Regulation of myofibroblast differentiation and bleomycin-induced pulmonary fibrosis by adrenomedullin

Gα12 and Gα13 proteins are required for transforming growth factor-β-induced myofibroblast differentiation

Myofibroblast differentiation, characterized by accumulation of cytoskeletal and extracellular matrix proteins by fibroblasts, is a key process in wound healing and pathogenesis of tissue fibrosis. Transforming growth factor-β (TGF-β) is the most powerful known driver of myofibroblast differentiation. TGF-β signals through transmembrane receptor serine/threonine kinases that phosphorylate Smad transcription factors (Smad2/3) leading to activation of transcription of target genes. Heterotrimeric G proteins mediate distinct signaling from seven-transmembrane G protein coupled receptors, which are not known to be linked to Smad activation. We tested whether G protein signaling plays any role in TGF-β-induced myofibroblast differentiation, using primary cultured human lung fibroblasts. Activation of Gαs by cholera toxin blocked TGF-β-induced myofibroblast differentiation without affecting Smad2/3 phosphorylation. Neither inhibition of Gαi by pertussis toxin nor siRNA-mediated combined knockdown of Gαq and Gα11 had a significant effect on TGF-β-induced myofibroblast differentiation. In contrast, combined knockdown of Gα12 and Gα13 significantly inhibited TGF-β-stimulated expression of myofibroblast marker proteins (collagen-1, fibronectin, smooth-muscle α-actin), with siGα12 being significantly more potent than siGα13. Mechanistically, combined knockdown of Gα12 and Gα13 resulted in substantially reduced phosphorylation of Smad2 and Smad3 in response to TGF-β, which was accompanied by a significant decrease in the expression of TGF-β receptors (TGFBR1, TGFBR2) and of Smad3. Thus, our study uncovers a novel role of Gα12/13 proteins in the control of TGF-β signaling and myofibroblast differentiation.

Critical role of Gα12 and Gα13 proteins in TGF-β-induced myofibroblast differentiation

Myofibroblast differentiation, characterized by accumulation of cytoskeletal and extracellular matrix proteins by fibroblasts, is a key process in wound healing and pathogenesis of tissue fibrosis. Transforming growth factor-β (TGF-β) is the most powerful known driver of myofibroblast differentiation. TGF-β signals through transmembrane receptor serine/threonine kinases that phosphorylate Smad transcription factors (Smad2/3) leading to activation of transcription of target genes. Heterotrimeric G proteins mediate a distinct signaling from seven-transmembrane G protein coupled receptors, not commonly linked to Smad activation. We asked if G protein signaling plays any role in TGF-β-induced myofibroblast differentiation, using primary cultured human lung fibroblasts. Activation of Gαs by cholera toxin blocked TGF-β-induced myofibroblast differentiation without affecting Smad2/3 phosphorylation. Inhibition of Gαi by pertussis toxin, or siRNA-mediated combined knockdown of Gαq and Gα11 had no significant effect on TGF-β-induced myofibroblast differentiation. A combined knockdown of Gα12 and Gα13 resulted in a drastic inhibition of TGF-β-stimulated expression of myofibroblast marker proteins (collagen-1, fibronectin, smooth-muscle α-actin), with siGα12 being significantly more potent than siGα13. Mechanistically, a combined knockdown of Gα12 and Gα13 resulted in a substantially reduced phosphorylation of Smad2 and Smad3 in response to TGF-β, which was accompanied by a significant decrease in the expression of TGFβ receptors (TGFBR1, TGFBR2) and of Smad3 under siGα12/13 conditions. In conclusion, our study uncovers a novel role of Gα12/13 proteins in the control of TGF-β signaling and myofibroblast differentiation.

Translational studies of adrenomedullin and related peptides regarding cardiovascular diseases

Adrenomedullin (AM) is a vasodilative peptide with various physiological functions, including the maintenance of vascular tone and endothelial barrier function. AM levels are markedly increased during severe inflammation, such as that associated with sepsis; thus, AM is expected to be a useful clinical marker and therapeutic agent for inflammation. However, as the increase in AM levels in cardiovascular diseases (CVDs) is relatively low compared to that in infectious diseases, the value of AM as a marker of CVDs seems to be less important. Limitations pertaining to the administrative route and short half-life of AM in the bloodstream (<30 min) restrict the therapeutic applications of AM for CVDs. In early human studies, various applications of AM for CVDs were attempted, including for heart failure, myocardial infarction, pulmonary hypertension, and peripheral artery disease; however, none achieved success. We have developed AM as a therapeutic agent for inflammatory bowel disease in which the vasodilatory effect of AM is minimized. A clinical trial evaluating this AM formulation for acute cerebral infarction is ongoing. We have also developed AM derivatives that exhibit a longer half-life and less vasodilative activity. These AM derivatives can be administered by subcutaneous injection at long-term intervals. Accordingly, these derivatives will reduce the inconvenience in use compared to that for native AM and expand the possible applications of AM for treating CVDs. In this review, we present the latest translational status of AM and its derivatives.

Extracellular CIRP Induces an Inflammatory Phenotype in Pulmonary Fibroblasts via TLR4

Extracellular cold-inducible RNA-binding protein (eCIRP), a new damage-associated molecular pattern (DAMP), has been recently shown to play a critical role in promoting the development of bleomycin-induced pulmonary fibrosis. Although fibroblast activation is a critical component of the fibrotic process, the direct effects of eCIRP on fibroblasts have never been examined. We studied eCIRP’s role in the induction of inflammatory phenotype in pulmonary fibroblasts and its connection to bleomycin-induced pulmonary fibrosis in mice. We found that eCIRP causes the induction of proinflammatory cytokines and differentially expression-related pathways in a TLR4-dependent manner in pulmonary fibroblasts. Our analysis further showed that the accessory pathways MD2 and Myd88 are involved in the induction of inflammatory phenotype. In order to study the connection of the enrichment of these pathways in priming the microenvironment for pulmonary fibrosis, we investigated the gene expression profile of lung tissues from mice subjected to bleomycin-induced pulmonary fibrosis collected at various time points. We found that at day 14, which corresponds to the inflammatory-to-fibrotic transition phase after bleomycin injection, TLR4, MD2, and Myd88 were induced, and the transcriptome was differentially enriched for genes in those pathways. Furthermore, we also found that inflammatory cytokines gene expressions were induced, and the cellular responses to these inflammatory cytokines were differentially enriched on day 14. Overall, our results show that eCIRP induces inflammatory phenotype in pulmonary fibroblasts in a TLR4 dependent manner. This study sheds light on the mechanism by which eCIRP induced inflammatory fibroblasts, contributing to pulmonary fibrosis.

Expression of serum response factor in the lung mesenchyme is essential for development of pulmonary fibrosis

Extracellular matrix deposition characterizes idiopathic pulmonary fibrosis (IPF) and is orchestrated by myofibroblasts. The lung mesenchyme is an essential source of myofibroblasts in pulmonary fibrosis. Although the transcription factor serum response factor (SRF) has shown to be critical in the process of myofibroblast differentiation, its role in development of pulmonary fibrosis has not been determined in vivo. In this study, we observed that SRF expression localized to mesenchymal compartments, areas of dense fibrosis, and fibroblastic foci in human (IPF and normal) and bleomycin-treated mouse lungs. To determine the role of mesenchymal SRF in pulmonary fibrosis, we utilized a doxycycline-inducible, Tbx4 lung enhancer (Tbx4^LE)-driven Cre-recombinase to disrupt SRF expression in the lung mesenchyme in vivo. Doxycycline-treated Tbx4^LE-rtTA/TetO-Cre/tdTom/SRF^f,f (and controls) were treated with a single intratracheal dose of bleomycin to induce pulmonary fibrosis and examined for lung mesenchymal expansion, pulmonary fibrosis, and inflammatory response. Bleomycin-treated Tbx4^LE-rtTA/TetO-Cre/tdTom/SRF^f,f mice showed decreased numbers of Tbx4^LE-positive lung mesenchymal cells (LMCs) and collagen accumulation (via hydroxyproline assay) compared with controls. This effect was associated with SRF-null LMCs losing their proliferative and myofibroblast differentiation potential compared with SRF-positive controls. Together, these data demonstrate that SRF plays a critical role in LMC myofibroblast expansion during bleomycin-induced pulmonary fibrosis. This sets the stage for pharmacological strategies that specifically target SRF in the lung mesenchyme as a potential means of treating pulmonary fibrosis.

GPCR-mediated YAP/TAZ inactivation in fibroblasts via EPAC1/2, RAP2C, and MAP4K7

Yes-associated protein (YAP) and PDZ-binding motif (TAZ) have emerged as important regulators of pathologic fibroblast activation in fibrotic diseases. Agonism of Gαs-coupled G protein coupled receptors (GPCRs) provides an attractive approach to inhibit the nuclear localization and function of YAP and TAZ in fibroblasts that inhibits or reverses their pathological activation. Agonism of the dopamine D1 GPCR has proven effective in preclinical models of lung and liver fibrosis. However, the molecular mechanisms coupling GPCR agonism to YAP and TAZ inactivation in fibroblasts remain incompletely understood. Here, using human lung fibroblasts, we identify critical roles for the cAMP effectors EPAC1/2, the small GTPase RAP2c, and the serine/threonine kinase MAP4K7 as the essential elements in the downstream signaling cascade linking GPCR agonism to LATS1/2-mediated YAP and TAZ phosphorylation and nuclear exclusion in fibroblasts. We further show that this EPAC/RAP2c/MAP4K7 signaling cascade is essential to the effects of dopamine D1 receptor agonism on reducing fibroblast proliferation, contraction, and extracellular matrix production. Targeted modulation of this cascade in fibroblasts may prove a useful strategy to regulate YAP and TAZ signaling and fibroblast activities central to tissue repair and fibrosis.

Adrenomedullin Attenuates Inflammation in White Adipose Tissue of Obese Rats Through Receptor-Mediated PKA Pathway

OBJECTIVE

Adrenomedullin (ADM) possesses therapeutic potential for inflammatory diseases. Consequently, the effects of ADM on inflammation in visceral white adipose tissue (vWAT) of obese rats or in adipocytes were explored in this study.

METHODS

Male rats were fed a high-fat diet for 12 weeks to induce obesity, and obese rats were implanted with osmotic minipumps providing constant infusion of ADM (300 ng/kg per hour) and continued to be fed a high-fat diet for 4 weeks.

RESULTS

When compared with the control group, endogenous protein expression of ADM and ADM receptors in vWAT and in lipopolysaccharide (LPS)-treated adipocytes was markedly increased. ADM significantly decreased the protein expression of the inflammatory mediators TNFα, IL-1β, cyclooxygenase-2, and inducible nitric oxide synthase in vWAT of obese rats and in adipocytes stimulated by LPS. It also inhibited the activation of the inflammatory signaling pathways MAPK and NF-κB induced by LPS in adipocytes. These effects of ADM in adipocytes were inhibited by the administration of ADM receptor antagonist and cAMP-dependent protein kinase (PKA) activation inhibitor.

CONCLUSIONS

ADM can inhibit inflammation in WAT in obesity, which may be mediated by the activation of ADM receptors and PKA.

Hepatocyte Growth Factor Secreted from Human Adipose-Derived Stem Cells Inhibits Fibrosis in Hypertrophic Scar Fibroblasts

AIMS

To study the effect of Adipose-derived stem cells (ADSCs) on fibrosis of hypertrophic scar-derived fibroblasts (HSFs) and its concrete mechanism.

BACKGROUND

ADSCs have been reported to reduce collagen production and fibroblast proliferation in co-culture experiments. Conditioned medium from adipose-derived stem cells (ADSCs-CM) has successfully inhibited fibrosis by decreasing the expression of collagen type І (Col1) and α-smooth muscle actin (α-SMA) in rabbit ear scar models. Hepatocyte growth factor (HGF), the primary growth factor in ADSCs-CM, has been shown to reverse fibrosis in various fibrotic diseases.

OBJECTIVE

To test the hypothesis that ADSCs inhibit fibrosis of HSFs through the secretion of HGF.

METHODS

HSFs were treated with DMEM containing 0%, 10%, 50% and 100% concentration of ADSCs-CM. The effect of ADSCs-CM on the viability was determined by cell viability assay, and the collagen production in HSFs was examined by Sirius red staining. Expression and secretion of fibrosis and degradation proteins were detected separately. After measuring the concentration of HGF in ADSCs-CM, the same number of HSFs were treated with 50% ADSCs-CM or HGF. HGF activity in ADSCs-CM was neutralized with a goat anti-human HGF antibody.

RESULTS

The results demonstrated that ADSCs-CM dose-dependently decreased cell viability, expression of fibrosis molecules, and tissue inhibitor of metalloproteinases-1 (TIMP-1), and significantly increased matrix metalloproteinase-1 (MMP-1) expression in HSFs. Collagen production and the ratio of collagen type І and type III (Col1/Col3) were also suppressed by ADSCs-CM in a dose-dependent manner. When HSFs were cultured with either 50% ADSCs-CM or HGF (1 ng/ml), a similar trend was observed in gene expression and protein secretion. Adding an HGF antibody to both groups returned protein expression and secretion to basal levels but did not significantly affect the fibrosis factors in the control group.

CONCLUSION

Our findings revealed that adipose-derived stem cell-secreted HGF effectively inhibits fibrosis-related factors and regulates extracellular matrix (ECM) remodeling in hypertrophic scar fibroblasts.

Klotho antagonizes pulmonary fibrosis through suppressing pulmonary fibroblasts activation, migration, and extracellular matrix production: a therapeutic implication for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) has been widely accepted as an aging-related fatal lung disease with a therapeutic impasse, largely a consequence of the complex and polygenic gene architecture underlying the molecular pathology of IPF. Here, by conducting an integrative network analysis on the largest IPF case-control RNA-seq dataset to date, we attributed the systems-level alteration in IPF to disruptions in a handful of biological processes including cell migration, transforming growth factor-β (TGF-β) signaling and extracellular matrix (ECM), and identified klotho (KL), a typical anti-aging molecule, as a potential master regulator of those disease-relevant processes. Following experiments showed reduced Kl in isolated pulmonary fibroblasts from bleomycin-exposed mice, and demonstrated that recombinant KL effectively mitigated pulmonary fibrosis in an ex vivo model and alleviated TGF-β-induced pulmonary fibroblasts activation, migration, and ECM production in vitro, which was partially ascribed to FOXF1 and CAV1, two highly co-expressed genes of KL in the IPF. Overall, KL appears to be a vital regulator during pulmonary fibrosis. Given that administration of exogenous KL is a feasible treatment strategy, our work highlighted a promising target gene that could be easily manipulated, leaving the field well placed to further explore the therapeutic potential of KL for IPF.

Targeting GPCR Signaling for Idiopathic Pulmonary Fibrosis Therapies

A variety of G protein-coupled receptors (GPCRs) have been implicated in the pathogenesis of pulmonary fibrosis, largely through their promotion of profibrotic fibroblast activation. By contrast, recent work has highlighted the beneficial effects of Gαs-coupled GPCRs on reducing fibroblast activation and fibrosis. This review highlights how fibrosis-promoting and -inhibiting GPCR signaling converges on downstream signaling and transcriptional effectors, and how the diversity and dynamics of GPCR expression challenge efforts to identify effective therapies for idiopathic pulmonary fibrosis (IPF). Next-generation strategies to overcome these challenges, focusing on target selection, polypharmacology, and personalized medicine approaches, are discussed as a path towards more effective GPCR-targeted therapies for pulmonary fibrosis.

Anti-fibrotic effects of tannic acid through regulation of a sustained TGF-beta receptor signaling

Background

Pulmonary fibrosis is a progressive disease characterized by structural distortion of the lungs. Transforming growth factor-beta (TGF-beta) is a key cytokine implicated in the pathogenesis of pulmonary fibrosis. TGF-beta-induced myofibroblast differentiation characterized by expression of smooth muscle alpha-actin and extracellular matrix proteins is a key process in pathogenesis of fibrotic disease. Tannic acid is a natural polyphenol with diverse applications. In this study, we investigated the effect of tannic acid on myofibroblast differentiation and pulmonary fibrosis in cultured cells and in bleomycin model of the disease.

Methods

Primary cultured human lung fibroblasts (HLF) were used. The relative levels of proteins were determined by Western blotting. HLF contraction was measured by traction microscopy. Bleomycin-induced pulmonary fibrosis in mice was used as the disease model.

Results

Tannic acid inhibited TGF-beta-induced expression of collagen-1 and smooth muscle alpha-actin (SMA) as well as force generation by HLF. Tannic acid did not affect initial phosphorylation of Smad2 in response to TGF-beta, but significantly inhibited sustained Smad2 phosphorylation, which we recently described to be critical for TGF-beta-induced myofibroblast differentiation. Accordingly, tannic acid inhibited Smad-dependent gene transcription in response to TGF-beta, as assessed using luciferase reporter for the activity of Smad-binding elements. Finally, in mouse model of bleomycin-induced pulmonary fibrosis, therapeutic application of tannic acid resulted in a significant reduction of lung fibrosis, decrease in collagen-1 content and of Smad2 phosphorylation in the lungs.

Conclusions

This study demonstrates the anti-fibrotic effect of tannic acid in vitro and in vivo through a regulation of sustained Smad2 phosphorylation.

Electronic supplementary material

The online version of this article (10.1186/s12931-019-1141-8) contains supplementary material, which is available to authorized users.

Adrenomedullin mediates pro-angiogenic and pro-inflammatory cytokines in asthma and COPD

PURPOSE

Adrenomedullin (AM) is a pluripotent peptide hormone with contradictory effects in human health and disease. In chronic inflammatory lung diseases, such as asthma and COPD, AM has been shown to inhibit inflammation and cell proliferation. In the present study, we aimed to investigate the effect of AM on pro-angiogenic and pro-inflammatory cytokines in asthma and COPD.

PATIENTS AND METHODS

Serum levels of pro-AM were measured in patients with asthma, COPD and matched controls. The effect of AM on intracellular signaling proteins and cytokine secretion was assessed in primary cultures of epithelial cells (EC) and airway smooth muscle cells (ASMC) established from endo-bronchial biopsies of patients with asthma, COPD and controls.

RESULTS

Serum pro-AM was higher in patients with asthma and COPD, compared to controls. AM stimulated cAMP in ASMC but not in EC. In EC, AM decreased Erk1/2 MAPK expression and activation but in ASMC, AM activated Erk1/2. This effect was similar in asthma, COPD and controls. AM stimulated the secretion of pro-angiogenic CXCL1 by EC of controls and CXCL5 by EC of asthma patients. AM did not affect the secretion of IL-6 or IL-8 by EC but stimulated the secretion of IL-6 by ASMC. In EC, AM inhibited the stimulatory effect of TGF-β and IL-4 on the secretion of IL-6 and IL-8 but had an additive stimulatory effect with TGF-β in ASMC.

CONCLUSIONS

These data suggest that AM mediates the secretion of pro-angiogenic and pro-inflammatory cytokines in a cell-type and/or a disease-specific way, explaining its association with clinical outcomes in COPD.

Dibutyryl-cAMP attenuates pulmonary fibrosis by blocking myofibroblast differentiation via PKA/CREB/CBP signaling in rats with silicosis

BACKGROUND

Myofibroblasts play a major role in the synthesis of extracellular matrix (ECM) and the stimulation of these cells is thought to play an important role in the development of silicosis. The present study was undertaken to investigate the anti-fibrotic effects of dibutyryl-cAMP (db-cAMP) on rats induced by silica.

METHODS

A HOPE MED 8050 exposure control apparatus was used to create the silicosis model. Rats were randomly divided into 4 groups: 1)controls for 16 w; 2)silicosis for 16 w; 3)db-cAMP pre-treatment; 4) db-cAMP post-treatment. Rat pulmonary fibroblasts were cultured in vitro and divided into 4 groups as follows: 1) controls; 2) 10^-7mol/L angiotensin II (Ang II); 3) Ang II +10^-4 mol/L db-cAMP; and 4) Ang II + db-cAMP+ 10^-6 mol/L H89. Hematoxylin-eosin (HE), Van Gieson staining and immunohistochemistry (IHC) were performed to observe the histomorphology of lung tissue. The levels of cAMP were detected by enzyme immunoassay. Double-labeling for α-SMA with Gαi3, protein kinase A (PKA), phosphorylated cAMP-response element-binding protein (p-CREB), and p-Smad2/3 was identified by immunofluorescence staining. Protein levels were detected by Western blot analysis. The interaction between CREB-binding protein (CBP) and Smad2/3 and p-CREB were measured by co-immunoprecipitation (Co-IP).

RESULTS

Db-cAMP treatment reduced the number and size of silicosis nodules, inhibited myofibroblast differentiation, and extracellular matrix deposition in vitro and in vivo. In addition, db-cAMP regulated Gαs protein and inhibited expression of Gαi protein, which increased endogenous cAMP. Db-cAMP increased phosphorylated cAMP-response element-binding protein (p-CREB) via protein kinase A (PKA) signaling, and decreased nuclear p-Smad2/3 binding with CREB binding protein (CBP), which reduced activation of p-Smads in fibroblasts induced by Ang II.

CONCLUSIONS

This study showed an anti-silicotic effect of db-cAMP that was mediated via PKA/p-CREB/CBP signaling. Furthermore, the findings offer novel insight into the potential use of cAMP signaling for therapeutic strategies to treat silicosis.

Downregulation of TGF-β Receptor-2 Expression and Signaling through Inhibition of Na/K-ATPase

Transforming growth factor-beta (TGF-β) is a multi-functional cytokine implicated in the control of cell growth and differentiation. TGF-β signals through a complex of TGF-β receptors 1 and 2 (TGFβR1 and TGFβR2) that phosphorylate and activate Smad2/3 transcription factors driving transcription of the Smad-target genes. The Na+/K+-ATPase is an integral plasma membrane protein critical for maintaining the electro-chemical gradient of Na+ and K+ in the cell. We found that inhibition of the Na+/K+ ATPase by ouabain results in a dramatic decrease in the expression of TGFβR2 in human lung fibrobalsts (HLF) at the mRNA and protein levels. This was accompanied by inhibition of TGF-β-induced Smad phosphorylation and the expression of TGF-β target genes, such as fibronectin and smooth muscle alpha-actin. Inhibition of Na+/K+ ATPase by an alternative approach (removal of extracellular potassium) had a similar effect in HLF. Finally, treatment of lung alveolar epithelial cells (A549) with ouabain also resulted in the downregulation of TGFβR2, the inhibition of TGF-β-induced Smad phosphorylation and of the expression of mesenchymal markers, vimentin and fibronectin. Together, these data demonstrate a critical role of Na+/K+-ATPase in the control of TGFβR2 expression, TGF-β signaling and cell responses to TGF-β.

Regulation of myofibroblast differentiation by cardiac glycosides

Myofibroblast differentiation is a key process in pathogenesis of fibrotic diseases. Cardiac glycosides (ouabain, digoxin) inhibit Na(+)-K(+)-ATPase, resulting in increased intracellular [Na(+)]-to-[K(+)] ratio in cells. Microarray analysis suggested that increased intracellular [Na(+)]/[K(+)] ratio may promote the expression of cyclooxygenase-2 (COX-2), a critical enzyme in the synthesis of prostaglandins. Given antifibrotic effects of prostaglandins through activation of protein kinase A (PKA), we examined if cardiac glycosides stimulate COX-2 expression in human lung fibroblasts and how they affect myofibroblast differentiation. Ouabain stimulated a profound COX-2 expression and a sustained PKA activation, which was blocked by COX-2 inhibitor or by COX-2 knockdown. Ouabain-induced COX-2 expression and PKA activation were abolished by the inhibitor of the Na(+)/Ca(2+) exchanger, KB-R4943. Ouabain inhibited transforming growth factor-β (TGF-β)-induced Rho activation, stress fiber formation, serum response factor activation, and the expression of smooth muscle α-actin, collagen-1, and fibronectin. These effects were recapitulated by an increase in intracellular [Na(+)]/[K(+)] ratio through the treatment of cells with K(+)-free medium or with digoxin. Although inhibition of COX-2 or of the Na(+)/Ca(2+) exchanger blocked ouabain-induced PKA activation, this failed to reverse the inhibition of TGF-β-induced Rho activation or myofibroblast differentiation by ouabain. Together, these data demonstrate that ouabain, through the increase in intracellular [Na(+)]/[K(+)] ratio, drives the induction of COX-2 expression and PKA activation, which is accompanied by a decreased Rho activation and myofibroblast differentiation in response to TGF-β. However, COX-2 expression and PKA activation are not sufficient for inhibition of the fibrotic effects of TGF-β by ouabain, suggesting that additional mechanisms must exist.

Divergent fibroblast growth factor signaling pathways in lung fibroblast subsets: where do we go from here?

Lung fibroblasts play a key role in postnatal lung development, namely, the formation of the alveolar gas exchange units, through the process of secondary septation. Although evidence initially highlighted roles for fibroblasts in the production and remodeling of the lung extracellular matrix, more recent studies have described the presence of different fibroblast subsets in the developing lung. These subsets include myofibroblasts and lipofibroblasts and their precursors. These cells are believed to play different roles in alveologenesis and are localized to different regions of the developing septa. The precise roles played by these different fibroblast subsets remain unclear. Understanding the signaling pathways that control the discrete functions of these fibroblast subsets would help to clarify the roles and the regulation of lung fibroblasts during lung development. Here, we critically evaluate a recent report that described divergent fibroblast growth factor (FGF) signaling pathways in two different subsets of lung fibroblasts that express different levels of green fluorescent protein (GFP) driven by the platelet-derived growth factor receptor-α promoter. The GFP expression was used as a surrogate for lipofibroblasts (GFP(low)) and myofibroblasts (GFP(high)). It was suggested that Fgf10/Fgf1 and Fgf18/Fgfr3 autocrine pathways may be operative in GFP(low) and GFP(high) cells, respectively, and that these pathways might regulate the proliferation and migration of different fibroblast subsets during alveologenesis. These observations lay important groundwork for the further exploration of FGF function during normal lung development, as well as in aberrant lung development associated with bronchopulmonary dysplasia.

Involvement of collagen-binding heat shock protein 47 in scleroderma-associated fibrosis

Uncontrolled fibrosis of skin and internal organs is the main characteristic of scleroderma, and collagen is a major extracellular matrix protein that deposits in the fibrotic organs. As the chaperone of collagen, heat shock protein 47 (HSP47) is closely related with the development of fibrosis. To explore the potential function of HSP47 in the pathogenesis of scleroderma, the clinical, in vivo and in vitro studies were performed. In clinical, the increased mRNA level of HSP47 was observed in the skin fibroblasts and PBMC from scleroderma patients, and the enhanced protein level of HSP47 was also detected in the skin biopsy and plasma of the above patients. Unexpectedly, the enhanced levels of HSP47 were positively correlated with the presence of anti-centromere antibody in scleroderma patients. Moreover, a high expression of HSP47 was found in the skin lesion of BLM-induced scleroderma mouse model. Further in vitro studies demonstrated that HSP47 knockdown could block the intracellular and extracellular collagen over-productions induced by exogenous TGF-β. Therefore, the results in this study provide direct evidence that HSP47 is involved in the pathogenesis of scleroderma. The high expression of HSP47 can be detected in the circulatory system of scleroderma patients, indicating that HSP47 may become a pathological marker to assess the progression of scleroderma, and also explain the systemic fibrosis of scleroderma. Meanwhile, collagen over-expression is blocked by HSP47 knockdown, suggesting the possibility that HSP47 can be a potential therapeutic target for scleroderma.

Megakaryoblastic leukemia-1 is required for the development of bleomycin-induced pulmonary fibrosis

BACKGROUND

Fibrosing disorders of the lung, such as idiopathic pulmonary fibrosis, are characterized by progressive extracellular matrix accumulation that is driven by myofibroblasts. The transcription factor megakaryoblastic leukemia-1 (MKL1) mediates myofibroblast differentiation in response to several profibrotic stimuli, but the role it plays in mediating pulmonary fibrosis has not been fully elucidated. In this study, we utilized mice that had a germline deletion of MKL1 (MKL1 (-,-)) to determine the role that MKL1 plays in the development of bleomycin-induced pulmonary fibrosis.

METHODS

Bleomycin or normal saline were intratracheally delivered to 9 to 12 week old female MKL1 (+,+) and MKL1 (-,-) mice. Mice were assessed for weight loss and survival to 28 days. Inflammatory responses were assessed through bronchoalveolar lavage at days 3 and 7 post-treatment. The development of pulmonary fibrosis was characterized using hydroxyproline assay and histological staining. MKL1 (+,+) and MKL1 (-,-) mouse lung fibroblasts were isolated to compare morphologic, gene expression and functional differences.

RESULTS

MKL1 (-,-) mice demonstrated increased survival, attenuated weight loss, and decreased collagen accumulation compared to wild-type animals 28-days after intratracheal instillation of bleomycin. Histological analysis demonstrated decreased trichrome, smooth muscle α-actin, and fibronectin staining in MKL1(-,-) mice compared to MKL1 (+,+) controls. Differential cell counts from bronchoalveolar lavage demonstrated that there was attenuated neutrophilia 3 days after bleomycin administration, but no difference at day 7. Isolated mouse lung fibroblasts from MKL1 (-,-) mice had decreased contractility and deposited less fibronectin matrix compared to wild-type controls, suggesting a defect in key remodeling functions.

CONCLUSIONS

Altogether, these data demonstrate that MKL1 plays a significant role in mediating the fibrotic response to bleomycin injury. Loss of MKL1 attenuated early neutrophil influx, as well as myofibroblast-mediated remodeling. Targeting MKL1 activity may therefore be a useful strategy in treating pulmonary fibrosis.

Increased expression of bone morphogenetic protein-7 and its related pathway provides an anti-fibrotic effect on silica induced fibrosis in vitro

BMP-7 exerts an inhibitory effect on silica induced fibrosis in RLE-6TN cells via suppressing TGF-β signaling and activating BMP signaling.

A critical review of the American Journal of Physiology-Lung Cellular and Molecular Physiology: 2012-2015

I have had the privilege of serving as Editor-in-Chief of the American Journal of Physiology: Lung Cellular and Molecular Physiology from 1/1/2012 to 1/1/2015 and have been reappointed for another 3-year term. When I took over as editor, I published an editorial in AJP-Lung in which I highlighted my vision and outlined the tasks to be accomplished to transform AJP-Lung into "The best place to publish basic, translational, and hypothesis-driven clinical lung research." Herein I review our accomplishments during the first term. As promised, we review each article submitted to this journal and our reviews always help the quality and impact of every paper. We recognized the contributions of junior authors by establishing a number of awards and increased the visibility of AJP-Lung by establishing Facebook and Blog electronic pages and sponsoring symposia in scientific meetings. Our impact factor increased from 3.523 in 2011 to 4.041 in 2012 and, thanks to our calls for papers, we are receiving large numbers of high-quality papers in all aspects of pulmonary cell biology and lung diseases. The best is yet to come.

Adrenomedullin alleviates pulmonary artery collagen accumulation in rats with pulmonary hypertension induced by high blood flow

Collagen accumulation is one of the important pathologic changes in the development of pulmonary hypertension. Previous research showed that adrenomedullin (ADM) mitigates the development of pulmonary hypertension. The present study explored the role of ADM in the development of pulmonary artery collagen accumulation induced by high pulmonary blood flow, by investigating the effect of ADM [1.5 μg/(kg h)] subcutaneously administered by mini-osmotic pump on pulmonary hemodynamics, pulmonary vascular structure and pulmonary artery collagen accumulation and synthesis in rats with high pulmonary blood flow induced by aortocaval shunting. The results showed that ADM significantly decreased mean pulmonary artery pressure (mPAP) and the ratio of right ventricular mass to left ventricular plus septal mass [RV/(LV+SP)], attenuated the muscularization of small pulmonary vessels and relative medial thickness (RMT) of pulmonary arteries in rats with high pulmonary blood flow. Meanwhile, ADM ameliorated pulmonary artery collagen deposition represented by a decrease in lung tissue hydroxyproline, collagens I and III content and pulmonary artery collagens I and III expression, reduced collagen synthesis represented by a decrease in lung tissue procollagens I and III mRNA expression. The results suggest that ADM plays a protective role in the development of pulmonary hypertension induced by high blood flow, by inhibiting pulmonary procollagen synthesis and alleviating pulmonary artery collagen accumulation.

Antifibrotic effects of noscapine through activation of prostaglandin E2 receptors and protein kinase A

Myofibroblast differentiation is a key process in the pathogenesis of fibrotic disease. We have shown previously that differentiation of myofibroblasts is regulated by microtubule polymerization state. In this work, we examined the potential antifibrotic effects of the antitussive drug, noscapine, recently found to bind microtubules and affect microtubule dynamics. Noscapine inhibited TGF-β-induced differentiation of cultured human lung fibroblasts (HLFs). Therapeutic noscapine treatment resulted in a significant attenuation of pulmonary fibrosis in the bleomycin model of the disease. Noscapine did not affect gross microtubule content in HLFs, but inhibited TGF-β-induced stress fiber formation and activation of serum response factor without affecting Smad signaling. Furthermore, noscapine stimulated a rapid and profound activation of protein kinase A (PKA), which mediated the antifibrotic effect of noscapine in HLFs, as assessed with the PKA inhibitor, PKI. In contrast, noscapine did not activate PKA in human bronchial or alveolar epithelial cells. Finally, activation of PKA and the antifibrotic effect of noscapine in HLFs were blocked by the EP2 prostaglandin E2 receptor antagonist, PF-04418948, but not by the antagonists of EP4, prostaglandin D2, or prostacyclin receptors. Together, we demonstrate for the first time the antifibrotic effect of noscapine in vitro and in vivo, and we describe a novel mechanism of noscapine action through EP2 prostaglandin E2 receptor-mediated activation of PKA in pulmonary fibroblasts.