Alveolar epithelial cell-derived Sonic hedgehog promotes pulmonary fibrosis through OPN-dependent alternative macrophage activation

The role of macrophage polarization and cellular crosstalk in the pulmonary fibrotic microenvironment: a review

Pulmonary fibrosis (PF) is a progressive interstitial inflammatory disease with a high mortality rate. Patients with PF commonly experience a chronic dry cough and progressive dyspnoea for years without effective mitigation. The pathogenesis of PF is believed to be associated with dysfunctional macrophage polarization, fibroblast proliferation, and the loss of epithelial cells. Thus, it is of great importance and necessity to explore the interactions among macrophages, fibroblasts, and alveolar epithelial cells in lung fibrosis, as well as in the pro-fibrotic microenvironment. In this review, we discuss the latest studies that have investigated macrophage polarization and activation of non-immune cells in the context of PF pathogenesis and progression. Next, we discuss how profibrotic cellular crosstalk is promoted in the PF microenvironment by multiple cytokines, chemokines, and signalling pathways. And finally, we discuss the potential mechanisms of fibrogenesis development and efficient therapeutic strategies for the disease. Herein, we provide a comprehensive summary of the vital role of macrophage polarization in PF and its profibrotic crosstalk with fibroblasts and alveolar epithelial cells and suggest potential treatment strategies to target their cellular communication in the microenvironment.

M2a macrophages regulate fibrosis and affect the outcome after stroke via PU.1/mTOR pathway in fibroblasts

The moderate formation of the fibrotic scar plays an important role in functional recovery after stroke. M2a macrophages have been identified as an important source of early fibrosis after cerebral ischemia. However, the underlying mechanisms by which macrophages interact with fibroblasts in this context remain largely unknown. Therefore, our study aimed to further investigate the potential mechanisms underlying the effects of macrophages on fibroblasts following ischemic stroke. In vitro and in vivo, recombinant rat interleukin 4 (IL4) was used to induce macrophages to polarize into M2a macrophages. In vitro, primary Sprague-Dawley newborn rat meningeal-derived fibroblasts were treated with PU.1 knockdown, the PU.1 inhibitor DB1976 or the mTOR inhibitor rapamycin, which were then co-cultured with M2a macrophage conditioned medium (MCM). In vivo, Sprague-Dawley adult rats were infected with negative control adenoviruses or PU.1-shRNA adenoviruses. Ten days after infection, an injury model of middle cerebral artery occlusion/reperfusion (MCAO/R) was constructed. Subsequently, IL4 was injected intracerebroventricularly to induce M2a macrophages polarization. In vitro, M2a MCM upregulated PU.1 expression and promoted the differentiation, proliferation, migration and extracellular matrix generation of fibroblasts, which could be reversed by treatment with the PU.1 inhibitor DB1976 or PU.1 knockdown. In vivo, PU.1 expression in fibroblasts was increased within ischemic core following MCAO/R, and this upregulation was further enhanced by exposure to IL4. Treatment with IL4 promoted fibrosis, increased angiogenesis, reduced apoptosis and infarct volume, as well as mitigated neurological deficits after MCAO/R, and these effects could be reversed by PU.1 knockdown. Furthermore, both in vivo and in vitro studies showed that IL4 treatment increased the levels of phosphorylated Akt and mTOR proteins, which were markedly decreased by PU.1 knockdown. Additionally, the use of an mTOR inhibitor rapamycin obviously suppressed the migration and differentiation of fibroblasts, and Col1 synthesis. In conclusion, our findings suggest for the first time that M2a macrophages, at least in part, regulate fibrosis and affect the outcome after cerebral ischemic stroke via the PU.1/mTOR signaling pathway in fibroblasts.

Biomass-related PM2.5 induced inflammatory microenvironment via IL-17F/IL-17RC axis

Biomass exposure is a significant environmental risk factor for COPD, but the underlying mechanisms have not yet been fully elucidated. Inflammatory microenvironment has been shown to drive the development of many chronic diseases. Pollution exposure can cause increased levels of inflammatory factors in the lungs, leading to an inflammatory microenvironment which is prevalent in COPD. Our findings revealed that IL-17F was elevated in COPD, while exposure to biomass led to increased expression of IL-17F in both alveolar epithelial and macrophage cells in mice. Blocking IL-17F could alleviate the lung inflammation induced by seven days of biomass exposure in mice. We employed a transwell co-culture system to simulate the microenvironment and investigate the interactions between MLE-12 and MH-S cells. We demonstrated that anti-IL-17F antibody attenuated the inflammatory responses induced by BRPM2.5 in MLE-12 and MH-S co-cultured with BRPM2.5-MLE-12, which reduced inflammatory changes in microenvironment. We found that IL-17RC, an important receptor for IL-17F, played a key role in the interactions. Knockout of IL-17RC in MH-S resulted in inhibited IL-17F signaling and attenuated inflammatory response after MH-S co-culture with BRPM2.5-MLE-12. Our investigation suggests that BRPM2.5 induces lung epithelial-macrophage interactions via IL-17F/IL-17RC axis regulating the inflammatory response. These results may provide a novel strategy for effective prevention and treatment of biomass-related COPD.

Osteopontin: an essential regulatory protein in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive, chronic lung disease characterized by abnormal proliferation and activation of fibroblasts, excessive accumulation of extracellular matrix (ECM), inflammatory damage, and disrupted alveolar structure. Despite its increasing morbidity and mortality rates, effective clinical treatments for IPF remain elusive. Osteopontin (OPN), a multifunctional ECM protein found in various tissues, has been implicated in numerous biological processes such as bone remodeling, innate immunity, acute and chronic inflammation, and cancer. Recent studies have highlighted the pivotal role of OPN in the pathogenesis of IPF. This review aims to delve into the involvement of OPN in the inflammatory response, ECM deposition, and epithelial-mesenchymal transition (EMT) during IPF, and intends to lay a solid theoretical groundwork for the development of therapeutic strategies for IPF.

Osteopontin: A Novel Therapeutic Target for Respiratory Diseases

Osteopontin (OPN) is a multifunctional phosphorylated protein that is involved in physiological and pathological events. Emerging evidence suggests that OPN also plays a critical role in the pathogenesis of respiratory diseases. OPN can be produced and secreted by various cell types in lungs and overexpression of OPN has been found in acute lung injury/acute respiratory distress syndrome (ALI/ARDS), pulmonary hypertension (PH), pulmonary fibrosis diseases, lung cancer, lung infection, chronic obstructive pulmonary disease (COPD), and asthma. OPN exerts diverse effects on the inflammatory response, immune cell activation, fibrosis and tissue remodeling, and tumorigenesis of these respiratory diseases, and genetic and pharmacological moudulation of OPN exerts therapeutic effects in the treatment of respiratory diseases. In this review, we summarize the recent evidence of multifaceted roles and underlying mechanisms of OPN in these respiratory diseases, and targeting OPN appears to be a potential therapeutic intervention for these diseases.

Spatial targeting of fibrosis-promoting macrophages with nanoscale metal-organic frameworks for idiopathic pulmonary fibrosis therapy

Targeted delivery of therapeutic drugs to fibrosis-promoting macrophages (FPMs) holds promise as a challenging yet effective approach for the treatment of idiopathic pulmonary fibrosis (IPF). Here, nanocarriers composed of Mn-curcumin metal-organic frameworks (MOFs) were utilized to deliver the immune inhibitor BLZ-945 to the lungs, with the goal of depleting fibrosis-promoting macrophages (FPMs) from fibrotic lung tissues. FPM targeting was achieved by functionalizing the nanocarrier surface with an M2-like FPM binding peptide (M2pep). As a result, significant therapeutic benefits were observed through the successful depletion of approximately 80 % of the M2-like macrophages (FPMs) in a bleomycin-induced fibrosis mouse model treated with the designed M2-like FPM-targeting nanoparticle (referred to as M2NP-BLZ@Mn-Cur). Importantly, the released Mn2+ and curcumin after the degradation of M2NP-BLZ@Mn-Cur accumulated in the fibrotic lung tissue, which can alleviate inflammation and oxidative stress reactions, thereby further improving IPF therapy. This study presents a novel strategy with promising prospects for molecular-targeted fibrosis therapy. STATEMENT OF SIGNIFICANCE: Metal-organic frameworks (MOFs)- based nanocarriers equipped with both fibrosis-promoting macrophage (FPM)-specific targeting ability and therapeutic drugs are appealing for pulmonary fibrosis treatment. Here, we prepared M2pep (an M2-like FPM binding peptide)-modified and BLZ945 (a small molecule inhibitor of CSF1/CSF-1R axis)-loaded Mn-curcumin MOF nanoparticles (M2NP-BLZ@Mn-Cur) for pulmonary fibrosis therapy. The functionalized M2NP-BLZ@Mn-Cur nanoparticles can be preferentially taken up by FPMs, resulting in their depletion from fibrotic lung tissues. In addition, Mn2+and curcumin released from the nanocarriers have anti-inflammation and immune regulation effects, which further enhance the antifibrotic effect of the nanoparticles.

The critical role of osteopontin (OPN) in fibrotic diseases

Fibrosis is a pathological condition characterized by the excessive deposition of extracellular matrix components in tissues and organs, leading to progressive architectural remodelling and contributing to the development of various diseases. Osteopontin (OPN), a highly phosphorylated glycoprotein, has been increasingly recognized for its involvement in the progression of tissue fibrosis. This review provides a comprehensive overview of the genetic and protein structure of OPN and focuses on our current understanding of the role of OPN in the development of fibrosis in the lungs and other tissues. Additionally, special attention is given to the potential of OPN as a biomarker and a novel therapeutic target in the treatment of fibrosis.

Increased expression of OPN contributes to idiopathic pulmonary fibrosis and indicates a poor prognosis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is fibrotic lung disease with no effective treatment. It is characterized by destruction of alveolar structure and pulmonary interstitial fibrosis, leading to dyspnea and even asphyxia death of patients. Epithelial-mesenchymal transition (EMT) is considered to be a driving factor in the pathogenesis of IPF. Osteopontin (OPN) is a secreted protein widely present in the extracellular matrix and involved in the occurrence and development of a variety of diseases.

METHODS

The original datasets were obtained from NCBI GEO databases analyzed with the online tool GEO2R and EasyGEO. Bleomycin induced mouse pulmonary fibrosis model and OPN/OPN-biotin treated mouse model were established to investigate the role of OPN in mouse pulmonary fibrosis and the target cells of OPN. A549 cells and HBE cells were used to explore the mechanism of OPN-induced epithelial-mesenchymal transition (EMT) in epithelial cells and mass spectrometry was used to detect OPN downstream receptors. Precision-cut lung slices and lentivirus-treated mice with pulmonary fibrosis were used to examine the therapeutic effect of OPN and its downstream pathways on pulmonary fibrosis.

RESULTS

We demonstrate that the content of OPN in IPF bronchoalveolar lavage fluid (BALF) is high compared to the normal groups, and its expression level is correlated with prognosis. At the animal level, OPN was highly expressed at all stages of pulmonary fibrosis in mice, and the bronchoalveolar lavage fluid (BALF) could accurately reflect its expression in the lung. Next, we reveal that OPN was mainly expressed by macrophages and the main target cells of OPN were epithelial cells. Mice developed pulmonary fibrosis accompanied after treating the mice with OPN. Both in vitro and in vivo experiments confirmed that OPN could induce EMT of alveolar epithelial cells. Mechanistically, OPN binding triggered phosphorylation of FAK by CD44, thus activating snail1-mediated profibrotic protein synthesis. Inhibition of FAK phosphorylation and its downstream pathways can effectively alleviate pulmonary fibrosis in precision sections of lung tissue (PCLS) assay. OPN knockdown in bleomycin-induced lung fibrosis mice led to significantly less fibrosis.

CONCLUSION

Our data suggest that OPN mediates lung fibrosis through EMT, implicating its potential therapeutic target and prognostic indicator role for IPF. OPN may be a target for the diagnosis and treatment of IPF.

Sonic Hedgehog Signaling Is Essential for Pulmonary Ionocyte Specification in Human and Ferret Airway Epithelia

Pulmonary ionocytes express high levels of cystic fibrosis transmembrane conductance regulator (CFTR), an anion channel that is critical for hydration of the airways and mucociliary clearance. However, the cellular mechanisms that govern ionocyte specification and function remain unclear. We observed that increased abundance of ionocytes in cystic fibrosis (CF) airway epithelium was associated with enhanced expression of Sonic Hedgehog (SHH) effectors. In this study, we evaluated whether the SHH pathway directly impacts ionocyte differentiation and CFTR function in airway epithelia. Pharmacological HPI1-mediated inhibition of SHH signaling component GLI1 significantly impaired human basal cell specification of ionocytes and ciliated cells but significantly enhanced specification of secretory cells. By contrast, activation of the SHH pathway effector smoothened (SMO) with the chemical agonist SAG significantly enhanced ionocyte specification. The abundance of CFTR+ BSND+ ionocytes under these conditions had a direct relationship with CFTR-mediated currents in differentiated air-liquid interface (ALI) airway cultures. These findings were corroborated in ferret ALI airway cultures generated from basal cells in which the genes encoding the SHH receptor PTCH1 or its intracellular effector SMO were genetically ablated using CRISPR-Cas9, causing aberrant activation or suppression of SHH signaling, respectively. These findings demonstrate that SHH signaling is directly involved in airway basal cell specification of CFTR-expressing pulmonary ionocytes and is likely responsible for enhanced ionocyte abundance in the CF proximal airways. Pharmacologic approaches to enhance ionocyte and reduce secretory cell specification after CFTR gene editing of basal cells may have utility in the treatment of CF.

Molecular mechanisms of COVID-19-induced pulmonary fibrosis and epithelial-mesenchymal transition

As the outbreak of COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) first broke out in Hubei Province, China, at the end of 2019. It has brought great challenges and harms to global public health. SARS-CoV-2 mainly affects the lungs and is mainly manifested as pulmonary disease. However, one of the biggest crises arises from the emergence of COVID-19-induced fibrosis. At present, there are still many questions about how COVID-19 induced pulmonary fibrosis (PF) occurs and how to treat and regulate its long-term effects. In addition, as an important process of fibrosis, the effect of COVID-19 on epithelial-mesenchymal transition (EMT) may be an important factor driving PF. This review summarizes the main pathogenesis and treatment mechanisms of COVID-19 related to PF. Starting with the basic mechanisms of PF, such as EMT, transforming growth factor-β (TGF-β), fibroblasts and myofibroblasts, inflammation, macrophages, innate lymphoid cells, matrix metalloproteinases and tissue inhibitors of metalloproteinases, hedgehog pathway as well as Notch signaling. Further, we highlight the importance of COVID-19-induced EMT in the process of PF and provide an overview of the related molecular mechanisms, which will facilitate future research to propose new clinical therapeutic solutions for the treatment of COVID-19-induced PF.

Cuproptosis-related gene CDKN2A as a molecular target for IPF diagnosis and therapeutics

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a progressive chronic interstitial lung disease with limited therapeutic options. Cuproptosis is a recently proposed novel form of programmed cell death, which has been strongly implicated in the development of various human diseases. However, the prognostic and therapeutic value of cuproptosis-related genes (CRGs) in IPF remains to be elucidated.

METHODS

In the present study, weighted gene co-expression network analysis (WGCNA) was employed to identify the key CRGs associated with the development of IPF. The subsequent GSEA, immune cell correlation analysis, and single-cell RNA-Seq analysis were conducted to explore the potential role of the identified CRGs in IPF. In addition, ROC curves and survival analysis were used to assess the prognostic value of the key CRGs in IPF. Moreover, we explored the molecular mechanisms of participation of identified key CRGs in the development of pulmonary fibrogenesis through in vivo and in vitro experiments.

RESULTS

The expression level of cyclin-dependent kinase inhibitor 2A (CDKN2A) is upregulated in the lung tissues of IPF patients and associated with disease severity. Notably, CDKN2A was constitutively expressed by fibrosis-promoting M2 macrophages. Decreased CDKN2A expression sensitizes M2 macrophages to elesclomol-induced cuproptosis in vitro. Inhibition of CDKN2A decreases the number of viable macrophages and attenuates bleomycin-induced pulmonary fibrosis in mice.

CONCLUSION

These findings indicate that CDKN2A mediates the resistance of fibrosis-promoting M2 macrophages to cuproptosis and promotes pulmonary fibrosis in mice. Our work provides fresh insights into CRGs in IPF with potential value for research in the pathogenesis, diagnosis, and a new therapy strategy for IPF.

Regulatory T cells promote functional recovery after spinal cord injury by alleviating microglia inflammation via STAT3 inhibition

BACKGROUND

Immediately after spinal trauma, immune cells, and proinflammatory cytokines infiltrate the spinal cord and disrupt the focal microenvironment, which impedes axon regeneration and functional recovery. Previous studies have reported that regulatory T cells (Tregs) enter the central nervous system and exert immunosuppressive effects on microglia during multiple sclerosis and stroke. However, whether and how Tregs interact with microglia and modulate injured microenvironments after spinal cord injury (SCI) remains unknown.

METHOD

Regulatory T cells spatiotemporal characteristics were analyzed in a mouse contusion SCI model. Microglia activation status was evaluated by immunostaining and RNA sequencing. Cytokine production in injured spinal cord was examined using Luminex. The role of STAT3 in Treg-microglia crosstalk was investigated in a transwell system with isolated Tregs and primary microglia.

RESULTS

Regulatory T cells infiltration of the spinal cord peaked on day 7 after SCI. Treg depletion promoted microglia switch to a proinflammatory phenotype. Inflammation-related genes, such as ApoD, as well as downstream cytokines IL-6 and TNF-α were upregulated in microglia in Treg-depleted mice. STAT3 inhibition was involved in Treg-microglia crosstalk, and STAT3 chemical blockade improved function recovery in Treg-depleted mice.

CONCLUSION

Our results suggest that Tregs promote functional recovery after SCI by alleviating microglia inflammatory reaction via STAT3.

Total flavonoid extract from Dracocephalum moldavica L. improves pulmonary fibrosis by reducing inflammation and inhibiting the hedgehog signaling pathway

Dracocephalum Moldavica L. is a traditional herb for improving pharynx and relieving cough. However, the effect on pulmonary fibrosis is not clear. In this study, we explored the impact and molecular mechanism of total flavonoid extract from Dracocephalum moldavica L. (TFDM) on bleomycin-induced pulmonary fibrosis mouse model. Lung function testing, lung inflammation and fibrosis, and the related factors were detected by the lung function analysis system, HE and Masson staining, ELISA, respectively. The expression of proteins was studied through Western Blot, immunohistochemistry, and immunofluorescence while the expression of genes was analyzed by RT-PCR. The results showed that TFDM significantly improved lung function in mice, reduced the content of inflammatory factors, thereby reducing the inflammation. It was found that expression of collagen type I, fibronectin, and α-smooth muscle actin was significantly decreased by TFDM. The results further showed that TFDM interferes with hedgehog signaling pathway by decreasing the expression of Shh, Ptch1, and SMO proteins and thereby inhibiting the generation of downstream target gene Gli1 and thus improving pulmonary fibrosis. Conclusively, these findings suggest that TFDM improve pulmonary fibrosis by reducing inflammation and inhibition of the hedgehog signaling pathway.

Advances in the role of STAT3 in macrophage polarization

The physiological processes of cell growth, proliferation, differentiation, and apoptosis are closely related to STAT3, and it has been demonstrated that aberrant STAT3 expression has an impact on the onset and progression of a number of inflammatory immunological disorders, fibrotic diseases, and malignancies. In order to produce the necessary biological effects, macrophages (M0) can be polarized into pro-inflammatory (M1) and anti-inflammatory (M2) types in response to various microenvironmental stimuli. STAT3 signaling is involved in macrophage polarization, and the research of the effect of STAT3 on macrophage polarization has gained attention in recent years. In order to provide references for the treatment and investigation of disorders related to macrophage polarization, this review compiles the pertinent signaling pathways associated with STAT3 and macrophage polarization from many fundamental studies.

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

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

Alveolar Epithelial Type 2 Cell Dysfunction in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and irreversible pulmonary interstitial disease that seriously affects the patient's quality of life and lifespan. The pathogenesis of IPF has not been clarified, and its treatment is limited to pirfenidone and nintedanib, which only delays the decline of lung function. Alveolar epithelial type 2 (AT2) cells are indispensable in the regeneration and lung surfactant secretion of alveolar epithelial cells. Studies have shown that AT2 cell dysfunction initiates the occurrence and progression of IPF. This review expounds on the AT2 cell dysfunction in IPF, involving senescence, apoptosis, endoplasmic reticulum stress, mitochondrial damage, metabolic reprogramming, and the transitional state of AT2 cells. This article also briefly summarizes potential treatments targeting AT2 cell dysfunction.

The Role of Osteopontin in Tumor Progression Through Tumor-Associated Macrophages

Osteopontin (OPN) is a multifunctional phosphorylated protein. It is widely involved in solid tumor progression, such as intensification of macrophage recruitment, inhibition of T-cell activity, aggravation of tumor interstitial fibrosis, promotion of tumor metastasis, chemotherapy resistance, and angiogenesis. Most of these pathologies are affected by tumor-associated macrophages (TAMs), an important component of the tumor microenvironment (TME). TAMs have been extensively characterized, including their subsets, phenotypes, activation status, and functions, and are considered a promising therapeutic target for cancer treatment. This review focuses on the interaction between OPN and TAMs in mediating tumor progression. We discuss the strategies for targeting OPN and TAMs to treat cancer and factors that may affect the therapeutic outcomes of blocking OPN or depleting TAMs. We also discuss the role of cancer cell- vs. TAM-derived OPN in tumorigenesis, the mechanisms of how OPN affects TAM recruitment and polarization, and why OPN could mediate anti-tumor and pro-tumor effects, as well as previously reported discrepancies.

Dichotomous Roles of Men1 in Macrophages and Fibroblasts in Bleomycin-Induced Pulmonary Fibrosis

Pulmonary fibrosis therapy is limited by the unclear mechanism of its pathogenesis. C57BL/6 mice were used to construct the pulmonary fibrosis model in this study. The results showed that Men1, which encodes menin protein, was significantly downregulated in bleomycin (BLM)—induced pulmonary fibrosis. Mice were made to overexpress or had Men1 knockdown with adeno-associated virus (AAV) infection and then induced with pulmonary fibrosis. BLM—induced pulmonary fibrosis was attenuated by Men1 overexpression and exacerbated by Men1 knockdown. Further analysis revealed the distinct roles of Men1 in fibroblasts and macrophages. Men1 inhibited fibroblast activation and extracellular matrix (ECM) protein expression while promoting macrophages to be profibrotic (M2) phenotype and enhancing their migration. Accordingly, pyroptosis was potentiated by Men1 in mouse peritoneal macrophages (PMCs) and lung tissues upon BLM stimulation. Furthermore, the expression of profibrotic factor OPN was positively regulated by menin in Raw264.7 cells and lung tissues by binding to the OPN promoter region. Taken together, although Men1 showed antifibrotic properties in BLM—induced pulmonary fibrosis mice, conflictive roles of Men1 were displayed in fibroblasts and macrophages. The profibrotic role of Men1 in macrophages may occur via the regulation of macrophage pyroptosis and OPN expression. This study extends the current pathogenic understanding of pulmonary fibrosis.

C/EBP homologous protein promotes Sonic Hedgehog secretion from type II alveolar epithelial cells and activates Hedgehog signaling pathway of fibroblast in pulmonary fibrosis

Background

Endoplasmic reticulum (ER) stress is involved in the pathological process of pulmonary fibrosis, including IPF. It affects a broad scope of cellular types during pulmonary fibrosis but the role in epithelial-mesenchymal crosstalk has not been fully defined. The present study aimed to investigate the effects of Shh secretion by ER  stress-challenged type II alveolar epithelial cells (AECII) on fibroblast and pulmonary fibrosis.

Methods

Conditioned medium (CM) from tunicamycin (TM)-treated AECII was collected and incubated with fibroblast. Short hairpin RNA (shRNA) was used for RNA interference of C/EBP homologous protein (CHOP). The effects of CHOP and HH signaling were evaluated by TM administration under the background of bleomycin-induced pulmonary fibrosis in mice.

Results

Both expression of CHOP and Shh in AECII, and HH signaling in mesenchyme were upregulated in IPF lung. TM-induced Shh secretion from AECII activates HH signaling and promotes pro-fibrotic effects of fibroblast. Interfering CHOP expression reduced ER stress-induced Shh secretion and alleviated pulmonary fibrosis in mice.

Conclusions

Our work identified a novel mechanism by which ER stress is involved in pulmonary fibrosis. Inhibition of ER stress or CHOP in epithelial cells alleviated pulmonary fibrosis by suppressing Shh/HH signaling pathway of fibroblasts.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02012-x.

Cell-to-Cell Crosstalk: A New Insight into Pulmonary Hypertension

Pulmonary hypertension (PH) is a disease with high pulmonary arterial pressure, pulmonary vasoconstriction, pulmonary vascular remodeling, and microthrombosis in complex plexiform lesions, but it has been unclear of the exact mechanism of PH. A new understanding of the pathogenesis of PH is occurred and focused on the role of crosstalk between the cells on pulmonary vessels and pulmonary alveoli. It was found that the crosstalks among the endothelial cells, smooth muscle cells, fibroblasts, pericytes, alveolar epithelial cells, and macrophages play important roles in cell proliferation, migration, inflammation, and so on. Therefore, the heterogeneity of multiple pulmonary blood vessels and alveolar cells and tracking the transmitters of cell communication could be conducive to the further insights into the pathogenesis of PH to discover the potential therapeutic targets for PH.

A Noncanonical Hedgehog Signaling Exerts a Tumor-Promoting Effect on Pancreatic Cancer Cells Via Induction of Osteopontin Expression

Objective: Sonic Hedgehog (Shh)-Gli1 signaling and osteopontin (OPN) play vital roles in pancreatic cancer. However, the precise mechanisms of both signals have not been fully clarified, and whether there is a correlation between them in pancreatic ductal adenocarcinoma (PDAC) is unknown. This study aims to confirm the effect of OPN on human PDAC and assess whether Hh signaling affects pancreatic cancer cells through upregulation of OPN. Materials and Methods: OPN expression in human PDAC tissues and cell lines was investigated. Proliferation, apoptosis, migration, and invasion of OPN-knockdown BxPC-3 cells were observed. We analyzed the correlation between Shh or Gli1 and OPN expression in human PDAC. Hh signaling inhibitors and shRNA against Gli1 were used to confirm if OPN expression in BxPC-3 cells was regulated by Hh canonical or noncanonical pathway. We also evaluated the proliferation, apoptosis, migration, and invasion of Gli1-knockdown BxPC-3 cells. Results: OPN is highly expressed in human PDAC tissues and cell lines. The proliferation, migration, and invasion of BxPC-3 cell lines were decreased, whereas apoptosis was increased when OPN was knocked down. Correlation analysis showed that Gli1, but not Shh, was associated with OPN expression in human PDAC, and Gli1 regulated OPN production in BxPC-3 cells through a noncanonical pathway because Gli but not Smo inhibitor reduced OPN expression. Similar to above, the proliferation, migration, and invasion of BxPC-3 cells were decreased, whereas the apoptosis was increased when Gli1 was knocked down. Supplement of exogenous OPN protein could partially reverse the effect of both OPN knockdown and Gli1 knockdown on the bio-behavior of BxPC-3 cells. Conclusion: Hh signaling promotes proliferation, migration, and invasion but inhibits apoptosis of pancreatic cancer cells through upregulation of OPN in a noncanonical pathway.

The Hedgehog Signaling Pathway in Idiopathic Pulmonary Fibrosis: Resurrection Time

The hedgehog (Hh) pathway is a sophisticated conserved cell signaling pathway that plays an essential role in controlling cell specification and proliferation, survival factors, and tissue patterning formation during embryonic development. Hh signal activity does not entirely disappear after development and may be reactivated in adulthood within tissue-injury-associated diseases, including idiopathic pulmonary fibrosis (IPF). The dysregulation of Hh-associated activating transcription factors, genomic abnormalities, and microenvironments is a co-factor that induces the initiation and progression of IPF.

Mesenchymal Stem Cell-Derived Exosomes Induced by IL-1β Attenuate Urethral Stricture Through Let-7c/PAK1/NF-κB-Regulated Macrophage M2 Polarization

Background

Urethral stricture is a clinical challenge for both patients and clinicians. Post-traumatic urethral stricture is associated with formation of scar tissue caused by excessive inflammation. The aim of this study is exploring potential therapeutic strategies for this condition.

Methods

In vivo experiments on New Zealand rabbits and in vitro experiments on THP-1 monocytes and urethral fibroblasts were performed to investigate the effects on post-traumatic urethral stricture of exosomes isolated from IL-1β-treated mesenchymal stem cells (Exo-MSCs^IL-1β) and the role of macrophage M2 polarization in this process. Additionally, related signaling and mechanism behind were explored.

Results

In a New Zealand rabbit model of post-traumatic urethral stricture, injection of Exo-MSCs^IL-1β significantly reduced urethral stricture and collagen fiber accumulation compared with Exo-MSCs. Addition of Exo-MSCs^IL-1β to THP-1 monocytes in vitro induced M2 macrophage polarization, which, in turn, inhibited activation of urethral fibroblasts and synthesis of collagen. Mechanistically, Exo-MSCs^IL-1β were found to contain high levels of the microRNA let-7c, and luciferase reporter assays showed that let-7c interacted with the 3'UTR of PAK1 mRNA. Transfection of THP-1 cells with a let-7c mimic downregulated PAK1 expression and inhibited activation of the NF-κB signaling pathway.

Conclusion

These results support a role for let-7c-containing Exo-MSCs^IL-1β in reducing urethral stricture via inhibition of PAK1-NF-κB signaling, M2 macrophage polarization, and differentiation of urethral myofibroblasts.

New Angiogenic Regulators Produced by TAMs: Perspective for Targeting Tumor Angiogenesis

Simple Summary

Since the targeting of a single pro-angiogenic factor fails to improve oncological disease outcome, significant efforts have been made to identify new pro-angiogenic factors that could compensate for the deficiency of current therapy or act independently as single drugs. Our review aims to present the state-of-the art for well-known and recently described factors produced by macrophages that induce and regulate angiogenesis. A number of positive and negative regulators of angiogenesis in the tumor microenvironment are produced by tumor-associated macrophages (TAMs). Accumulating evidence has indicated that, apart from the well-known angiogenic factors, there are plenty of novel angiogenesis-regulating proteins that belong to different classes. We summarize the data regarding the direct or indirect mechanisms of the interaction of these factors with endothelial cells during angiogenesis. We highlight the recent findings that explain the limitations in the efficiency of current anti-angiogenic therapy approaches.

Abstract

Angiogenesis is crucial to the supply of a growing tumor with nutrition and oxygen. Inhibition of angiogenesis is one of the main treatment strategies for colorectal, lung, breast, renal, and other solid cancers. However, currently applied drugs that target VEGF or receptor tyrosine kinases have limited efficiency, which raises a question concerning the mechanism of patient resistance to the already developed drugs. Tumor-associated macrophages (TAMs) were identified in the animal tumor models as a key inducer of the angiogenic switch. TAMs represent a potent source not only for VEGF, but also for a number of other pro-angiogenic factors. Our review provides information about the activity of secreted regulators of angiogenesis produced by TAMs. They include members of SEMA and S100A families, chitinase-like proteins, osteopontin, and SPARC. The COX-2, Tie2, and other factors that control the pro-angiogenic activity of TAMs are also discussed. We highlight how these recent findings explain the limitations in the efficiency of current anti-angiogenic therapy. Additionally, we describe genetic and posttranscriptional mechanisms that control the expression of factors regulating angiogenesis. Finally, we present prospects for the complex targeting of the pro-angiogenic activity of TAMs.

Metformin prevents PFKFB3-related aerobic glycolysis from enhancing collagen synthesis in lung fibroblasts by regulating AMPK/mTOR pathway

Aerobic glycolysis has been shown to contribute to the abnormal activation of lung fibroblasts with excessive collagen deposition in lipopolysaccharide (LPS)-induced pulmonary fibrosis. Targeting aerobic glycolysis in lung fibroblasts might therefore be considered as a promising therapeutic approach for LPS-induced pulmonary fibrosis. In the present study, the aim was to investigate whether metformin, a widely used agent for treating type 2 diabetes, could alleviate LPS-induced lung fibroblast collagen synthesis and its potential underlying mechanisms. Different concentrations of metformin were used to treat the human lung fibroblast MRC-5 cells after LPS challenge. Indicators of aerobic glycolysis in MRC-5 cells were detected by measuring glucose consumption and lactate levels in culture medium in addition to lactate dehydrogenase activity in cellular lysates. The glucose consumption, lactate levels and the lactate dehydrogenase activity were measured respectively using colorimetric/fluorometric and ELISA kits. The effects of metformin in AMP-activated protein kinase (AMPK) activation was assessed by mitochondrial complex I activity kits. Collagen I, α-smooth muscle actin (α-SMA) and collagen III were used as markers of collagen synthesis, which was measured using western blotting, whereas phosphorylated (p-) AMPK, AMPK, 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) and mTOR were detected by western blotting. Metformin significantly decreased mitochondrial complex I activity and upregulated the expression of p-AMPK/AMPK protein in a concentration-dependent manner. Furthermore, the aerobic glycolysis mediated by PFKFB3 and collagen synthesis in LPS-treated MRC-5 cells was gradually inhibited with increasing concentrations of metformin. However, this inhibitory role of metformin on PFKFB3-meditaed aerobic glycolysis and collagen synthesis was prevented by treatments with 3BDO and compound C, which are specific mTOR activator and AMPK inhibitor, respectively. Taken together, the findings from this study suggested that metformin may prevent PFKFB3-associated aerobic glycolysis from enhancing collagen synthesis in lung fibroblasts via regulating the AMPK/mTOR pathway.