The Novel Small Molecule BTB Inhibits Pro-Fibrotic Fibroblast Behavior though Inhibition of RhoA Activity.

Idiopathic pulmonary fibrosis (IPF) is a progressive, chronic, interstitial lung disease with a poor prognosis. Although specific anti-fibrotic medications are now available, the median survival time following diagnosis remains very low, and new therapies are urgently needed. To uncover novel therapeutic targets, we examined how biochemical properties of the fibrotic lung are different from the healthy lung. Previous work identified lactate as a metabolite that is upregulated in IPF lung tissue. Importantly, inhibition of the enzyme responsible for lactate production prevents fibrosis in vivo. Further studies revealed that fibrotic lesions of the lung experience a significant decline in tissue pH, likely due to the overproduction of lactate. It is not entirely clear how cells in the lung respond to changes in extracellular pH, but a family of proton sensing G-protein coupled receptors has been shown to be activated by reductions in extracellular pH. This work examines the expression profiles of proton sensing GPCRs in non-fibrotic and IPF-derived primary human lung fibroblasts. We identify TDAG8 as a proton sensing GPCR that is upregulated in IPF fibroblasts and that knockdown of TDAG8 dampens myofibroblast differentiation. To our surprise, BTB, a proposed positive allosteric modulator of TDAG8, inhibits myofibroblast differentiation. Our data suggest that BTB does not require TDAG8 to inhibit myofibroblast differentiation, but rather inhibits myofibroblast differentiation through suppression of RhoA mediated signaling. Our work highlights the therapeutic potential of BTB as an anti-fibrotic treatment and expands upon the importance of RhoA-mediated signaling pathways in the context of myofibroblast differentiation. Furthermore, this works also suggests that TDAG8 inhibition may have therapeutic relevance in the treatment of IPF.

Ogerin mediated inhibition of TGF-ß(1) induced myofibroblast differentiation is potentiated by acidic pH.

Transforming growth factor beta (TGF-ß) induced myofibroblast differentiation is central to the pathological scarring observed in Idiopathic Pulmonary Fibrosis (IPF) and other fibrotic diseases. Our lab has recently identified expression of GPR68 (Ovarian Cancer Gene Receptor 1, OGR1), a pH sensing G-protein coupled receptor, as a negative regulator of TGF-ß induced profibrotic effects in primary human lung fibroblasts (PHLFs). We therefore hypothesized that small molecule activators of GPR68 would inhibit myofibroblast differentiation. Ogerin is a positive allosteric modulator (PAM) of GPR68, inducing a leftward shift of the dose response curve to proton induced signaling. Using PHLFs derived from patients with both non-fibrotic and IPF diagnoses, we show that Ogerin inhibits, and partially reverses TGF-ß induced myofibroblast differentiation in a dose dependent manner. This occurs at the transcriptional level without inhibition of canonical TGF-ß induced SMAD signaling. Ogerin induces PKA dependent CREB phosphorylation, a marker of Gαs pathway activation. The ability of Ogerin to inhibit both basal and TGF-ß induced collagen gene transcription, and induction of Gαs signaling is enhanced at an acidic pH (pH 6.8). Similar findings were also found using fibroblasts derived from dermal, intestinal, and orbital tissue. The biological role of GPR68 in different tissues, cell types, and disease states is an evolving and emerging field. This work adds to the understanding of Gαs coupled GPCRs in fibrotic lung disease, the ability to harness the pH sensing properties of GPR68, and conserved mechanisms of fibrosis across different organ systems.

The effect of air pollution on the transcriptomics of the immune response to respiratory infection.

Combustion related particulate matter air pollution (PM) is associated with an increased risk of respiratory infections in adults. The exact mechanism underlying this association has not been determined. We hypothesized that increased concentrations of combustion related PM would result in dysregulation of the innate immune system. This epidemiological study includes 111 adult patients hospitalized with respiratory infections who underwent transcriptional analysis of their peripheral blood. We examined the association between gene expression at the time of hospitalization and ambient measurements of particulate air pollutants in the 28 days prior to hospitalization. For each pollutant and time lag, gene-specific linear models adjusting for infection type were fit using LIMMA (Linear Models For Microarray Data), and pathway/gene set analyses were performed using the CAMERA (Correlation Adjusted Mean Rank) program. Comparing patients with viral and/or bacterial infection, the expression patterns associated with air pollution exposure differed. Adjusting for the type of infection, increased concentrations of Delta-C (a marker of biomass smoke) and other PM were associated with upregulation of iron homeostasis and protein folding. Increased concentrations of black carbon (BC) were associated with upregulation of viral related gene pathways and downregulation of pathways related to antigen presentation. The pollutant/pathway associations differed by lag time and by type of infection. This study suggests that the effect of air pollution on the pathogenesis of respiratory infection may be pollutant, timing, and infection specific.

The self-fulfilling prophecy of pulmonary fibrosis: a selective inspection of pathological signalling loops.

Pulmonary fibrosis is a devastating, progressive disease and carries a prognosis worse than most cancers. Despite ongoing research, the mechanisms that underlie disease pathogenesis remain only partially understood. However, the self-perpetuating nature of pulmonary fibrosis has led several researchers to propose the existence of pathological signalling loops. According to this hypothesis, the normal wound-healing process becomes corrupted and results in the progressive accumulation of scar tissue in the lung. In addition, several negative regulators of pulmonary fibrosis are downregulated and, therefore, are no longer capable of inhibiting these feed-forward loops. The combination of pathological signalling loops and loss of a checks and balances system ultimately culminates in a process of unregulated scar formation. This review details specific signalling pathways demonstrated to play a role in the pathogenesis of pulmonary fibrosis. The evidence of detrimental signalling loops is elucidated with regard to epithelial cell injury, cellular senescence and the activation of developmental and ageing pathways. We demonstrate where these loops intersect each other, as well as common mediators that may drive these responses and how the loss of pro-resolving mediators may contribute to the propagation of disease. By focusing on the overlapping signalling mediators among the many pro-fibrotic pathways, it is our hope that the pulmonary fibrosis community will be better equipped to design future trials that incorporate the redundant nature of these pathways as we move towards finding a cure for this unrelenting disease.

Caveolin-1 gene therapy inhibits inflammasome activation to protect from bleomycin-induced pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a devastating and fatal disease and characterized by increased deposition of extracellular matrix proteins and scar formation in the lung, resulting from alveolar epithelial damage and accumulation of inflammatory cells. Evidence suggests that Caveolin-1 (Cav-1), a major component of caveolae which regulates cell signaling and endocytosis, is a potential target to treat fibrotic diseases, although the mechanisms and responsible cell types are unclear. We show that Cav-1 expression was downregulated both in alveolar epithelial type I cells in bleomycin-injured mouse lungs and in lung sections from IPF patients. Increased expression of IL-1ß and caspase-1 has been observed in IPF patients, indicating inflammasome activation associated with IPF. Gene transfer of a plasmid expressing Cav-1 using transthoracic electroporation reduced infiltration of neutrophils and monocytes/macrophages and protected from subsequent bleomycin-induced pulmonary fibrosis. Overexpression of Cav-1 suppressed bleomycin- or silica-induced activation of caspase-1 and maturation of pro-IL-1ß to secrete cleaved IL-1ß both in mouse lungs and in primary type I cells. These results demonstrate that gene transfer of Cav-1 downregulates inflammasome activity and protects from subsequent bleomycin-mediated pulmonary fibrosis. This indicates a pivotal regulation of Cav-1 in inflammasome activity and suggests a novel therapeutic strategy for patients with IPF.

Reinterpreting Evidence of Rheumatoid Arthritis-Associated Interstitial Lung Disease to Understand Etiology.

Interstitial Lung Disease (ILD) is a well-known complication of rheumatoid arthritis (RA) which often results in significant morbidity and mortality. It is often diagnosed late in the disease process via descriptive criteria. Multiple subtypes of RA-ILD exist as defined by chest CT and histopathology. In the absence of formal natural history studies and definitive diagnostics, a conventional dogma has emerged that there are two major subtypes of RA-ILD (nonspecific interstitial pneumonia (NSIP) and Usual Interstitial Pneumonia (UIP)). These subtypes are based on clinical experience and correlation studies. However, recent animal model data are incongruous with established paradigms of RA-ILD and beg reassessment of the clinical evidence in order to better understand etiology, pathogenesis, prognosis, and response to therapy. To this end, here we: 1) review the literature on epidemiology, radiology, histopathology and clinical outcomes of the various RAILD subtypes, existing animal models, and current theories on RA-ILD pathogenesis; 2) highlight the major gaps in our knowledge; and 3) propose future research to test an emerging theory of RAILD that posits initial rheumatic lung inflammation in the form of NSIP-like pathology transforms mesenchymal cells to derive chimeric disease, and subsequently develops into frank UIP-like fibrosis in some RA patients. Elucidation of the pathogenesis of RA-ILD is critical for the development of effective interventions for RA-ILD.

The clinical impact of pneumocystis and viral PCR testing on bronchoalveolar lavage in immunosuppressed patients.

INTRODUCTION: Pulmonary infiltrates in immunosuppressed patients are common. Yields from bronchoscopy with bronchoalveolar lavage (BAL) has been reported to be between 31 and 65%. The clinical impact of pneumocystis and viral Polymerase chain reaction (PCR) testing on BAL has not been extensively evaluated in a mixed immunosuppressed patient population. METHODS: We performed a retrospective chart review of immunosuppressed adults with pulmonary infiltrates who underwent BAL at the University of Rochester Medical Center. Only one BAL per patient was included. We compared the rate of positive PCR testing to conventional testing. We then investigated factors associated with positive PCR testing. Finally, we assessed for changes in antimicrobial therapy after bronchoscopy. RESULTS: Three hundred and fifty-nine patients underwent BAL with 249 patients having pneumocystis PCR testing and 142 having viral PCR testing. Pneumocystis identification occurred in 43 patients and viral species identification occurred in 56 patients. PCR testing increased pneumocystis identification compared to microscopy, 14% vs. 5%, p = 0.01, and viral identification compared to culture, 25% vs. 6%, p = 0.0001. Of the patients with positive pneumocystis PCR testing 49% had antibiotics stopped, 66% were started on anti-pneumocystis therapy, and only 6% did not receive treatment. There was no difference in the number of patients with antibiotics stopped based on viral PCR testing results. DISCUSSION: PCR testing increases BAL yield in immunosuppressed patients compared to conventional testing. Pneumocystis identified by PCR only may cause a self-limited infection and may not require antimicrobial therapy. PCR testing should be included in the evaluation of pulmonary infiltrates in immunosuppressed patients.

Prevention and treatment of bleomycin-induced pulmonary fibrosis with the lactate dehydrogenase inhibitor gossypol.

Pulmonary fibrosis is a chronic and irreversible scarring disease in the lung with poor prognosis. Few therapies are available; therefore it is critical to identify new therapeutic targets. Our lab has previously identified the enzyme lactate dehydrogenase-A (LDHA) as a potential therapeutic target in pulmonary fibrosis. We found increases in LDHA protein and its metabolic product, lactate, in patients with idiopathic pulmonary fibrosis (IPF). Importantly, we described lactate as a novel pro-fibrotic mediator by acidifying the extracellular space, and activating latent transforming growth factor beta (TGF-ß1) in a pH-dependent manner. We propose a pro-fibrotic feed-forward loop by which LDHA produces lactate, lactate decreases pH in the extracellular space and activates TGF-ß1 which can further perpetuate fibrotic signaling. Our previous work also demonstrates that the LDHA inhibitor gossypol inhibits TGF-ß1-induced myofibroblast differentiation and collagen production in vitro. Here, we employed a mouse model of bleomycin-induced pulmonary fibrosis to test whether gossypol inhibits pulmonary fibrosis in vivo. We found that gossypol dose-dependently inhibits bleomycin-induced collagen accumulation and TGF-ß1 activation in mouse lungs when treatment is started on the same day as bleomycin administration. Importantly, gossypol was also effective at treating collagen accumulation when delayed 7 days following bleomycin. Our results demonstrate that inhibition of LDHA with the inhibitor gossypol is effective at both preventing and treating bleomycin-induced pulmonary fibrosis, and suggests that LDHA may be a potential therapeutic target for pulmonary fibrosis.

Development of an accurate and sensitive method for lactate analysis in exhaled breath condensate by LC MS/MS.

Exhaled breath condensate (EBC) is easily obtained for clinical diagnosis and prognosis for pulmonary diseases and has gained much interest in biomarker discovery research and studies. Lactate, a physiological material, is found in EBC and has been demonstrated to be a potential indicator of chronic obstructive pulmonary disease and other lung diseases. Several assays are available to detect lactate in human body fluids, and yet none is suitable for detecting lactate in EBC. Due to the very low concentration of lactate in EBC and low volume of EBC, it is very important to develop an assay to measure lactate with high sensitivity, accuracy and easy sample processing. We report here a novel LC-MS/MS based assay to measure lactate using HILIC column separation. Sample preparation was simple and straightforward through a "dilute and shoot" approach with a separation of 4min. The limit of quantification was determined to be 0.5µM. This assay was linear from 0.5µM to at least 100µM. The inter- and intra- day precision at the levels of 1µM, 10µM, and 100µM were less than 3% with recovery within 5.4% of expected values. There was no ion suppression for the assay, and no carry-over was observed up to 500µM. Furthermore, we discovered that lactate is ubiquitously present in the lab environment, which can create significant challenges for accurate detection of lactate at low concentrations. We provided practical approaches in this paper to overcome the challenges and ensure the accuracy of the assay. In summary, this article presents an accurate and sensitive method using LC-MS/MS for measuring lactate in EBC, and this method is suitable for measuring lactate concentrations for non-invasive monitoring of pulmonary functions.

The Lactate Dehydrogenase Inhibitor Gossypol Inhibits Radiation-Induced Pulmonary Fibrosis.

Exposure of the lung to ionizing radiation that occurs in radiotherapy, as well as after accidental or intentional mass casualty incident can result in pulmonary fibrosis, which has few treatment options. Pulmonary fibrosis is characterized by an accumulation of extracellular matrix proteins that create scar tissue. Although the mechanisms leading to radiation-induced pulmonary fibrosis remain poorly understood, one frequent observation is the activation of the profibrotic cytokine transforming growth factor-beta (TGF-ß). Our laboratory has shown that the metabolite lactate activates latent TGF-ß by a reduction in extracellular pH. We recently demonstrated that lactate dehydrogenase-A (LDHA), the enzyme that produces lactate, is upregulated in patients with radiation-induced pulmonary fibrosis. Furthermore, genetic silencing of LDHA or pharmacologic inhibition using the LDHA inhibitor gossypol prevented radiation-induced extracellular matrix secretion in vitro through inhibition of TGF-ß activation. In the current study, we hypothesized that LDHA inhibition in vivo prevents radiation-induced pulmonary fibrosis. To test this hypothesis, C57BL/6 mice received 5 Gy total-body irradiation plus 10 Gy thoracic irradiation from a 137Cs source to induce pulmonary fibrosis. Starting at 4 weeks postirradiation, mice were treated with 5 mg/kg of the LDHA inhibitor gossypol or vehicle daily until sacrifice at 26 weeks postirradiation. Exposure to radiation resulted in pulmonary fibrosis, characterized by an increase in collagen content, fibrosis area, extracellular matrix gene expression and TGF-ß activation. Irradiated mice treated with gossypol had significantly reduced fibrosis outcomes, including reduced collagen content in the lungs, reduced expression of active TGF-ß, LDHA and the transcription factor hypoxia-inducible factor-1 alpha (HIF-1α). These findings suggest that inhibition of LDHA protects against radiation-induced pulmonary fibrosis, and may be a novel therapeutic strategy for radiation-induced pulmonary fibrosis.

Alternative Progenitor Lineages Regenerate the Adult Lung Depleted of Alveolar Epithelial Type 2 Cells.

An aberrant oxygen environment at birth increases the severity of respiratory viral infections later in life through poorly understood mechanisms. Here, we show that alveolar epithelial cell (AEC) 2 cells (AEC2s), progenitors for AEC1 cells, are depleted in adult mice exposed to neonatal hypoxia or hyperoxia. Airway cells expressing surfactant protein (SP)-C and ATP binding cassette subfamily A member 3, alveolar pod cells expressing keratin (KRT) 5, and pulmonary fibrosis were observed when these mice were infected with a sublethal dose of HKx31, H3N2 influenza A virus. This was not seen in infected siblings birthed into room air. Genetic lineage tracing studies in mice exposed to neonatal hypoxia or hyperoxia revealed pre-existing secretoglobin 1a1+ cells produced airway cells expressing SP-C and ATP binding cassette subfamily A member 3. Pre-existing Kr5+ progenitor cells produced squamous alveolar cells expressing receptor for advanced glycation endproducts, aquaporin 5, and T1α in alveoli devoid of AEC2s. They were not the source of KRT5+ alveolar pod cells. These oxygen-dependent changes in epithelial cell regeneration and fibrosis could be recapitulated by conditionally depleting AEC2s in mice using diphtheria A toxin and then infecting with influenza A virus. Likewise, airway cells expressing SP-C and alveolar cells expressing KRT5 were observed in human idiopathic pulmonary fibrosis. These findings suggest that alternative progenitor lineages are mobilized to regenerate the alveolar epithelium when AEC2s are severely injured or depleted by previous insults, such as an adverse oxygen environment at birth. Because these lineages regenerate AECs in spatially distinct compartments of a lung undergoing fibrosis, they may not be sufficient to prevent disease.

The Global Genome Biodiversity Network (GGBN) Data Standard specification.

Genomic samples of non-model organisms are becoming increasingly important in a broad range of studies from developmental biology, biodiversity analyses, to conservation. Genomic sample definition, description, quality, voucher information and metadata all need to be digitized and disseminated across scientific communities. This information needs to be concise and consistent in today's ever-increasing bioinformatic era, for complementary data aggregators to easily map databases to one another. In order to facilitate exchange of information on genomic samples and their derived data, the Global Genome Biodiversity Network (GGBN) Data Standard is intended to provide a platform based on a documented agreement to promote the efficient sharing and usage of genomic sample material and associated specimen information in a consistent way. The new data standard presented here build upon existing standards commonly used within the community extending them with the capability to exchange data on tissue, environmental and DNA sample as well as sequences. The GGBN Data Standard will reveal and democratize the hidden contents of biodiversity biobanks, for the convenience of everyone in the wider biobanking community. Technical tools exist for data providers to easily map their databases to the standard.Database URL: http://terms.tdwg.org/wiki/GGBN_Data_Standard.

Normal Human Lung Epithelial Cells Inhibit Transforming Growth Factor-ß Induced Myofibroblast Differentiation via Prostaglandin E2.

INTRODUCTION: Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disease with very few effective treatments. The key effector cells in fibrosis are believed to be fibroblasts, which differentiate to a contractile myofibroblast phenotype with enhanced capacity to proliferate and produce extracellular matrix. The role of the lung epithelium in fibrosis is unclear. While there is evidence that the epithelium is disrupted in IPF, it is not known whether this is a cause or a result of the fibroblast pathology. We hypothesized that healthy epithelial cells are required to maintain normal lung homeostasis and can inhibit the activation and differentiation of lung fibroblasts to the myofibroblast phenotype. To investigate this hypothesis, we employed a novel co-culture model with primary human lung epithelial cells and fibroblasts to investigate whether epithelial cells inhibit myofibroblast differentiation. MEASUREMENTS AND MAIN RESULTS: In the presence of transforming growth factor (TGF)-ß, fibroblasts co-cultured with epithelial cells expressed significantly less α-smooth muscle actin and collagen and showed marked reduction in cell migration, collagen gel contraction, and cell proliferation compared to fibroblasts grown without epithelial cells. Epithelial cells from non-matching tissue origins were capable of inhibiting TGF-ß induced myofibroblast differentiation in lung, keloid and Graves' orbital fibroblasts. TGF-ß promoted production of prostaglandin (PG) E2 in lung epithelial cells, and a PGE2 neutralizing antibody blocked the protective effect of epithelial cell co-culture. CONCLUSIONS: We provide the first direct experimental evidence that lung epithelial cells inhibit TGF-ß induced myofibroblast differentiation and pro-fibrotic phenotypes in fibroblasts. This effect is not restricted by tissue origin, and is mediated, at least in part, by PGE2. Our data support the hypothesis that the epithelium plays a crucial role in maintaining lung homeostasis, and that damaged and/ or dysfunctional epithelium contributes to the development of fibrosis.

Ionizing radiation induces myofibroblast differentiation via lactate dehydrogenase.

Pulmonary fibrosis is a common and dose-limiting side-effect of ionizing radiation used to treat cancers of the thoracic region. Few effective therapies are available for this disease. Pulmonary fibrosis is characterized by an accumulation of myofibroblasts and excess deposition of extracellular matrix proteins. Although prior studies have reported that ionizing radiation induces fibroblast to myofibroblast differentiation and collagen production, the mechanism remains unclear. Transforming growth factor-ß (TGF-ß) is a key profibrotic cytokine that drives myofibroblast differentiation and extracellular matrix production. However, its activation and precise role in radiation-induced fibrosis are poorly understood. Recently, we reported that lactate activates latent TGF-ß through a pH-dependent mechanism. Here, we wanted to test the hypothesis that ionizing radiation leads to excessive lactate production via expression of the enzyme lactate dehydrogenase-A (LDHA) to promote myofibroblast differentiation. We found that LDHA expression is increased in human and animal lung tissue exposed to ionizing radiation. We demonstrate that ionizing radiation induces LDHA, lactate production, and extracellular acidification in primary human lung fibroblasts in a dose-dependent manner. We also demonstrate that genetic and pharmacologic inhibition of LDHA protects against radiation-induced myofibroblast differentiation. Furthermore, LDHA inhibition protects from radiation-induced activation of TGF-ß. We propose a profibrotic feed forward loop, in which radiation induces LDHA expression and lactate production, which can lead to further activation of TGF-ß to drive the fibrotic process. These studies support the concept of LDHA as an important therapeutic target in radiation-induced pulmonary fibrosis.

Resolvins attenuate inflammation and promote resolution in cigarette smoke-exposed human macrophages.

Inflammation is a protective response to injury, but it can become chronic, leading to tissue damage and disease. Cigarette smoke causes multiple inflammatory diseases, which account for thousands of deaths and cost billions of dollars annually. Cigarette smoke disrupts the function of immune cells, such as macrophages, by prolonging inflammatory signaling, promoting oxidative stress, and impairing phagocytosis, contributing to increased incidence of infections. Recently, new families of lipid-derived mediators, "specialized proresolving mediators" (SPMs), were identified. SPMs play a critical role in the active resolution of inflammation by counterregulating proinflammatory signaling and promoting resolution pathways. We have identified dysregulated concentrations of lipid mediators in exhaled breath condensate, bronchoalveolar lavage fluid, and serum from patients with chronic obstructive pulmonary disease (COPD). In human alveolar macrophages from COPD and non-COPD patients, D-series resolvins decreased inflammatory cytokines and enhanced phagocytosis. To further investigate the actions of resolvins on human cells, macrophages were differentiated from human blood monocytes and treated with D-series resolvins and then exposed to cigarette smoke extract. Resolvins significantly suppressed macrophage production of proinflammatory cytokines, enzymes, and lipid mediators. Resolvins also increased anti-inflammatory cytokines, promoted an M2 macrophage phenotype, and restored cigarette smoke-induced defects in phagocytosis, highlighting the proresolving functions of these molecules. These actions were receptor-dependent and involved modulation of canonical and noncanonical NF-κB expression, with the first evidence for SPM action on alternative NF-κB signaling. These data show that resolvins act on human macrophages to attenuate cigarette smoke-induced inflammatory effects through proresolving mechanisms and provide new evidence of the therapeutic potential of SPMs.

Inhibition of transglutaminase 2, a novel target for pulmonary fibrosis, by two small electrophilic molecules.

Idiopathic pulmonary fibrosis (IPF) is characterized by progressive fibrotic destruction of normal lung architecture. Due to a lack of effective treatment options, new treatment approaches are needed. We previously identified transglutaminase (TG)2, a multifunctional protein expressed by human lung fibroblasts (HLFs), as a positive driver of fibrosis. TG2 catalyzes crosslinking of extracellular matrix proteins, enhances cell binding to fibronectin and integrin, and promotes fibronectin expression. We investigated whether the small electrophilic molecules 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO) and 15-deoxy-delta-12,14-prostaglandin J2 (15d-PGJ2) inhibit the expression and profibrotic functions of TG2. CDDO and 15d-PGJ2 reduced expression of TG2 mRNA and protein in primary HLFs from control donors and donors with IPF. CDDO and 15d-PGJ2 also decreased the in vitro profibrotic effector functions of HLFs including collagen gel contraction and cell migration. The decrease in TG2 expression did not occur through activation of the peroxisome proliferator activated receptor γ or generation of reactive oxidative species. CDDO and 15d-PGJ2 inhibited the extracellular signal-regulated kinase pathway, resulting in the suppression of TG2 expression. This is the first study to show that small electrophilic compounds inhibit the expression and profibrotic effector functions of TG2, a key promoter of fibrosis. These studies identify new and important antifibrotic activities of these two small molecules, which could lead to new treatments for fibrotic lung disease.

Spiruchostatin A inhibits proliferation and differentiation of fibroblasts from patients with pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a progressive scarring disorder characterized by the proliferation of interstitial fibroblasts and the deposition of extracellular matrix causing impaired gas exchange. Spiruchostatin A (SpA) is a histone deacetylase inhibitor (HDI) with selectivity toward Class I enzymes, which distinguishes it from other nonspecific HDIs that are reported to inhibit (myo)fibroblast proliferation and differentiation. Because the selectivity of HDIs may be important clinically, we postulated that SpA inhibits the proliferation and differentiation of IPF fibroblasts. Primary fibroblasts were grown from lung biopsy explants obtained from patients with IPF or from normal control subjects, using two-dimensional or three-dimensional culture models. The effect of SpA on fibroproliferation in serum-containing medium ± transforming growth factor (TGF)-ß(1) was quantified by methylene blue binding. The acetylation of histone H3, the expression of the cell-cycle inhibitor p21(waf1), and the myofibroblast markers α-smooth muscle actin (α-SMA) and collagens I and III were determined by Western blotting, quantitative RT-PCR, immunofluorescent staining, or colorimetry. SpA inhibited the proliferation of IPF or normal fibroblasts in a time-dependent and concentration-dependent manner (concentration required to achieve 50% inhibition = 3.8 ± 0.4 nM versus 7.8 ± 0.2 nM, respectively; P < 0.05), with little cytotoxicity. Western blot analyses revealed that SpA caused a concentration-dependent increase in histone H3 acetylation, paralleling its antiproliferative effect. SpA also increased p21(waf1) expression, suggesting that direct cell-cycle regulation was the mechanism of inhibiting proliferation. Although treatment with TGF-ß(1) induced myofibroblast differentiation associated with increased expression of α-SMA, collagen I and collagen III and soluble collagen release, these responses were potently inhibited by SpA. These data support the concept that bicyclic tetrapeptide HDIs merit further investigation as potential treatments for IPF.

Transglutaminase 2 and its role in pulmonary fibrosis.

RATIONALE: Idiopathic pulmonary fibrosis (IPF) is a deadly progressive disease with few treatment options. Transglutaminase 2 (TG2) is a multifunctional protein, but its function in pulmonary fibrosis is unknown. OBJECTIVES: To determine the role of TG2 in pulmonary fibrosis. METHODS: The fibrotic response to bleomycin was compared between wild-type and TG2 knockout mice. Transglutaminase and transglutaminase-catalyzed isopeptide bond expression was examined in formalin-fixed human lung biopsy sections by immunohistochemistry from patients with IPF. In addition, primary human lung fibroblasts were used to study TG2 function in vitro. MEASUREMENTS AND MAIN RESULTS: TG2 knockout mice developed significantly reduced fibrosis compared with wild-type mice as determined by hydroxyproline content and histologic fibrosis score (P < 0.05). TG2 expression and activity are increased in lung biopsy sections in humans with IPF compared with normal control subjects. In vitro overexpression of TG2 led to increased fibronectin deposition, whereas transglutaminase knockdown led to defects in contraction and adhesion. The profibrotic cytokine transforming growth factor-ß causes an increase in membrane-localized TG2, increasing its enzymatic activity. CONCLUSIONS: TG2 is involved in pulmonary fibrosis in a mouse model and in human disease and is important in normal fibroblast function. With continued research on TG2, it may offer a new therapeutic target.

Peroxisome proliferator-activated receptor-gamma ligands induce heme oxygenase-1 in lung fibroblasts by a PPARgamma-independent, glutathione-dependent mechanism.

Oxidative stress plays an important role in the pathogenesis of pulmonary fibrosis. Heme oxygenase-1 (HO-1) is a key antioxidant enzyme, and overexpression of HO-1 significantly decreases lung inflammation and fibrosis in animal models. Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a transcription factor that regulates adipogenesis, insulin sensitization, and inflammation. We report here that the PPARgamma ligands 15d-PGJ2 and 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO), which have potent antifibrotic effects in vitro, also strongly induce HO-1 expression in primary human lung fibroblasts. Pharmacological and genetic approaches are used to demonstrate that induction of HO-1 is PPARgamma independent. Upregulation of HO-1 coincides with decreased intracellular glutathione (GSH) levels and can be inhibited by N-acetyl cysteine (NAC), a thiol antioxidant and GSH precursor. Upregulation of HO-1 is not inhibited by Trolox, a non-thiol antioxidant, and does not involve the transcription factors AP-1 or Nrf2. CDDO and 15d-PGJ2 contain an alpha/beta unsaturated ketone that acts as an electrophilic center that can form covalent bonds with free reduced thiols. Rosiglitazone, a PPARgamma ligand that lacks an electrophilic center, does not induce HO-1. These data suggest that in human lung fibroblasts, 15d-PGJ2 and CDDO induce HO-1 via a GSH-dependent mechanism involving the formation of covalent bonds between 15d-PGJ2 or CDDO and GSH. Inhibiting HO-1 upregulation with NAC has only a small effect on the antifibrotic properties of 15d-PGJ2 and CDDO in vitro. These results suggest that CDDO and similar electrophilic PPARgamma ligands may have great clinical potential as antifibrotic agents, not only through direct effects on fibroblast differentiation and function, but indirectly by bolstering antioxidant defenses.