hamiltonian equations. Numerical results are given. We believe that this optimal strategy can help practitioners apply some medication to reduce the TGF-β in preventing the formation of pulmonary fibrosis.

Bone morphogenetic protein 4 inhibits pulmonary fibrosis by modulating cellular senescence and mitophagy in lung fibroblasts

BACKGROUND

Accumulation of myofibroblasts is critical to fibrogenesis in idiopathic pulmonary fibrosis (IPF). Senescence and insufficient mitophagy in fibroblasts contribute to their differentiation into myofibroblasts, thereby promoting the development of lung fibrosis. Bone morphogenetic protein 4 (BMP4), a multifunctional growth factor, is essential for the early stage of lung development; however, the role of BMP4 in modulating lung fibrosis remains unknown.

METHODS

The aim of this study was to evaluate the role of BMP4 in lung fibrosis using BMP4-haplodeleted mice, BMP4-overexpressed mice, primary lung fibroblasts and lung samples from patients with IPF.

RESULTS

BMP4 expression was downregulated in IPF lungs and fibroblasts compared to control individuals, negatively correlated with fibrotic genes, and BMP4 decreased with transforming growth factor (TGF)-β1 stimulation in lung fibroblasts in a time- and dose-dependent manner. In mice challenged with bleomycin, BMP4 haploinsufficiency perpetuated activation of lung myofibroblasts and caused accelerated lung function decline, severe fibrosis and mortality. BMP4 overexpression using adeno-associated virus 9 vectors showed preventative and therapeutic efficacy against lung fibrosis. In vitro, BMP4 attenuated TGF-β1-induced fibroblast-to-myofibroblast differentiation and extracellular matrix (ECM) production by reducing impaired mitophagy and cellular senescence in lung fibroblasts. Pink1 silencing by short-hairpin RNA transfection abolished the ability of BMP4 to reverse the TGF-β1-induced myofibroblast differentiation and ECM production, indicating dependence on Pink1-mediated mitophagy. Moreover, the inhibitory effect of BMP4 on fibroblast activation and differentiation was accompanied with an activation of Smad1/5/9 signalling and suppression of TGF-β1-mediated Smad2/3 signalling in vivo and in vitro.

CONCLUSION

Strategies for enhancing BMP4 signalling may represent an effective treatment for pulmonary fibrosis.

Cathelicidin Treatment Silences Epithelial-Mesenchymal Transition Involved in Pulmonary Fibrosis in a Murine Model of Hypersensitivity Pneumonitis

Pulmonary fibrosis is becoming an increasingly common pathology worldwide. Unfortunately, this disorder is characterized by a bad prognosis: no treatment is known, and the survival rate is dramatically low. One of the most frequent reasons for pulmonary fibrosis is hypersensitivity pneumonitis (HP). As the main mechanism of pulmonary fibrosis is a pathology of the repair of wounded pulmonary epithelium with a pivotal role in epithelial-mesenchymal transition (EMT), we assumed that EMT silencing could prevent disease development. Because of several biological features including wound healing promotion, an ideal candidate for use in the treatment of pulmonary fibrosis seems to be cathelicidin. The aim of the studies was to understand the influence of cathelicidin on the EMT process occurring during lung fibrosis development in the course of HP. Cathelicidin's impact on EMT was examined in a murine model of HP, wherein lung fibrosis was induced by chronic exposure to extract of Pantoea agglomerans (SE-PA) by real-time PCR and Western blotting. Studies revealed that mouse exposure to cathelicidin did not cause any side changes in the expression of investigated genes/proteins. Simultaneously, cathelicidin administered together or after SE-PA decreased the elevated level of myofibroblast markers (Acta2/α-smooth muscle actin, Cdh2/N-cadherin, Fn1/Fibronectin, Vim/vimentin) and increased the lowered level of epithelial markers (Cdh1/E-cadherin, Ocln/occludin). Cathelicidin provided with SE-PA or after cessation of SE-PA inhalations reduced the expression of EMT-associated factors (Ctnnd1/β-catenin, Nfkb1/NFκB, Snail1/Snail, Tgfb1/TGFβ1 Zeb1/ZEB1, Zeb2/ZEB2) elevated by P. agglomerans. Cathelicidin's beneficial impact on the expression of genes/proteins involved in EMT was observed during and after the HP development; however, cathelicidin was not able to completely neutralize the negative changes. Nevertheless, significant EMT silencing in response to cathelicidin suggested the possibility of its use in the prevention/treatment of pulmonary fibrosis.

Gut microbiome and metabolites: The potential key roles in pulmonary fibrosis

There are a wide variety of microbiomes in the human body, most of which exist in the gastrointestinal tract. Microbiomes and metabolites interact with the host to influence health. Rapid progress has been made in the study of its relationship with abenteric organs, especially lung diseases, and the concept the of "gut-lung axis" has emerged. In recent years, with the in-depth study of the "gut-lung axis," it has been found that changes of the gut microbiome and metabolites are related to fibrotic interstitial lung disease. Understanding their effects on pulmonary fibrosis is expected to provide new possibilities for the prevention, diagnosis and even treatment of pulmonary fibrosis. In this review, we focused on fibrotic interstitial lung disease, summarized the changes the gut microbiome and several metabolites of the gut microbiome in different types of pulmonary fibrosis, and discussed their contributions to the occurrence and development of pulmonary fibrosis.

Destructive fibrotic teamwork: how both microenvironment stiffness and profibrotic interleukin 13 impair alveolar macrophage phenotype and function

The pulmonary fibrotic microenvironment is characterized by increased stiffness of lung tissue and enhanced secretion of profibrotic soluble cues contributing to a feedback loop that leads to dysregulated wound healing and lung failure. Pinpointing the individual and tandem effects of profibrotic stimuli in impairing immune cell response remains difficult and is needed for improved therapeutic strategies. We utilized a statistical design of experiment (DOE) to investigate how microenvironment stiffness and interleukin 13 (IL13), a profibrotic soluble factor linked with disease severity, contribute to the impaired macrophage response commonly observed in pulmonary fibrosis. We used engineered bioinspired hydrogels of different stiffness, ranging from healthy to fibrotic lung tissue, and cultured murine alveolar macrophages (MH-S cells) with or without IL13 to quantify cell response and analyze independent and synergistic effects. We found that, while both stiffness and IL13 independently influence macrophage morphology, phenotype, phagocytosis and efferocytosis, these factors work synergistically to exacerbate impaired macrophage phenotype and efferocytosis. These unique findings provide insights into how macrophages in fibrotic conditions are not as effective in clearing debris, contributing to fibrosis initiation/progression, and more broadly inform how underlying drivers of fibrosis modulate immune cell response to facilitate therapeutic strategies.

Exosomes derived from hypoxia-induced alveolar epithelial cells stimulate interstitial pulmonary fibrosis through a HOTAIRM1-dependent mechanism

Pulmonary fibrosis is the result of various diseases with no satisfactory treatment approaches. The exosome-mediated transfer of long noncoding RNAs (lncRNAs) has been implicated in the pathological process of lung diseases. Herein, we investigated the therapeutic potential of HOTAIRM1 transferred by alveolar epithelial cell (AEC)-derived exosomes in interstitial pulmonary fibrosis (IPF) and the potential molecular mechanisms. Next-generation sequencing-based gene expression profiling was employed to identify lncRNAs related to IPF. Exosomes were isolated from hypoxia-induced AECs (AEC-exosomes) and identified before use. HOTAIRM1 expression was examined in bleomycin-induced IPF mouse models and the isolated exosomes, and the miRNA downstream of HOTAIRM1 was analyzed. HOTAIRM1 expression was increased in the lung tissues of IPF mice and AEC exosomes. HOTAIRM1 delivered by AEC-exosomes promoted the proliferation and transdifferentiation of lung fibroblasts (LFs). Mechanistically, HOTAIRM1 competitively bound to miR-30d-3p and recruited YY1 to upregulate HSF1 expression. In addition, miR-30d-3p targeted HSF1 by binding to its 3'-UTR and reduced its expression. In vivo assays confirmed the promoting effect of exosomes-HOTAIRM1 on extracellular matrix remodeling by regulating the miR-30d-3p/HSF1/YY1 axis. Overall, HOTAIRM1 loaded by AEC exosomes can accelerate IPF by disrupting miR-30d-3p-mediated inhibition of HSF1 and inducing recruitment of HSF1 by YY1. These results highlight a promising strategy to overcome IPF.

DR7dA, a Novel Antioxidant Peptide Analog, Demonstrates Antifibrotic Activity in Pulmonary Fibrosis In Vivo and In Vitro

Pulmonary fibrosis (PF), which is characterized by enhanced extracellular matrix (ECM) deposition, is an interstitial lung disease that lacks an ideal clinical treatment strategy. It has an extremely poor prognosis, with an average survival of 3-5 years after diagnosis. Our previous studies have shown that the antioxidant peptide DR8 (DHNNPQIR-NH2), which is extracted and purified from rapeseed, can alleviate PF and renal fibrosis. However, natural peptides are easily degraded by proteases in vivo, which limits their potency. We have since synthesized a series of DR8 analogs based on amino acid scanning substitution. DR7dA [DHNNPQ (D-alanine) R-NH2] is an analog of DR8 in which L-isoleucine (L-Ile) is replaced with D-alanine (D-Ala), and its half-life is better than that of DR8. In the current study, we verified that DR7dA ameliorated tumor growth factor (TGF)-β1-induced fibrogenesis and bleomycin-induced PF. The results indicated that DR7dA reduced the protein and mRNA levels of TGF-β1 target genes in TGF-β1-induced models. Surprisingly, DR7dA blocked fibrosis in a lower concentration range than DR8 in cells. In addition, DR7dA ameliorated tissue pathologic changes and ECM accumulation in mice. BLM caused severe oxidative damage, but administration of DR7dA reduced oxidative stress and restored antioxidant defense. Mechanistic studies suggested that DR7dA inhibits ERK, P38, and JNK phosphorylation in vivo and in vitro All results indicated that DR7dA attenuated PF by inhibiting ECM deposition and oxidative stress via blockade of the mitogen-activated protein kinase (MAPK) pathway. Hence, compared with its parent peptide, DR7dA has higher druggability and could be a candidate compound for PF treatment in the future. SIGNIFICANCE STATEMENT: In order to improve druggability of DR8, we investigated the structure-activity relationship of it and replaced the L-isoleucine with D-alanine. We found that the stability and antifibrotic activity of DR7dA were significantly improved than DR8, as well as DR7dA significantly attenuated tumor growth factor (TGF)-β1-induced fibrogenesis and ameliorated bleomycin-induced fibrosis by inhibiting extracellular matrix deposition and oxidative stress via blockade of the MAPK pathway, suggesting DR7dA may be a promising candidate compound for the treatment of PF.

Effects of bone morphogenetic protein 4 on TGF-β1-induced cell proliferation, apoptosis, activation and differentiation in mouse lung fibroblasts via ERK/p38 MAPK signaling pathway

Fibroblasts, in particular myofibroblasts, are the critical effector cells in idiopathic pulmonary fibrosis (IPF), a deadly lung disease characterized by abnormal lung remodeling and the formation of "fibroblastic foci". Aberrant activation of TGF-β1 is frequently encountered and promotes fibroblast proliferation, activation, and differentiation in pulmonary fibrosis. Hence, the inhibition of TGF-β1-induced lung fibroblast activation holds promise as a therapeutic strategy for IPF. The present study aimed to investigate the potential effect and underlying mechanisms of bone morphogenetic protein 4 (BMP4) on TGF-β1-induced proliferation, apoptosis, activation and myofibroblast differentiation of adult lung fibroblasts. Here, we demonstrated that BMP4 expression was significantly decreased in TGF-β1-stimulated mouse primary lung fibroblasts (PLFs). BMP4 inhibited proliferation and apoptosis resistance of TGF-β1-stimulated mouse PLFs. BMP4 suppressed TGF-β1-induced fibroblast activation and differentiation in mouse PLFs. We also found that BMP4 inhibited TGF-β1-induced ERK and p38 MAPK phosphorylation. Our findings indicate that BMP4 exerts its anti-fibrotic effects by regulating fibroblast proliferation, apoptosis, activation and differentiation via the inhibition of the ERK/p38 MAPK signaling pathway, and thus has a potential for the treatment of pulmonary fibrosis.

Insights into the Pathogenesis of Pulmonary Fibrosis from Genetic Diseases

Pulmonary fibrosis is a disease process associated with significant morbidity and mortality, with limited therapeutic options owing to an incomplete understanding of the underlying pathophysiology. Mechanisms driving the fibrotic cascade have been elucidated through studies of rare and common variants in surfactant-related and telomere-related genes in familial and sporadic forms of pulmonary fibrosis, as well as in multisystem Mendelian genetic disorders that present with pulmonary fibrosis. In this translational review, we outline insights into the pathophysiology of pulmonary fibrosis derived from genetic forms of the disease, with a focus on model systems, shared cellular and molecular mechanisms, and potential targets for therapy.