Methionine aminopeptidase-2 as a selective target of myofibroblasts in pulmonary fibrosis

Increased expression of CXCL6 in secretory cells drives fibroblast collagen synthesis and is associated with increased mortality in idiopathic pulmonary fibrosis

RATIONALE

Recent data suggest that the localisation of airway epithelial cells in the distal lung in idiopathic pulmonary fibrosis (IPF) may drive pathology. We set out to discover whether chemokines expressed in these ectopic airway epithelial cells may contribute to the pathogenesis of IPF.

METHODS

We analysed whole lung and single-cell transcriptomic data obtained from patients with IPF. In addition, we measured chemokine levels in blood, bronchoalveolar lavage (BAL) of IPF patients and air-liquid interface cultures. We employed ex vivo donor and IPF lung fibroblasts and an animal model of pulmonary fibrosis to test the effects of chemokine signalling on fibroblast function.

RESULTS

By analysis of whole-lung transcriptomics, protein and BAL, we discovered that CXCL6 (a member of the interleukin-8 family) was increased in patients with IPF. Elevated CXCL6 levels in the BAL of two cohorts of patients with IPF were associated with poor survival (hazard ratio of death or progression 1.89, 95% CI 1.16-3.08; n=179, p=0.01). By immunostaining and single-cell RNA sequencing, CXCL6 was detected in secretory cells. Administration of mCXCL5 (LIX, murine CXCL6 homologue) to mice increased collagen synthesis with and without bleomycin. CXCL6 increased collagen I levels in donor and IPF fibroblasts 4.4-fold and 1.7-fold, respectively. Both silencing of and chemical inhibition of CXCR1/2 blocked the effects of CXCL6 on collagen, while overexpression of CXCR2 increased collagen I levels 4.5-fold in IPF fibroblasts.

CONCLUSIONS

CXCL6 is expressed in ectopic airway epithelial cells. Elevated levels of CXCL6 are associated with IPF mortality. CXCL6-driven collagen synthesis represents a functional consequence of ectopic localisation of airway epithelial cells in IPF.

Single-nucleus chromatin accessibility identifies a critical role for TWIST1 in idiopathic pulmonary fibrosis myofibroblast activity

BACKGROUND

In idiopathic pulmonary fibrosis (IPF), myofibroblasts are key effectors of fibrosis and architectural distortion by excessive deposition of extracellular matrix and their acquired contractile capacity. Single-cell RNA-sequencing (scRNA-seq) has precisely defined the IPF myofibroblast transcriptome, but identifying critical transcription factor activity by this approach is imprecise.

METHODS

We performed single-nucleus assay for transposase-accessible chromatin sequencing on explanted lungs from patients with IPF (n=3) and donor controls (n=2) and integrated this with a larger scRNA-seq dataset (10 IPF, eight controls) to identify differentially accessible chromatin regions and enriched transcription factor motifs within lung cell populations. We performed RNA-sequencing on pulmonary fibroblasts of bleomycin-injured Twist1-overexpressing COL1A2 Cre-ER mice to examine alterations in fibrosis-relevant pathways following Twist1 overexpression in collagen-producing cells.

RESULTS

TWIST1, and other E-box transcription factor motifs, were significantly enriched in open chromatin of IPF myofibroblasts compared to both IPF nonmyogenic (log2 fold change (FC) 8.909, adjusted p-value 1.82×10-35) and control fibroblasts (log2FC 8.975, adjusted p-value 3.72×10-28). TWIST1 expression was selectively upregulated in IPF myofibroblasts (log2FC 3.136, adjusted p-value 1.41×10- 24), with two regions of TWIST1 having significantly increased accessibility in IPF myofibroblasts. Overexpression of Twist1 in COL1A2-expressing fibroblasts of bleomycin-injured mice resulted in increased collagen synthesis and upregulation of genes with enriched chromatin accessibility in IPF myofibroblasts.

CONCLUSIONS

Our studies utilising human multiomic single-cell analyses combined with in vivo murine disease models confirm a critical regulatory function for TWIST1 in IPF myofibroblast activity in the fibrotic lung. Understanding the global process of opening TWIST1 and other E-box transcription factor motifs that govern myofibroblast differentiation may identify new therapeutic interventions for fibrotic pulmonary diseases.

Niacin Attenuates Pulmonary Hypertension Through H-PGDS in Macrophages

RATIONALE

Pulmonary arterial hypertension (PAH) is characterized by progressive pulmonary vascular remodeling, accompanied by varying degrees of perivascular inflammation. Niacin, a commonly used lipid-lowering drug, possesses vasodilating and proresolution effects by promoting the release of prostaglandin D₂ (PGD₂). However, whether or not niacin confers protection against PAH pathogenesis is still unknown.

OBJECTIVE

This study aimed to determine whether or not niacin attenuates the development of PAH and, if so, to elucidate the molecular mechanisms underlying its effects.

METHODS AND RESULTS

Vascular endothelial growth factor receptor inhibitor SU5416 and hypoxic exposure were used to induce pulmonary hypertension (PH) in rodents. We found that niacin attenuated the development of this hypoxia/SU5416-induced PH in mice and suppressed progression of monocrotaline-induced and hypoxia/SU5416-induced PH in rats through the reduction of pulmonary artery remodeling. Niacin boosted PGD₂ generation in lung tissue, mainly through H-PGDS (hematopoietic PGD₂ synthases). Deletion of H-PGDS, but not lipocalin-type PGDS, exacerbated the hypoxia/SU5416-induced PH in mice and abolished the protective effects of niacin against PAH. Moreover, H-PGDS was expressed dominantly in infiltrated macrophages in lungs of PH mice and patients with idiopathic PAH. Macrophage-specific deletion of H-PGDS markedly decreased PGD₂ generation in lungs, aggravated hypoxia/SU5416-induced PH in mice, and attenuated the therapeutic effect of niacin on PAH.

CONCLUSIONS

Niacin treatment ameliorates the progression of PAH through the suppression of vascular remodeling by stimulating H-PGDS-derived PGD₂ release from macrophages.

TNP-470 skews DC differentiation to Th1-stimulatory phenotypes and can serve as a novel adjuvant in a cancer vaccine

Fumagillin is an antiangiogenic and antineoplastic fungal natural product, and TNP-470 is one of its most potent analogs. Decades of studies revealed that TNP-470 has potent anticancer activities via destruction of neovasculature. In stark contrast, TNP-470 has been reported to suppress lymphocyte proliferation, thereby limiting its clinical potentials. In an attempt to investigate whether the similar or opposite immunomodulatory effect of TNP-470 could act on myeloid cells, we found that TNP-470 potentiates the immunogenicity of dendritic cells (DCs) toward a phenotype with T helper cell type 1 (Th1)-stimulatory features. Using DC vaccine on a murine melanoma cancer model, the TNP-470-treated DC vaccine could significantly induce tumor-specific immunogenicity and substantially enhance tumor eradication when compared with vehicle-treated DC vaccine in a prophylactic setting. Enhanced tumor-specific immunogenicity and delayed tumor progression were observed in a therapeutic setting upon the TNP-470-treated DC vaccine. Our data showed that TNP-470 potentiates Toll-like receptor signaling, including NF-κB activation, in DCs to transcriptionally activate interleukin-12 production, thus inducing a Th1-immune response. Our current study uncovers a novel immune function of TNP-470 in DCs and redefines its role as a novel class of small molecule immune adjuvant in DC-based cancer vaccine given potentiation of DC immunogenicity is a major roadblock in DC vaccine development. Our study not only provides a novel adjuvant for ex vivo-cultured patient-specific DC vaccines for cancer treatment but also discovers the distinct immunostimulatory function of TNP-470 in DCs of myeloid lineage that differs from its immunosuppressive function in lymphoid cells.

Loss of Twist1 in the Mesenchymal Compartment Promotes Increased Fibrosis in Experimental Lung Injury by Enhanced Expression of CXCL12

Idiopathic pulmonary fibrosis (IPF) is a disease characterized by the accumulation of apoptosis-resistant fibroblasts in the lung. We have previously shown that high expression of the transcription factor Twist1 may explain this prosurvival phenotype in vitro. However, this observation has never been tested in vivo. We found that loss of Twist1 in COL1A2+ cells led to increased fibrosis characterized by very significant accumulation of T cells and bone marrow-derived matrix-producing cells. We found that Twist1-null cells expressed high levels of the T cell chemoattractant CXCL12. In vitro, we found that the loss of Twist1 in IPF lung fibroblasts increased expression of CXCL12 downstream of increased expression of the noncanonical NF-κB transcription factor RelB. Finally, blockade of CXCL12 with AMD3100 attenuated the exaggerated fibrosis observed in Twist1-null mice. Transcriptomic analysis of 134 IPF patients revealed that low expression of Twist1 was characterized by enrichment of T cell pathways. In conclusion, loss of Twist1 in collagen-producing cells led to increased bleomycin-induced pulmonary fibrosis, which is mediated by increased expression of CXCL12. Twist1 expression is associated with dysregulation of T cells in IPF patients. Twist1 may shape the IPF phenotype and regulate inflammation in fibrotic lung injury.

Automated tracking of tumor-stroma morphology in microtissues identifies functional targets within the tumor microenvironment for therapeutic intervention

Cancer-associated fibroblasts (CAFs) constitute an important part of the tumor microenvironment and promote invasion via paracrine functions and physical impact on the tumor. Although the importance of including CAFs into three-dimensional (3D) cell cultures has been acknowledged, computational support for quantitative live-cell measurements of complex cell cultures has been lacking. Here, we have developed a novel automated pipeline to model tumor-stroma interplay, track motility and quantify morphological changes of 3D co-cultures, in real-time live-cell settings. The platform consists of microtissues from prostate cancer cells, combined with CAFs in extracellular matrix that allows biochemical perturbation. Tracking of fibroblast dynamics revealed that CAFs guided the way for tumor cells to invade and increased the growth and invasiveness of tumor organoids. We utilized the platform to determine the efficacy of inhibitors in prostate cancer and the associated tumor microenvironment as a functional unit. Interestingly, certain inhibitors selectively disrupted tumor-CAF interactions, e.g. focal adhesion kinase (FAK) inhibitors specifically blocked tumor growth and invasion concurrently with fibroblast spreading and motility. This complex phenotype was not detected in other standard in vitro models. These results highlight the advantage of our approach, which recapitulates tumor histology and can significantly improve cancer target validation in vitro.

Mechanical ventilation augments bleomycin-induced epithelial-mesenchymal transition through the Src pathway

Mechanical ventilation used in patients with acute respiratory distress syndrome (ARDS) can damage pulmonary epithelial cells by producing inflammatory cytokines and depositing excess collagen. Src participates in plasminogen activator inhibitor-1 (PAI-1) and transforming growth factor-β1(TGF-β1) production during the fibroproliferative phase of ARDS, which involves a process of epithelial-mesenchymal transition (EMT). The mechanisms regulating interactions between mechanical ventilation and EMT are unclear. We hypothesized that EMT induced by high-tidal volume (VT) mechanical stretch-augmented lung inflammation occurs through upregulation of the Src pathway. Five days after administering bleomycin to simulate acute lung injury (ALI), male C57BL/6 mice, either wild-type or Src-deficient, aged 3 months, weighing between 25 and 30 g, were exposed to low-VT (6 ml/kg) or high-VT (30 ml/kg) mechanical ventilation with room air for 1-5 h. Nonventilated mice were used as control subjects. We observed that high-VT mechanical ventilation increased microvascular permeability, PAI-1 and TGF-β1 protein levels, Masson's trichrome staining, extracellular collagen levels, collagen gene expression, fibroblast accumulation, positive staining of α-smooth muscle actin and type I collagen, activation of Src signaling and epithelial apoptotic cell death in wild-type mice (P<0.05). Decreased staining of the epithelial marker, Zonula occludents-1, was also observed. Mechanical stretch-augmented EMT and epithelial apoptosis were attenuated in Src-deficient mice and pharmacological inhibition of Src activity by PP2 (P<0.05). Our data suggest that high-VT mechanical ventilation-augmented EMT after bleomycin-induced ALI partially depends on the Src pathway.

Early treatment with fumagillin, an inhibitor of methionine aminopeptidase-2, prevents Pulmonary Hypertension in monocrotaline-injured rats

Pulmonary Hypertension (PH) is a pathophysiologic condition characterized by hypoxemia and right ventricular strain. Proliferation of fibroblasts, smooth muscle cells, and endothelial cells is central to the pathology of PH in animal models and in humans. Methionine aminopeptidase-2 (MetAP2) regulates proliferation in a variety of cell types including endothelial cells, smooth muscle cells, and fibroblasts. MetAP2 is inhibited irreversibly by the angiogenesis inhibitor fumagillin. We have previously found that inhibition of MetAP2 with fumagillin in bleomycin-injured mice decreased pulmonary fibrosis by selectively decreasing the proliferation of lung myofibroblasts. In this study, we investigated the role of fumagillin as a potential therapy in experimental PH. In vivo, treatment of rats with fumagillin early after monocrotaline injury prevented PH and right ventricular remodeling by decreasing the thickness of the medial layer of the pulmonary arteries. Treatment with fumagillin beginning two weeks after monocrotaline injury did not prevent PH but was associated with decreased right ventricular mass and decreased cardiomyocyte hypertrophy, suggesting a direct effect of fumagillin on right ventricular remodeling. Incubation of rat pulmonary artery smooth muscle cells (RPASMC) with fumagillin and MetAP2-targeting siRNA inhibited proliferation of RPASMC in vitro. Platelet-derived growth factor, a growth factor that is important in the pathogenesis of PH and stimulates proliferation of fibroblasts and smooth muscle cells, strongly increased expression of MetP2. By immunohistochemistry, we found that MetAP2 was expressed in the lesions of human pulmonary arterial hypertension. We propose that fumagillin may be an effective adjunctive therapy for treating PH in patients.

Cytokine-like factor 1 gene expression is enriched in idiopathic pulmonary fibrosis and drives the accumulation of CD4+ T cells in murine lungs: evidence for an antifibrotic role in bleomycin injury

Idiopathic pulmonary fibrosis (IPF) is a progressive and typically fatal lung disease. To gain insight into the pathogenesis of IPF, we reanalyzed our previously published gene expression data profiling IPF lungs. Cytokine receptor-like factor 1 (CRLF1) was among the most highly up-regulated genes in IPF lungs, compared with normal controls. The protein product (CLF-1) and its partner, cardiotrophin-like cytokine (CLC), function as members of the interleukin 6 (IL-6) family of cytokines. Because of earlier work implicating IL-6 family members in IPF pathogenesis, we tested whether CLF-1 expression contributes to inflammation in experimental pulmonary fibrosis. In IPF, we detected CLF-1 expression in both type II alveolar epithelial cells and macrophages. We found that the receptor for CLF-1/CLC signaling, ciliary neurotrophic factor receptor (CNTFR), was expressed only in type II alveolar epithelial cells. Administration of CLF-1/CLC to both uninjured and bleomycin-injured mice led to the pulmonary accumulation of CD4(+) T cells. We also found that CLF-1/CLC administration increased inflammation but decreased pulmonary fibrosis. CLF-1/CLC leads to significantly enriched expression of T-cell-derived chemokines and cytokines, including the antifibrotic cytokine interferon-γ. We propose that, in IPF, CLF-1 is a selective stimulus of type II alveolar epithelial cells and may potentially drive an antifibrotic response by augmenting both T-helper-1-driven and T-regulatory-cell-driven inflammatory responses in the lung.

Arteriolar vascular smooth muscle cell differentiation in benign nephrosclerosis

BACKGROUND

Benign nephrosclerosis (bN) is the most prevalent form of hypertensive damage in kidney biopsies. It is defined by early hyalinosis and later fibrosis of renal arterioles. Despite its high prevalence, very little is known about the contribution of arteriolar vascular smooth muscle cells (VSMCs) to bN. We examined classical and novel candidate markers of the normal contractile and the pro-fibrotic secretory phenotype of VSMCs in arterioles in bN.

METHODS

Sixty-three renal tissue specimens with bN and eight control specimens were examined by immunohistochemistry for the contractile markers caldesmon, alpha-smooth muscle actin (alpha-SMA), JunB, smoothelin and the secretory marker S100A4 and by double stains for caldesmon or smoothelin with S100A4.

RESULTS

Smoothelin immunostaining showed an inverse correlation with hyalinosis and fibrosis scores, while S100A4 correlated with fibrosis scores only. Neither caldesmon, alpha-SMA nor JunB correlated with hyalinosis or fibrosis scores. Cells in the arteriolar wall were exclusively positive either for caldesmon/smoothelin or S100A4.

CONCLUSIONS

This is the first systematic analysis of VSMC differentiation in bN. The results suggest that smoothelin is the most sensitive marker for the contractile phenotype and that S100A4 could be a novel marker for the secretory phenotype in vivo. The other markers did not seem to differentiate these phenotypes in bN. Thus, VSMC phenotype markers should be defined in the context of the vessel segment and disease under examination. S100A4 could not only be a marker of pro-fibrotic secretory VSMCs in bN but also an important mediator of arteriolar fibrosis.

New pharmacological strategies for the treatment of pulmonary fibrosis

The treatment of pulmonary fibrosis continues to pose major difficulties. Idiopathic pulmonary fibrosis (IPF), the most prevalent chronic fibrosing lung disease, is a devastating condition that carries a prognosis worse than that of many cancers. Abnormalities in multiple pathways involved in wound healing and inflammation lead to the development of this condition. High doses of corticosteroids are now contraindicated in IPF, although they have a role in other fibrosing lung diseases. More effective treatments are urgently required and a number of novel candidate therapies have been put forward, based on animal and in vitro work. As in other complex disorders, it is likely that combinations of agents, rather than single treatments, will be needed. The principle of combination therapy was recently endorsed by the guidelines of the British Thoracic Society, which make a weak recommendation for a combination of prednisolone, azathioprine and N-acetylcysteine. However, enrolment of patients into trials of new therapies is considered to be ‘best current practice’ as this offers sufferers with IPF the chance to receive new agents that may be more effective than current treatments. In pulmonary fibrotic disorders other than IPF, anti-inflammatory therapy is broadly appropriate and benefits most patients, but a clear treatment strategy is essential. The art of management is to distinguish accurately between inherently stable fibrotic disease (with treatment not required), progressive predominantly fibrotic disease (with low-dose long-term treatment warranted to retard progression) and the presence of major associated inflammation (justifying initial high-dose treatment).

Gene expression profiling of pulmonary fibrosis identifies Twist1 as an antiapoptotic molecular "rectifier" of growth factor signaling

Idiopathic pulmonary fibrosis (IPF) is a progressive and typically fatal lung disease. To gain insight into IPF pathogenesis, we performed gene expression profiling of IPF lungs. Twist1, a basic helix-loop-helix protein, was found among the most consistently and highly up-regulated genes and was expressed in nuclei of type II epithelial cells, macrophages, and fibroblasts in IPF lungs. We studied the function of Twist1 in fibroblasts further, because they are the major effector cells in this disease and persist despite an ambient proapoptotic environment. Twist1 was induced by the profibrotic growth factors (GFs) basic fibroblast growth factor, platelet-derived growth factor, and epidermal growth factor in primary rat lung fibroblasts (RLFs). Suppression of Twist1 expression resulted in decreased RLF accumulation due to increased apoptosis, whereas Twist1 overexpression protected RLFs against several apoptotic stimuli. Addition of platelet-derived growth factor in combination with other GFs led to an increase in proliferation. When Twist1 was depleted, GFs continued to act as mitogens but caused a marked increase in cell death. The increase in apoptosis under basal or growth factor-stimulated conditions was partly mediated by up-regulation of the proapoptotic Bcl-2 family members, Bim and PUMA. These findings indicate that Twist1 promotes survival and accumulation of fibroblasts by shaping their responsiveness to growth factor stimulation. We propose that Twist1 represents one of the factors that promotes pathogenic accumulation of fibroblasts in fibrotic lung disease.

Roles of P67/MetAP2 as a tumor suppressor

A precise balance between growth promoting signals and growth inhibitory signals plays important roles in the maintenance of healthy mammalian cells. Any deregulation of this critical balance converts normal cells into abnormal or cancerous cells. Several macromolecules are being identified and characterized that are involved in the regulation of cell signaling pathways that connect to the cell cycle and thus they play roles as tumor promoters or tumor suppressors. In situ tumor formation needs active angiogenesis, a process that generates new blood vessels from existing ones either by splitting or sprouting. Several small molecule inhibitors and proteins have been identified as inhibitors of angiogenesis. One such protein, p67/MetAP2 also known as methionine aminopeptidase 2 (MetAP2), has been shown to bind covalently to fumagillin and its derivatives that have anti-angiogenic activity. In addition to fumagillin or its derivatives, several other small molecule inhibitors of p67/MetAP2 have been recently identified and some of these drugs are in phase III trials for cancer therapy. Although molecular details of actions toward tumor suppression by these drugs are largely unknown, a significant progress has been made to understand the structure-function relationship of p67/MetAP2 and its roles in the maintenance of the levels of phosphorylation of the proportional, variant-subunit of eukaryotic initiation factor 2 (eIF2 proportional, variant) and extracellular signal-regulated kinases 1 and 2 (ERK1/2). In this article, roles of p67/MetAP2 in the suppression of cancer development are also discussed.