Loss of epithelial Gq and G11 signaling inhibits TGFβ production but promotes IL-33-mediated macrophage polarization and emphysema

Adenosine receptor signalling as a driver of pulmonary fibrosis

Pulmonary fibrosis is a debilitating and life-limiting lung condition in which the damage- response mechanisms of mixed-population cells within the lungs go awry. The tissue microenvironment is drastically remodelled by aberrantly activated fibroblasts which deposit ECM components into the surrounding lung tissue, detrimentally affecting lung function and capacity for gas exchange. Growing evidence suggests a role for adenosine signalling in the pathology of tissue fibrosis in a variety of organs, including the lung, but the molecular pathways through which this occurs remain largely unknown. This review explores the role of adenosine in fibrosis and evaluates the contribution of the different adenosine receptors to fibrogenesis. Therapeutic targeting of the adenosine receptors is also considered, along with clinical observations pointing towards a role for adenosine in fibrosis. In addition, the interaction between adenosine signalling and other profibrotic signalling pathways, such as TGFβ1 signalling, is discussed.

Stretch regulates alveologenesis and homeostasis via mesenchymal Gαq/11-mediated TGFβ2 activation

Alveolar development and repair require tight spatiotemporal regulation of numerous signalling pathways that are influenced by chemical and mechanical stimuli. Mesenchymal cells play key roles in numerous developmental processes. Transforming growth factor-β (TGFβ) is essential for alveologenesis and lung repair, and the G protein α subunits Gαq and Gα11 (Gαq/11) transmit mechanical and chemical signals to activate TGFβ in epithelial cells. To understand the role of mesenchymal Gαq/11 in lung development, we generated constitutive (Pdgfrb-Cre+/-;Gnaqfl/fl;Gna11-/-) and inducible (Pdgfrb-Cre/ERT2+/-;Gnaqfl/fl;Gna11-/-) mesenchymal Gαq/11 deleted mice. Mice with constitutive Gαq/11 gene deletion exhibited abnormal alveolar development, with suppressed myofibroblast differentiation, altered mesenchymal cell synthetic function, and reduced lung TGFβ2 deposition, as well as kidney abnormalities. Tamoxifen-induced mesenchymal Gαq/11 gene deletion in adult mice resulted in emphysema associated with reduced TGFβ2 and elastin deposition. Cyclical mechanical stretch-induced TGFβ activation required Gαq/11 signalling and serine protease activity, but was independent of integrins, suggesting an isoform-specific role for TGFβ2 in this model. These data highlight a previously undescribed mechanism of cyclical stretch-induced Gαq/11-dependent TGFβ2 signalling in mesenchymal cells, which is imperative for normal alveologenesis and maintenance of lung homeostasis.

The IL-33:ST2 axis is unlikely to play a central fibrogenic role in idiopathic pulmonary fibrosis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a devastating interstitial lung disease (ILD) with limited treatment options. Interleukin-33 (IL-33) is proposed to play a role in the development of IPF however the exclusive use of prophylactic dosing regimens means that the therapeutic benefit of targeting this cytokine in IPF is unclear.

METHODS

IL-33 expression was assessed in ILD lung sections and human lung fibroblasts (HLFs) by immunohistochemistry and gene/protein expression and responses of HLFs to IL-33 stimulation measured by qPCR. In vivo, the fibrotic potential of IL-33:ST2 signalling was assessed using a murine model of bleomycin (BLM)-induced pulmonary fibrosis and therapeutic dosing with an ST2-Fc fusion protein. Lung and bronchoalveolar lavage fluid were collected for measurement of inflammatory and fibrotic endpoints. Human precision-cut lung slices (PCLS) were stimulated with transforming growth factor-β (TGFβ) or IL-33 and fibrotic readouts assessed.

RESULTS

IL-33 was expressed by fibrotic fibroblasts in situ and was increased by TGFβ treatment in vitro. IL-33 treatment of HLFs did not induce IL6, CXCL8, ACTA2 and COL1A1 mRNA expression with these cells found to lack the IL-33 receptor ST2. Similarly, IL-33 stimulation had no effect on ACTA2, COL1A1, FN1 and fibronectin expression by PCLS. Despite having effects on inflammation suggestive of target engagement, therapeutic dosing with the ST2-Fc fusion protein failed to reduce BLM-induced fibrosis measured by hydroxyproline content or Ashcroft score.

CONCLUSIONS

Together these findings suggest the IL-33:ST2 axis does not play a central fibrogenic role in the lungs with therapeutic blockade of this pathway unlikely to surpass the current standard of care for IPF.

Complex roles of TGF-β signaling pathways in lung development and bronchopulmonary dysplasia

As survival of extremely preterm infants continues to improve, there is also an associated increase in bronchopulmonary dysplasia (BPD), one of the most significant complications of preterm birth. BPD development is multifactorial resulting from exposure to multiple antenatal and postnatal stressors. BPD has both short-term health implications and long-term sequelae including increased respiratory, cardiovascular, and neurological morbidity. Transforming growth factor β (TGF-β) is an important signaling pathway in lung development, organ injury, and fibrosis and is implicated in the development of BPD. This review provides a detailed account on the role of TGF-β in antenatal and postnatal lung development, the effect of known risk factors for BPD on the TGF-β signaling pathway, and how medications currently in use or under development, for the prevention or treatment of BPD, affect TGF-β signaling.

MicroRNA Let-7 Induces M2 Macrophage Polarization in COPD Emphysema Through the IL-6/STAT3 Pathway

Background

M2 polarized macrophages are involved in the occurrence and development of emphysema in COPD patients. However, the molecular mechanism of M2 macrophage polarization is still unclear. This study investigated the molecular mechanism of let-7 differentially expressed in bronchial epithelial cells of COPD patients participating in COPD emphysema by regulating the expression of IL-6 and inducing M2 polarization of alveolar macrophages (AM).

Materials and Methods

We measured let-7c expression in human lung tissue, serum and the lung tissue of cigarette smoke (CS)-exposed mice by qRT‒PCR. We observed the M1/M2 AM polarization in the lungs of COPD patients and COPD model mice by immunofluorescence analysis. Western blotting was used to determine the expression of MMP9/12 in the lung tissue of COPD patients and CS-exposed mice. An in vitro experiment was performed to determine the molecular mechanism of let-7c-induced macrophage polarization.

Results

Let-7c expression was downregulated in COPD patients, CS-exposed mice, and CS extract (CSE)-treated human bronchial epithelial (HBE) cells. AMs in COPD patients and CS-exposed mice were dominated by the M2 type, and the release of MMP9/12 was increased. In vitro, the transfection of mimics overexpressing let-7 or the use of tocilizumab to block signal transduction between HBE cells and macrophages inhibited the IL-6/STAT3 pathway. M2 macrophage polarization was inhibited, and MMP9/12 release was reduced.

Conclusion

Our results indicate that CS decreased let-7c expression in HBE cells, and M2 AM polarization was dominant in COPD. In HBE cells, let-7c could inhibit M2 polarization of AMs through the IL-6/STAT3 pathway, providing potential diagnostic and therapeutic value for slowing COPD emphysema.

The Controversial Role of IL-33 in Lung Cancer

Interleukin-33 (IL-33) belongs to the interleukin-1 (IL-1) family, and its structure is similar to IL-18. When cells are damaged or undergo necrosis, mature form of IL-33 is secreted as a cytokine, which can activate the immune system and provide danger signals. The IL-33/ST2 signaling pathway is composed of IL-33, suppression of tumorigenicity 2 (ST2), and IL-1 receptor accessory protein (IL-1RAcP). IL-33 has been reported to be strongly associated with lung cancer progression, and can exhibit opposite effects on lung cancer under different conditions. In this review, we have summarized the structure and basic functions of IL-33, its possible function in immune regulation, and its role in pulmonary fibrosis as well as in lung cancer. We have highlighted the dual regulation of IL-33 in lung cancer and proposed potential lung cancer treatment regimens, especially new immunotherapies, based on its mechanism of action.

Lysyl oxidase-like 2 is increased in asthma and contributes to asthmatic airway remodelling

Background

Airway smooth muscle (ASM) cells are fundamental to asthma pathogenesis, influencing bronchoconstriction, airway hyperresponsiveness and airway remodelling. The extracellular matrix (ECM) can influence tissue remodelling pathways; however, to date no study has investigated the effect of ASM ECM stiffness and cross-linking on the development of asthmatic airway remodelling. We hypothesised that transforming growth factor-β (TGF-β) activation by ASM cells is influenced by ECM in asthma and sought to investigate the mechanisms involved.

Methods

This study combines in vitro and in vivo approaches: human ASM cells were used in vitro to investigate basal TGF-β activation and expression of ECM cross-linking enzymes. Human bronchial biopsies from asthmatic and nonasthmatic donors were used to confirm lysyl oxidase like 2 (LOXL2) expression in ASM. A chronic ovalbumin (OVA) model of asthma was used to study the effect of LOXL2 inhibition on airway remodelling.

Results

We found that asthmatic ASM cells activated more TGF-β basally than nonasthmatic controls and that diseased cell-derived ECM influences levels of TGF-β activated. Our data demonstrate that the ECM cross-linking enzyme LOXL2 is increased in asthmatic ASM cells and in bronchial biopsies. Crucially, we show that LOXL2 inhibition reduces ECM stiffness and TGF-β activation in vitro, and can reduce subepithelial collagen deposition and ASM thickness, two features of airway remodelling, in an OVA mouse model of asthma.

Conclusion

These data are the first to highlight a role for LOXL2 in the development of asthmatic airway remodelling and suggest that LOXL2 inhibition warrants further investigation as a potential therapy to reduce remodelling of the airways in severe asthma.

Novel role for matrix cross-linking enzyme LOXL2 in asthmatic airway remodelling: LOXL2 is increased in #asthma but LOXL2 inhibition reduces matrix stiffness in airway smooth muscle cells and reduces remodelling in vivohttps://bit.ly/3FnzGb3

Inhibition of RhoA/MRTF-A signaling alleviates nucleus pulposus fibrosis induced by mechanical stress overload

PURPOSE/AIM

: Intervertebral disc degeneration (IDD) is the leading cause of lower back pain, and clinically useful drugs for IDD are unavailable. Mechanical stress overload-induced fibrosis plays a critical role in IDD. RhoA/MRTF-A signaling is known to regulate tissue fibrosis; however, the effect of RhoA/MRTF-A on the development of IDD is unclear.

MATERIALS AND METHODS

: The expression of aggrecan, collagen I, collagen II, MMP-12, CTGF, and MRTF-A in nucleus pulposus (NP) samples from IDD patients and controls was detected by immunohistochemical staining. Primary nucleus pulposus cells (NPCs) were isolated and cultured to establish an overload strain model treated with or without CCG-1423. The protein levels of RhoA, ROCK2, MRTF-A, CTGF, and MMP-12 as well as fibrosis-associated proteins were detected by western blotting and immunofluorescence.

RESULTS

: Collagen I, MMP-12, and CTGF were significantly upregulated, and aggrecan and collagen II were significantly downregulated in the IDD samples. The cellular localization of MRTF-A was associated with intervertebral disc (IVD) degeneration. Overloaded strain enhanced the nuclear translocation of MRTF-A and changed the NPC morphology from spindle-shaped to long strips. Additional experiments showed that RhoA, ROCK2, MRTF-A, SRF, MMP-12, and CTGF were upregulated; however, aggrecan and collagen II were downregulated in NPCs under overload strain. CCG-1423, a RhoA/MRTF-A pathway inhibitor, reversed strain-induced fibrosis.

CONCLUSION

: Mechanical stress activates RhoA/MRTF-A signaling to promote extracellular matrix (ECM) degeneration in the NP, which is associated with the development of IDD. Our findings suggest that the RhoA/MRTF-A inhibitor CCG-1423 can alleviate NPC degeneration caused by overload stress and has potential as a therapeutic agent for IDD.

Pathobiology of Airway Remodeling in Asthma: The Emerging Role of Integrins

Airway remodeling is a complex clinical feature of asthma that involves long-term disruption and modification of airway architecture, which contributes significantly to airway hyperresponsiveness (AHR) and lung function decline. It is characterized by thickening of the airway smooth muscle layer, deposition of a matrix below the airway epithelium, resulting in subepithelial fibrosis, changes within the airway epithelium, leading to disruption of the barrier, and excessive mucous production and angiogenesis within the airway wall. Airway remodeling contributes to stiffer and less compliant airways in asthma and leads to persistent, irreversible airflow obstruction. Current asthma treatments aim to reduce airway inflammation and exacerbations but none are targeted towards airway remodeling. Inhibiting the development of airway remodeling or reversing established remodeling has the potential to dramatically improve symptoms and disease burden in asthmatic patients. Integrins are a family of transmembrane heterodimeric proteins that serve as the primary receptors for extracellular matrix (ECM) components, mediating cell-cell and cell-ECM interactions to initiate intracellular signaling cascades. Cells present within the lungs, including structural and inflammatory cells, express a wide and varying range of integrin heterodimer combinations and permutations. Integrins are emerging as an important regulator of inflammation, repair, remodeling, and fibrosis in the lung, particularly in chronic lung diseases such as asthma. Here, we provide a comprehensive summary of the current state of knowledge on integrins in the asthmatic airway and how these integrins promote the remodeling process, and emphasize their potential involvement in airway disease.

Level of serum IL-33 and emphysema paraseptal in clove cigarette smoker with spontaneous pneumothorax: A case report

A young male clove cigarette smoker experienced spontaneous pneumothorax and later paraseptal emphysema was detected on high-resolution computed tomography (HRCT) scan without respiratory symptoms. Smoking is a known risk factor for emphysema. Paraseptal emphysema is a type of emphysema that rarely causes respiratory symptoms, nevertheless, usually accompanied by spontaneous pneumothorax. Interleukin 33 (IL-33) is an alarmin cytokine that belongs to the IL-1 family. The effects of IL-33 depend on its structure. In its mature form, it is a cytokine alarmin that binds to ST2 (suppression of tumorigenicity) receptors on the surface of macrophages and innate immune cells to drive Th1/Th2 immune responses, causing oxidative stress, and increased IL-33 production causes polarization of alveolar macrophages to an M2 phenotype. In this study, long-term exposure to clove cigarette smoke caused an increased serum level of IL-33 (43.72 pg/mL) and paucigranulocytic airway inflammation. In paucigranulocytic inflammation, IL-33 is involved in lung parenchymal damage presumably through oxidative stress, activation of alveolar macrophage and increased MMP12 secretion, resulting in alveolar destruction and airspace enlargement.

Cell-permeable high-affinity tracers for Gq proteins provide structural insights, reveal distinct binding kinetics and identify small molecule inhibitors

Background and Purpose

G proteins are intracellular switches that transduce and amplify extracellular signals from GPCRs. The G_q protein subtypes, which are coupled to PLC activation, can act as oncogenes, and their expression was reported to be up‐regulated in cancer and inflammatory diseases. G_q inhibition may be an efficient therapeutic strategy constituting a new level of intervention. However, diagnostic tools and therapeutic drugs for G_q proteins are lacking.

Experimental Approach

We have now developed G_q‐specific, cell‐permeable ³H‐labelled high‐affinity probes based on the macrocyclic depsipeptides FR900359 (FR) and YM‐254890 (YM). The tracers served to specifically label and quantify G_q proteins in their native conformation in cells and tissues with high accuracy.

Key Results

FR and YM displayed low nanomolar affinity for Gα_q, Gα₁₁ and Gα₁₄ expressed in CRISPR/Cas9 Gα_q‐knockout cells, but not for Gα₁₅. The two structurally very similar tracers showed strikingly different dissociation kinetics, which is predicted to result in divergent biological effects. Computational studies suggested a “dowel” effect of the pseudoirreversibly binding FR. A high‐throughput binding assay led to the discovery of novel G_q inhibitors, which inhibited G_q signalling in recombinant cells and primary murine brown adipocytes, resulting in enhanced differentiation.

Conclusions and Implications

The Gq protein inhibitors YM and FR are pharmacologically different despite similar structures. The new versatile tools and powerful assays will contribute to the advancement of the rising field of G protein research.

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.

Transcriptomics Analysis Reveals New Insights into the Roles of Notch1 Signaling on Macrophage Polarization

Naïve macrophages (Mφ) polarize in response to various environmental cues to a spectrum of cells that have distinct biological functions. The extreme ends of the spectrum are classified as M1 and M2 macrophages. Previously, we demonstrated that Notch1 deficiency promotes Tgf-β2 dependent M2-polarization in a mouse model of abdominal aortic aneurysm. The present studies aimed to characterize the unique set of genes regulated by Notch1 signaling in macrophage polarization. Bone marrow derived macrophages isolated from WT or Notch1+/- mice (n = 12) were differentiated to Mφ, M1 or M2-phenotypes by 24 h exposure to vehicle, LPS/IFN-γ or IL4/IL13 respectively and total RNA was subjected to RNA-Sequencing (n = 3). Bioinformatics analyses demonstrated that Notch1 haploinsufficiency downregulated the expression of 262 genes at baseline level, 307 genes with LPS/IFN-γ and 254 genes with IL4/IL13 treatment. Among these, the most unique genes downregulated by Notch1 haploinsufficiency included fibromodulin (Fmod), caspase-4, Has1, Col1a1, Alpl and Igf. Pathway analysis demonstrated that extracellular matrix, macrophage polarization and osteogenesis were the major pathways affected by Notch1 haploinsufficiency. Gain and loss-of-function studies established a strong correlation between Notch1 haploinsufficiency and Fmod in regulating Tgf-β signaling. Collectively, our studies suggest that Notch1 haploinsufficiency increases M2 polarization through these newly identified genes.

Loss of the adhesion G-protein coupled receptor ADGRF5 in mice induces airway inflammation and the expression of CCL2 in lung endothelial cells

Background

Adhesion G-protein coupled receptor F5 (ADGRF5) was recently identified as an essential regulator of pulmonary surfactant homeostasis in alveolar type II cells. We previously showed that in addition to abnormal surfactant accumulation, Adgrf5-deficient (Adgrf5^−/−) mice exhibit emphysema-like signs, suggesting a possible role for ADGRF5 in immune regulation. Here, we extended the phenotypic analysis of Adgrf5^−/− mice to help understand its biological role in the lung, and especially in immune regulation.

Methods

Histological features of lungs were evaluated by Alcian blue and Masson’s trichrome staining. Quantitative real-time PCR (qPCR) and western blot analyses were performed to analyze the differential expression of genes/proteins related to airway inflammation in lungs between wildtype and Adgrf5^−/− mice. Acid–base status was assessed by performing blood gas tests and urine pH measurements. Inflammatory cell counting was performed using Giemsa-stained bronchoalveolar lavage cells. Serum IgE concentrations were determined by enzyme-linked immunosorbent assay. The expression of Ccl2, S100a8, S100a9, and Saa3 in primary lung endothelial cells (ECs) was determined by qPCR and/or western blotting. Finally, the effect of administrating RS504393 to 2-week-old Adgrf5^−/− mice on gene expression in the lungs was analyzed by qPCR.

Results

Adgrf5^−/− mice exhibited several features of chronic airway inflammation (mucous cell metaplasia, mucus hyperproduction, subepithelial fibrosis, respiratory acidosis, high serum IgE, mast cell accumulation, and neutrophilia) in parallel with elevated expression of genes involved in mucous cell metaplasia (Muc5ac, Muc5b, Slc26a4, and Clca1), fibrosis (Tgfb1, Col1a1, Fn1, and Tnc), and type 2 immune response (Il4, Il5, Il13, IL-25, and IL-33) at 12 and/or 30 weeks of age. In contrast, mRNA expression of Ccl2, S100a8, and S100a9 was upregulated in embryonic or neonatal Adgrf5^−/− lungs as well as in lung ECs of Adgrf5^−/− mice at 1 week of age. RS504393 treatment suppressed the upregulation of S100a8, S100a9, Slc26a4, and Il5 in Adgrf5^−/− lungs.

Conclusions

Targeted disruption of ADGRF5 results in the development of airway inflammation, which is likely mediated by the type 2 immune response and possibly CCL2-mediated inflammation. ADGRF5 also has a potential role in the regulation of genes encoding CCL2 in lung ECs, thereby maintaining immune homeostasis.

Electronic supplementary material

The online version of this article (10.1186/s12931-019-0973-6) contains supplementary material, which is available to authorized users.

IL-33/ST2 Axis in Organ Fibrosis

Interleukin 33 (IL-33) is highly expressed in barrier sites, acting via the suppression of tumorigenicity 2 receptor (ST2). IL-33/ST2 axis has long been known to play a pivotal role in immunity and cell homeostasis by promoting wound healing and tissue repair. However, it is also involved in the loss of balance between extensive inflammation and tissue regeneration lead to remodeling, the hallmark of fibrosis. The aim of the current review is to critically evaluate the available evidence regarding the role of the IL-33/ST2 axis in organ fibrosis. The role of the axis in tissue remodeling is better understood considering its crucial role reported in organ development and regeneration. Generally, the IL-33/ST2 signaling pathway has mainly anti-inflammatory/anti-proliferative effects; however, chronic tissue injury is responsible for pro-fibrogenetic responses. Regarding pulmonary fibrosis mature IL-33 enhances pro-fibrogenic type 2 cytokine production in an ST2- and macrophage-dependent manner, while full-length IL-33 is also implicated in the pulmonary fibrotic process in an ST2-independent, Th2-independent fashion. In liver fibrosis, evidence indicate that when acute and massive liver damage occurs, the release of IL-33 might act as an activator of tissue-protective mechanisms, while in cases of chronic injury IL-33 plays the role of a hepatic fibrotic factor. IL-33 signaling has also been involved in the pathogenesis of acute and chronic pancreatitis. Moreover, IL-33 could be used as an early marker for ulcer-associated activated fibroblasts and myofibroblast trans-differentiation; thus one cannot rule out its potential role in inflammatory bowel disease-associated fibrosis. Similarly, the upregulation of the IL-33/ST2 axismay contribute to tubular cell injury and fibrosis via epithelial to mesenchymal transition (EMT) of various cell types in the kidneys. Of note, IL-33 exerts a cardioprotective role via ST2 signaling, while soluble ST2 has been demonstrated as a marker of myocardial fibrosis. Finally, IL-33 is a crucial cytokine in skin pathology responsible for abnormal fibroblast proliferation, leukocyte infiltration and morphologic differentiation of human endothelial cells. Overall, emerging data support a novel contribution of the IL-33/ST2 pathway in tissue fibrosis and highlight the significant role of the Th2 pattern of immune response in the pathophysiology of organ fibrosis.

Targeting G protein-coupled receptor signalling by blocking G proteins

G protein-coupled receptors (GPCRs) are the largest class of drug targets, largely owing to their druggability, diversity and physiological efficacy. Many drugs selectively target specific subtypes of GPCRs, but high specificity for individual GPCRs may not be desirable in complex multifactorial disease states in which multiple receptors may be involved. One approach is to target G protein subunits rather than the GPCRs directly. This approach has the potential to achieve broad efficacy by blocking pathways shared by multiple GPCRs. Additionally, because many GPCRs couple to multiple G protein signalling pathways, blocking specific G protein subunits can 'bias' GPCR signals by inhibiting only a subset of these signals. Molecules that target G protein α or βγ-subunits have been developed and show strong efficacy in multiple preclinical disease models and biased inhibition of G protein signalling. In this Review, we discuss the development and characterization of G protein α and βγ-subunit ligands and the preclinical evidence that this exciting new approach has potential for therapeutic efficacy in a number of indications, such as pain, thrombosis, asthma and heart failure.

Micro-RNA-1 is decreased by hypoxia and contributes to the development of pulmonary vascular remodeling via regulation of sphingosine kinase 1

Sphingosine kinase 1 (SphK1) upregulation is associated with pathologic pulmonary vascular remodeling in pulmonary arterial hypertension (PAH), but the mechanisms controlling its expression are undefined. In this study, we sought to characterize the regulation of SphK1 expression by micro-RNAs (miRs). In silico analysis of the SphK1 3'-untranslated region identified several putative miR binding sites, with miR-1-3p (miR-1) being the most highly predicted target. Therefore we further investigated the role of miR-1 in modulating SphK1 expression and characterized its effects on the phenotype of pulmonary artery smooth muscle cells (PASMCs) and the development of experimental pulmonary hypertension in vivo. Our results demonstrate that miR-1 is downregulated by hypoxia in PASMCs and can directly inhibit SphK1 expression. Overexpression of miR-1 in human PASMCs inhibits basal and hypoxia-induced proliferation and migration. Human PASMCs isolated from PAH patients exhibit reduced miR-1 expression. We also demonstrate that miR-1 is downregulated in mouse lung tissues during experimental hypoxia-mediated pulmonary hypertension (HPH), consistent with upregulation of SphK1. Furthermore, administration of miR-1 mimics in vivo prevented the development of HPH in mice and attenuated induction of SphK1 in PASMCs. These data reveal the importance of miR-1 in regulating SphK1 expression during hypoxia in PASMCs. A pivotal role is played by miR-1 in pulmonary vascular remodeling, including PASMC proliferation and migration, and its overexpression protects from the development of HPH in vivo. These studies improve our understanding of the molecular mechanisms underlying the pathogenesis of pulmonary hypertension.

Cyclic stretch induced IL-33 production through HMGB1/TLR-4 signaling pathway in murine respiratory epithelial cells

Interleukin 33 (IL-33), an inflammatory and mechanically responsive cytokine, is an important component of a TLR4-dependent innate immune process in mucosal epithelium. Although TLR4 also plays a role in sensing biomechanical stretch, a pathway of stretch-induced TLR4-dependent IL-33 biosynthesis has not been revealed. In the current study, we show that short term (6 h) cyclic stretch (CS) of cultured murine respiratory epithelial cells (MLE-12) increased intracellular IL-33 expression in a TLR4 dependent fashion. There was no detectable IL-33 in conditioned media in this interval. CS, however, increased release of the notable alarmin, HMGB1, and a neutralizing antibody (2G7) to HMGB1 completely abolished the CS mediated increase in IL-33. rHMGB1 increased IL-33 synthesis and this was partially abrogated by silencing TLR4 suggesting additional receptors for HMGB1 are involved in its regulation of IL-33. Collectively, these data reveal a HMGB1/TLR4/IL-33 pathway in the response of respiratory epithelium to mechanical stretch.

Epithelial Gpr116 regulates pulmonary alveolar homeostasis via Gq/11 signaling

Pulmonary function is dependent upon the precise regulation of alveolar surfactant. Alterations in pulmonary surfactant concentrations or function impair ventilation and cause tissue injury. Identification of the molecular pathways that sense and regulate endogenous alveolar surfactant concentrations, coupled with the ability to pharmacologically modulate them both positively and negatively, would be a major therapeutic advance for patients with acute and chronic lung diseases caused by disruption of surfactant homeostasis. The orphan adhesion GPCR GPR116 (also known as Adgrf5) is a critical regulator of alveolar surfactant concentrations. Here, we show that human and mouse GPR116 control surfactant secretion and reuptake in alveolar type II (AT2) cells by regulating guanine nucleotide-binding domain α q and 11 (Gq/11) signaling. Synthetic peptides derived from the ectodomain of GPR116 activated Gq/11-dependent inositol phosphate conversion, calcium mobilization, and cortical F-actin stabilization to inhibit surfactant secretion. AT2 cell-specific deletion of Gnaq and Gna11 phenocopied the accumulation of surfactant observed in Gpr116-/- mice. These data provide proof of concept that GPR116 is a plausible therapeutic target to modulate endogenous alveolar surfactant pools to treat pulmonary diseases associated with surfactant dysfunction.

Methods for the Assessment of Active Transforming Growth Factor-β in Cells and Tissues

The potent and pluripotent cytokine TGFβ has important roles in normal homeostasis and disease pathogenesis. Once released from cells, TGFβ exists in both latent and functionally active forms. Large amounts of latent TGFβ are secreted from cells and sequestered in extracellular matrix, only a small proportion of which is activated at any given time. Accurate assessment of TGFβ activity levels is an important measurement in biological research and requires methods distinct from measuring total levels of TGFβ expression as small changes in TGFβ activity levels could be masked by the large amounts of latent TGFβ available to be measured. In this chapter, we describe detailed experimental methods for assessing levels of active TGFβ in cells and tissues. This chapter includes methods for the assessment of TGFβ activity in cells in vitro, in ex vivo precision cut tissue, and in vivo.