Cluster analysis identifies novel real-world lung disease-pulmonary hypertension subphenotypes: implications for treatment response

Background

Clinical trials repurposing pulmonary arterial hypertension (PAH) therapies to patients with lung disease- or hypoxia-pulmonary hypertension (PH) (classified as World Health Organization Group 3 PH) have failed to show a consistent benefit. However, Group 3 PH clinical heterogeneity suggests robust phenotyping may inform detection of treatment-responsive subgroups. We hypothesised that cluster analysis would identify subphenotypes with differential responses to oral PAH therapy.

Methods

Two k-means analyses were performed on a national cohort of US veterans with Group 3 PH; an inclusive model (I) of all treated patients (n=196) and a haemodynamic model (H) limited to patients with right heart catheterisations (n=112). The primary outcome was organ failure or all-cause mortality by cluster. An exploratory analysis evaluated within-cluster treatment effects.

Results

Three distinct clusters of Group 3 PH patients were identified. In the inclusive model (C1I n=43, 21.9%; C2I n=102, 52.0%; C3I n=51, 26.0%), lung disease and spirometry drove cluster assignment. By contrast, in the haemodynamic model (C1H n=44, 39.3%; C2H n=43, 38.4%; C3H n=25, 22.3%), right heart catheterisation data surpassed the importance of lung disease and spirometry. In the haemodynamic model, compared to C3H, C1H experienced the greatest hazard for respiratory failure or death (HR 6.1, 95% CI 3.2-11.8). In an exploratory analysis, cluster determined treatment response (p=0.006). Conclusions regarding within-cluster treatment responses were limited by significant differences between select variables in the treated and untreated groups.

Conclusions

Cluster analysis identifies novel real-world subphenotypes of Group 3 PH patients with distinct clinical trajectories. Future studies may consider this methodological approach to identify subgroups of heterogeneous patients that may be responsive to existing pulmonary vasodilatory therapies.

Real-world use of inhaled treprostinil for lung disease-pulmonary hypertension: A protocol for patient evaluation and prescribing

Inhaled treprostinil was approved recently for interstitial lung disease-pulmonary hypertension; however, efficacy in "real-world" populations is not known. We designed a protocol and report our experience evaluating 10 patients referred for therapy. Misdiagnosis at presentation was common; ultimately, three patients (30%) were prescribed drug. This protocol offers an opportunity to standardize longitudinal assessment of inhaled treprostinil in clinical practice.

Tadalafil for veterans with chronic obstructive pulmonary disease-pulmonary hypertension: A multicenter, placebo-controlled randomized trial

Treating Veterans with chronic obstructive pulmonary disease complicated by pulmonary hypertension (COPD-PH) using phosphodiesterase type-5 inhibitor pharmacotherapy is common, but efficacy data are lacking. To address this further, patients with COPD-PH from five Department of Veterans Affairs hospitals were randomized (1∶1) to receive placebo or oral tadalafil (40 mg/day) for 12 months. The primary endpoint was changed from baseline in 6-min walk distance at 12 months. Secondary endpoints included change from baseline in pulmonary vascular resistance, mean pulmonary artery pressure, and symptom burden by the University of California San Diego shortness of breath questionnaire scale at 6 months. A total of 42 subjects (all male; 68 ± 7.6 years old) were randomized to placebo (N = 14) or tadalafil (N = 28). The group imbalance was related to under-enrollment. Compared to placebo, no significant difference was observed in the tadalafil group for change from the primary endpoint or change in mean pulmonary artery pressure or pulmonary vascular resistance from baseline at 6 months. A clinically meaningful improvement was observed in the secondary endpoint of shortness of breath questionnaire score in the tadalafil versus placebo group at 6 months. There was no significant difference in major adverse events between treatment groups, and tadalafil was well tolerated overall. For Veterans with COPD-PH enrolled in this study, once-daily treatment with tadalafil did not improve 6-min walk distance or cardiopulmonary hemodynamics although a decrease in shortness of breath was observed. Under-enrollment and imbalanced randomization confound interpreting conclusions from this clinical trial and limit the generalization of our findings.

Pulmonary vascular resistance and clinical outcomes in patients with pulmonary hypertension: a retrospective cohort study

BACKGROUND

In pulmonary hypertension subgroups, elevated pulmonary vascular resistance (PVR) of 3·0 Wood units or more is associated with poor prognosis. However, the spectrum of PVR risk in pulmonary hypertension is not known. To address this area of uncertainty, we aimed to analyse the relationship between PVR and adverse clinical outcomes in pulmonary hypertension.

METHODS

We did a retrospective cohort study of all patients undergoing right heart catheterisation (RHC) in the US Veterans Affairs health-care system (Oct 1, 2007-Sep 30, 2016). Patients were included in the analyses if data from a complete RHC and at least 1 year of follow-up were available. Both inpatients and outpatients were included, but individuals with missing mean pulmonary artery pressure (mPAP), pulmonary artery wedge pressure, or cardiac output were excluded. The primary outcome measure was time to all-cause mortality assessed by the Veteran Affairs vital status file. Cox proportional hazards models were used to assess the association between PVR and outcomes, and the mortality hazard ratio was validated in a RHC cohort from Vanderbilt University Medical Center (Sept 24, 1998-June 1, 2016).

FINDINGS

The primary cohort (N=40 082; 38 751 [96·7%] male; median age 66·5 years [IQR 61·1-73·5]; median follow-up 1153 days [IQR 570-1971]), included patients with a history of heart failure (23 201 [57·9%]) and chronic obstructive pulmonary disease (13 348 [33·3%]). We focused on patients at risk for pulmonary hypertension based on a mPAP of at least 19 mm Hg (32 725 [81·6%] of 40 082). When modelled as a continuous variable, the all-cause mortality hazard for PVR was increased at around 2·2 Wood units compared with PVR of 1·0 Wood unit. Among patients with a mPAP of at least 19 mm Hg and pulmonary artery wedge pressure of 15 mm Hg or less, the adjusted hazard ratio (HR) for mortality was 1·71 (95% CI 1·59-1·84; p<0·0001) and for heart failure hospitalisation was 1·27 (1·13-1·43; p=0·0001), when comparing PVR of 2·2 Wood units or more to less than 2·2 Wood units. The validation cohort (N=3699, 1860 [50·3%] male, median age 60·4 years [49·5-69·2]; median follow-up 1752 days [IQR 1281-2999]) included 2870 patients [77·6%] with mPAP of at least 19 mm Hg (1418 [49·4%] male). The adjusted mortality HR for patients in the mPAP of 19 mm Hg or more group and with PVR of 2·2 Wood units or more and pulmonary artery wedge pressure of 15 mm or less Hg (1221 [42·5%] of 2870) was 1·81 (95% CI 1·33-2·47; p=0·0002).

INTERPRETATION

These data widen the continuum of clinical risk for mortality and heart failure in patients referred for RHC with elevated pulmonary artery pressure to include PVR of around 2.2 Wood units and higher. Testing the generalisability of these findings in at-risk populations with fewer cardiopulmonary comorbidities is warranted.

FUNDING

None.

Association of Borderline Pulmonary Hypertension With Mortality and Hospitalization in a Large Patient Cohort: Insights From the Veterans Affairs Clinical Assessment, Reporting, and Tracking Program

BACKGROUND

Pulmonary hypertension (PH) is associated with increased morbidity across the cardiopulmonary disease spectrum. Based primarily on expert consensus opinion, PH is defined by a mean pulmonary artery pressure (mPAP) ≥25 mm Hg. Although mPAP levels below this threshold are common among populations at risk for PH, the relevance of mPAP <25 mm Hg to clinical outcome is unknown.

METHODS AND RESULTS

We analyzed retrospectively all US veterans undergoing right heart catheterization (2007-2012) in the Veterans Affairs healthcare system (n=21,727; 908-day median follow-up). Cox proportional hazards models were used to evaluate the association between mPAP and outcomes of all-cause mortality and hospitalization, adjusted for clinical covariates. When treating mPAP as a continuous variable, the mortality hazard increased beginning at 19 mm Hg (hazard ratio [HR]=1.183; 95% confidence interval [CI], 1.004-1.393) relative to 10 mm Hg. Therefore, patients were stratified into 3 groups: (1) referent (≤18 mm Hg; n=4,207); (2) borderline PH (19-24 mm Hg; n=5,030); and (3) PH (≥25 mm Hg; n=12,490). The adjusted mortality hazard was increased for borderline PH (HR=1.23; 95% CI, 1.12-1.36; P<0.0001) and PH (HR=2.16; 95% CI, 1.96-2.38; P<0.0001) compared with the referent group. The adjusted hazard for hospitalization was also increased in borderline PH (HR=1.07; 95% CI, 1.01-1.12; P=0.0149) and PH (HR=1.15; 95% CI, 1.09-1.22; P<0.0001). The borderline PH cohort remained at increased risk for mortality after excluding the following high-risk subgroups: (1) patients with pulmonary artery wedge pressure >15 mm Hg; (2) pulmonary vascular resistance ≥3.0 Wood units; or (3) inpatient status at the time of right heart catheterization.

CONCLUSIONS

These data illustrate a continuum of risk according to mPAP level and that borderline PH is associated with increased mortality and hospitalization. Future investigations are needed to test the generalizability of our findings to other populations and study the effect of treatment on outcome in borderline PH.

Protocol for exercise hemodynamic assessment: performing an invasive cardiopulmonary exercise test in clinical practice

Invasive cardiopulmonary exercise testing (iCPET) combines full central hemodynamic assessment with continuous measurements of pulmonary gas exchange and ventilation to help in understanding the pathophysiology underpinning unexplained exertional intolerance. There is increasing evidence to support the use of iCPET as a key methodology for diagnosing heart failure with preserved ejection fraction and exercise-induced pulmonary hypertension as occult causes of exercise limitation, but there is little information available outlining the methodology to use this diagnostic test in clinical practice. To bridge this knowledge gap, the operational protocol for iCPET at our institution is discussed in detail. In turn, a standardized iCPET protocol may provide a common framework to describe the evolving understanding of mechanism(s) that limit exercise capacity and to facilitate research efforts to define novel treatments in these patients.

Study design and rationale for investigating phosphodiesterase type 5 inhibition for the treatment of pulmonary hypertension due to chronic obstructive lung disease: the TADA-PHiLD (TADAlafil for Pulmonary Hypertension associated with chronic obstructive Lung Disease) trial

In patients with chronic obstructive pulmonary disease (COPD), moderate or severe pulmonary hypertension (COPD-PH) is associated with increased rates of morbidity and mortality. Despite this, approaches to treatment and the efficacy of phosphodiesterase type 5 inhibition (PDE-5i) in COPD-PH are unresolved. We present the clinical rationale and study design to assess the effect of oral tadalafil on exercise capacity, cardiopulmonary hemodynamics, and clinical outcome measures in COPD-PH patients. Male and female patients 40-85 years old with GOLD stage 2 COPD or higher and pulmonary hypertension diagnosed on the basis of invasive cardiac hemodynamic assessment (mean pulmonary artery pressure [mPAP] >30 mmHg, pulmonary vascular resistance [PVR] >2.5 Wood units, and pulmonary capillary wedge pressure ≤18 mmHg at rest) will be randomized at a 1∶1 ratio to receive placebo or oral PDE-5i with tadalafil (40 mg daily for 12 months). The primary end point is change from baseline in 6-minute walk distance at 12 months. The secondary end points are change from baseline in PVR and mPAP at 6 months and change from baseline in peak volume of oxygen consumption ([Formula: see text]) during exercise at 12 months. Changes in systemic blood pressure and/or oxyhemoglobin saturation (Sao2) at rest and during exercise will function as safety outcome measures. TADA-PHiLD (TADAlafil for Pulmonary Hypertension assocIated with chronic obstructive Lung Disease) is the first sufficiently powered randomized clinical trial testing the effect of PDE-5i on key clinical and drug safety outcome measures in patients with at least moderate PH due to COPD.

Cellular FLICE-like inhibitory protein deviates myofibroblast fas-induced apoptosis toward proliferation during lung fibrosis

A prominent feature of fibrotic tissue in general and of lungs in particular is fibroblast proliferation and accumulation. In patients overcoming fibrosis, apoptosis limits this excessive cell growth. We have previously shown resistance to Fas-induced apoptosis of primary lung fibroblasts from mice with bleomycin-induced lung fibrosis, their escape from immune surveillance, and continued accumulation in spite of overexpression of the Fas death receptor. Cellular FLICE-like inhibitory protein (c-FLIP) is a regulator of cell death receptor-induced apoptosis in many cell types. We aimed to determine c-FLIP levels in myofibroblasts from fibrotic lungs and to directly assess c-FLIP's role in apoptosis and proliferation of primary lung myofibroblasts. c-FLIP levels were determined by apoptosis gene array, flow cytometry, Western blot, and immunofluorescence before and after down-regulation with a specific small interfering RNA. Apoptosis was assessed by caspase cleavage in Western blot and by Annexin V affinity labeling after FACS and tissue immunofluorescence. Proliferation was assessed by BrdU uptake, also using FACS and immunofluorescence. We show that myofibroblasts from lungs of humans with idiopathic pulmonary fibrosis and from bleomycin-treated versus normal saline-treated mice up-regulate c-FLIP levels. Using the animal model, we show that fibrotic lung myofibroblasts divert Fas signaling from apoptosis to proliferation and that this requires signaling by TNF receptor-associated factor (TRAF) and NF-κB. c-FLIP down-regulation reverses the effect of Fas activation, causing increased apoptosis, decreased proliferation, and diminished recruitment of TRAF to the DISC complex. This indicates that c-FLIP is essential for myofibroblast accumulation and may serve as a potential target to manipulate tissue fibrosis.

Transcriptional changes associated with recovery from heart failure in the SHR

To identify biological pathways associated with myocardial recovery from heart failure (HF), gene profiling and gene set enrichment analysis (GSEA) were examined in left ventricle of spontaneously hypertensive rats with HF (SHR-F) with no treatment, following treatment with the angiotensin converting enzyme inhibitor captopril, and treatment with captopril combined with the short chain fatty acid derivative phenylbutyrate. Failing hearts demonstrated depressed left ventricular ejection fraction, while ventricular volume and mass increased. Captopril treatment alone prevented further deterioration but did not improve myocardial function; relatively few transcripts were differentially expressed relative to untreated SHR-F. Gene sets identified by GSEA as downregulated with captopril treatment compared to SHR-F group included those related to hypoxia and reactive oxygen species, while upregulated gene sets included G protein signaling. Treatment with phenylbutyrate alone did not improve survival (no animals in this group survived the 30 day treatment period), while phenylbutyrate combined with captopril increased survival and significantly improved cardiac function in vivo and in vitro. Normalized microarray data identified 780 genes that demonstrated a combined treatment effect of which 258 genes were modified with HF. Fatty acid metabolism and ion transport were among the most significantly upregulated pathways in the combined treatment group compared to untreated SHR with HF, whereas those related to oxidative stress, growth, inflammation, protein degradation, and TGF-beta signaling were downregulated. These findings demonstrate improved myocardial function and regression of cardiac hypertrophy, and identify many HF related gene sets altered with phenylbutyrate and captopril treatment, but not captopril alone. These results characterize gene sets associated with recovery from HF, and suggest that phenylbutyrate may be a potentially effective adjunctive treatment, together with captopril, by synergistically modulating pathways that contribute to restoration of contractile function of the failing SHR heart.

Transition from compensated hypertrophy to systolic heart failure in the spontaneously hypertensive rat: Structure, function, and transcript analysis

Gene expression, determined by micro-array analysis, and left ventricular (LV) remodeling associated with the transition to systolic heart failure (HF) were examined in the spontaneously hypertensive rat (SHR). By combining transcript and gene set enrichment analysis (GSEA) of the LV with assessment of function and structure in age-matched SHR with and without HF, we aimed to better understand the molecular events underlying the onset of hypertensive HF. Failing hearts demonstrated depressed LV ejection fraction, systolic blood pressure, and LV papillary muscle force while LV end-diastolic and systolic volume and ventricular mass increased. 1431 transcripts were differentially expressed between failing and non-failing animals. GSEA identified multiple enriched gene sets, including those involving inflammation, oxidative stress, cell degradation and cell death, as well as TGF-beta and insulin signaling pathways. Our findings support the concept that these pathways and mechanisms may contribute to deterioration of cardiac function and remodeling associated with hypertensive HF.

Precipitation of low-temperature dolomite from an anaerobic microbial consortium: the role of methanogenic Archaea

Here we report precipitation of dolomite at low temperature (30 degrees C) mediated by a mixed anaerobic microbial consortium composed of dissimilatory iron-reducing bacteria (DIRB), fermenters, and methanogens. Initial solution geochemistry is controlled by DIRB, but after 90 days shifts to a system dominated by methanogens. In live experiments conditions are initially saturated with respect to dolomite (Omega(dol) = 19.40) and increase by two orders of magnitude (Omega(dol) = 2 330.77) only after the onset of methanogenesis, as judged by the increasing [CH(4)] and the detection of methanogenic micro-organisms. We identify ordered dolomite in live microcosms after 90 days via powder X-ray diffraction, while sterile controls precipitate only calcite. Scanning electron microscopy and transmitted electron microscopy demonstrate that the precipitated dolomite is closely associated with cell walls and putative extra-cellular polysaccharides. Headspace gas measurements and denaturing gradient gel electrophoresis confirm the presence of both autotrophic and acetoclastic methanogens and exclude the presence of DIRB and sulfate-reducing bacteria after dolomite begins forming. Furthermore, the absence of dolomite in the controls and prior to methanogenesis confirm that methanogenic Archaea are necessary for the low-temperature precipitation of dolomite under the experimental conditions tested.

Activation of elastin transcription by transforming growth factor-beta in human lung fibroblasts

Elastin synthesis is essential for lung development and postnatal maturation as well as for repair following injury. Using human embryonic lung fibroblasts that express undetectable levels of elastin as assessed by Northern analyses, we found that treatment with exogenous transforming growth factor-beta (TGF-beta) induced rapid and transient increases in levels of elastin heterogeneous nuclear RNA (hnRNA) followed by increases of elastin mRNA and protein expression. In fibroblasts derived from transgenic mice, TGF-beta induced increases in the expression of a human elastin gene promoter fragment driving a chloramphenicol acetyl transferase reporter gene. The induction of elastin hnRNA and mRNA expression by TGF-beta was abolished by pretreatments with TGF-beta receptor I inhibitor, global transcription inhibitor actinomycin D, and partially blocked by addition of protein synthesis inhibitor cycloheximide, but was not affected by the p44/42 MAPK inhibitor U0126. Pretreatment with the p38 MAPK inhibitor SB-203580 also partially attenuated the levels of TGF-beta-induced elastin mRNA but not its hnRNA. Western analysis indicated that TGF-beta stimulated Akt phosphorylation. Inhibition of phosphatidylinositol 3-kinase and Akt phosphorylation by LY-294002 abolished TGF-beta-induced increases in elastin hnRNA and mRNA expression. Treatment of lung fibroblasts with interleukin-1beta or the histone deacetylase inhibitor trichostatin A inhibited TGF-beta-induced elastin mRNA and hnRNA expression by a mechanism that involved inhibition of Akt phosphorylation. Downregulation of Akt2 but not Akt1 expression employing small interfering RNA duplexes blocked TGF-beta-induced increases of elastin hnRNA and mRNA levels. Together, our results demonstrated that TGF-beta activates elastin transcription that is dependent on phosphatidylinositol 3-kinase/Akt activity.

Fibulin-5 gene expression in human lung fibroblasts is regulated by TGF-beta and phosphatidylinositol 3-kinase activity

Fibulin-5 (FBLN5), an extracellular matrix glycoprotein required for normal elastogenesis, is coordinately expressed with elastin during lung injury and repair. We found that treatment with transforming growth factor-beta (TGF-beta) induced a rapid but transient increase in FBLN5 heterogeneous nuclear RNA (hnRNA) followed by a sustained increased in the steady-state level of FBLN5 mRNA. The transcription start site of the human FBLN5 gene was localized at 221 nucleotides upstream of the translation start site by using primer extension, Northern blots, and functional analysis of transcriptional activity in reporter plasmids containing 5'-flanking regions. TGF-beta markedly increased FBLN5 promoter activity in transient transfection assays. Two putative Smad-binding sites were identified within the proximal promoter and are required for this TGF-beta induction. Electrophoretic gel mobility shift assay revealed that TGF-beta strongly increased binding of Smad2 and Smad3 nuclear complexes to the proximal FBLN5 promoter and induced a Smad2/3-dependent binding of slow migrating nuclear protein complex. FBLN5 mRNA induction by TGF-beta was blocked by pretreatment with TGF-beta receptor inhibitor SB-431542, the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor LY-294002, and actinomycin D. Basal and TGF-beta-induced FBLN5 hnRNA and mRNA were strongly and proportionally decreased by LY-294002, as was TGF-beta-induced phosphorylation of Akt, but not Smad3, as measured by Western blot analysis. In addition, LY-294002 markedly and proportionally decreased FBLN5 promoter activity in transient transfection analyses with TGF-beta-treated or untreated lung fibroblasts. These studies demonstrate that induction of FBLN5 gene expression in lung fibroblasts is mediated via canonical TGF-beta/Smad signaling and requires the PI3-kinase/Akt pathway.

Interleukin-1beta induces osteopontin expression in pulmonary fibroblasts

Osteopontin is a multifunctional matricellular protein identified as one of the most upregulated genes in pulmonary fibrosis. Experimental animal models have identified early pro-fibrotic cytokines as essential to the pathogenesis of inflammation-induced pulmonary fibrosis. However, the principal sources of osteopontin in the fibroproliferative lung, and the factors responsible for its induction, have not been fully defined. We isolated primary rat lung fibroblasts in culture to examine the expression and regulation of lung fibroblast-derived osteopontin. Our results demonstrate a potent and dramatic increase in osteopontin expression induced by interleukin-1beta (IL-1beta), whereas tumor necrosis factor-alpha, transforming growth factor-beta, and angiotensin II had minimal effect. Stimulation with IL-1beta resulted in the secretion of soluble osteopontin protein. We found that osteopontin expression by IL-1beta was regulated via signaling primarily through the mitogen-activated protein kinase member ERK1/2, partially by p38 MAPK, but not at all by JNK. Finally, the mechanism of IL-1beta increase in osteopontin mRNA requires de novo transcription and translation. In conclusion, we find that osteopontin is expressed by primary lung fibroblasts and is potently upregulated by the early inflammatory and pro-fibrotic cytokine IL-1beta. Activated fibroblasts may be a significant source of osteopontin production during lung fibrogenesis.

Modulation of amino acid uptake by TGF-β in lung myofibroblasts

Hormones such as insulin, growth factors, and cell stress stimulate system A amino acid transporter. Transforming growth factor-beta (TGF-beta) stimulates amino acid uptake thereby inducing cell proliferation, cellular hypertrophy, and matrix synthesis. Insulin appears to activate amino acid in smooth muscle cells via a phosphatidylinositol 3-kinase (PI3-kinase)-dependent pathway. We examine the effect and interaction of TGF-beta, insulin, and PI3-kinase activity on amino acid uptake in human lung myofibroblasts. TGF-beta treatment induced large increases in system A activity and a small delayed increase in the phosphorylation of protein kinase B, also termed phospho-Akt. In contrast, insulin induced small increases in system A activity and large increases in phospho-Akt levels. LY294002, a PI3-kinase inhibitor, blocked the TGF-beta-induced amino acid uptake only partially, but completely blocked TGF-beta-induced Akt phosphorylation. Moreover, the level of phospho-Smad3 was found to be high even when LY294002 blocked TGF-beta-induced phospho-Akt levels. Inhibition of PI3-kinase activity resulted in increase in Km, consistent with a major change in transporter activity without change in transporter number. The PI3-kinase inhibitor also did not change the amino acid transporter 2 (ATA2) mRNA levels. Taken together, these results suggest that TGF-beta induced Smad-3 and amino acid uptake through a PI3-kinase independent pathway.

Hypoxia suppresses elastin repair by rat lung fibroblasts

Macrophage and neutrophil proteinases damage lung elastin, disrupting alveolar epithelium and filling alveoli with inflammatory exudate. Alveolar collapse and regional hypoxia occur. Whether low oxygen tension alters fibroblast-mediated lung repair is unknown. To determine the effect of chronic hypoxia on repair of enzyme-induced elastin disruption, primary rat lung fibroblasts produced elastin matrix for 5 wk before treatment with porcine pancreatic elastase (PPE). After exposure to PPE or saline, cultures recovered for 2 wk in normoxia (21% O2) or hypoxia (3% O2). Hypoxia suppressed regeneration of hot alkali-resistant elastin, achieving only 49% of the repair achieved in normoxic cultures. Vascular smooth muscle cells and lung fibroblasts repair elastin by two pathways: de novo synthesis and salvage repair. Although both pathways were affected, hypoxia predominantly inhibited de novo synthesis, decreasing formation of new elastin matrix by 63% while inhibiting salvage repair by only 36%. Prolonged hypoxia alone downregulated steady-state levels of elastin mRNA by 45%, whereas PPE had no significant effect on elastin gene expression. Electron microscopy documented preservation of intracellular organelles and intact nuclei. Together, these data suggest that regional hypoxia limits lung elastin repair following protease injury at least in part by inhibiting elastin gene expression.

Induction of the myofibroblast phenotype following elastolytic injury to mouse lung

The repair of alveolar structures following endotracheal administration of porcine pancreatic elastase (PPE) to mice involves the coordinated deposition of new matrix elements. We determined the induction of the myofibroblast phenotype following elastolytic injury to mouse lung by examining the expression of alpha-smooth muscle actin (alpha-SMA) by immunohistochemistry. We also examined elastin and alpha1(I) collagen mRNA expression by in situ hybridization. Changes in airspace dimensions were assessed by determining mean linear intercept. In untreated mice, alpha-SMA was localized to vascular structures and large airways, with no detectable expression in alveolar units. PPE induced alpha-SMA expression in damaged areas surrounding large vessels, in septal remnants, and in the opening ring of alveolar ducts. Elastin and alpha1(I) collagen mRNA expression were up-regulated in residual alveolar structures and septal walls. PPE dose-response studies indicated that alpha1(I) collagen and elastin mRNA expression were not induced in areas of normal lung adjacent to damaged lung. The administration of low dose PPE resulted in increased alpha-SMA protein and elastin mRNA expression in the cells comprising the opening ring of alveolar ducts. Our data suggest that repair mechanisms following elastolytic injury are confined to overtly damaged alveolar structures and involve the induction of the myofibroblast phenotype.

Formation of Lung Alveolar-Like Structures in Collagen–Glycosaminoglycan Scaffolds in Vitro

The objective of this study was to investigate the histology of tissue formed when fetal rat lung cells were grown in a collagen-glycosaminoglycan (GAG) tissue-engineering scaffold. The goal was the formation of lung histotypic structures in the tissue-engineering scaffolds in vitro. Achieving this goal would facilitate future investigations of the effects of selected scaffold design parameters on processes that may underlie aspects of lung regeneration in vivo. Lung cells were obtained from Sprague-Dawley rats after 16 and 19 days of gestation. These dissociated cells were seeded into type I collagen-chondroitin 6-sulfate matrices, 8 mm in diameter by 2 mm in thickness, cross-linked and sterilized by dehydrothermal treatment. Approximately 28 million cells were seeded into each spongelike sample. Histological and immunohistochemical studies were performed at termination periods of 2 days and 1, 2, and 3 weeks. The enzymatically dissociated 19-day gestation fetal rat lung cells formed and maintained alveolar-like structures, 50-60 microm in diameter, in the collagen- GAG scaffold. A novel finding was that all of the cell-seeded scaffolds underwent cell-mediated contraction that appeared to be associated with the finding by immunohistochemistry of expression of alpha-smooth muscle actin in some cells. These results demonstrate the capability of dissociated lung cells to form lung histotypic structures in collagen-GAG tissue-engineering scaffolds in vitro. This culture system may be of value in facilitating exploration of strategies for preparing such scaffolds for the regeneration of lung tissue in vivo.

Regulation of elastin gene transcription by proteasome dysfunction

Elastin, a major extracellular matrix protein and the core component of elastic fiber, is essential to maintain lung structural integrity and normal physiological function. We previously found that the downregulation of elastin gene transcription by IL-1β is mediated via activation of NF-κB and CCAAT/enhancer binding protein (C/EBP)β, both targets of the ubiquitin-proteasome pathway. To further investigate the molecular mechanisms that underlie the control of elastin gene expression, we disrupted the ubiquitin-proteasome pathway with specific proteasome inhibitors. We found that specific proteasome inhibitors decreased the steady-state level of elastin mRNA in a dose-responsive manner. Run-on assay and promoter reporter study indicated that the proteasome inhibitor MG-132 repressed the rate of elastin transcription. MG-132 did not affect mRNA levels of NF-κB and C/EBPβ, or the nuclear presence of NF-κB, but markedly increased C/EBPβ isoforms, including liver-enriched transcriptional activating protein and liver-enriched transcriptional inhibitory protein. Addition of cycloheximide blocked these increases and the downregulation of elastin mRNA by MG-132. The MG-132-induced downregulation of elastin transcription was dependent on C/EBPβ expression as assessed with small interfering RNA. These results indicate that the ubiquitin-proteasome pathway plays an essential role in maintaining elastin gene expression in lung fibroblasts. Disruption of this pathway results in the downregulation of tropoelastin transcription via posttranscriptionally induced C/EBPβ isoforms.

Methods for measuring type I collagen synthesis in vitro

The excess accumulation of type I collagen within tissues leads to organ dysfunction and occurs as a result of an imbalance between synthesis and degradation. This chapter outlines several methods to assess the in vitro production of type I collagen that are employed in our laboratory. We describe Western immunoblotting of intact alpha1(I) collagen using antibodies directed to alpha1(I) collagen amino and carboxyl propeptides. The measurement of alpha1(I) collagen mRNA levels using real-time polymerase chain reaction is then outlined. Finally, methods to determine the transcriptional regulation of alpha1(I) collagen using a nuclear run-on assay are described.

Engraftment of neonatal lung fibroblasts into the normal and elastase-injured lung

Interstitial fibroblasts are an integral component of the alveolar wall. These cells produce matrix proteins that maintain the extracellular scaffold of alveolar structures. Emphysema is characterized by airspace enlargement resulting from the loss of alveolar cellularity and matrix. In this study, we explored the endotracheal delivery of fibroblasts to the lung parenchyma as a means of repairing damaged alveolar structures directly or indirectly for the delivery of transgenes. Fibroblasts were isolated from the lungs of neonatal transgenic mice expressing GFP during the period of rapid alveolarization. These GFP+ cells maintained their myofibroblast phenotype in culture and expressed elastin and alpha-smooth muscle actin mRNA. We administered GFP+ fibroblasts to saline- and elastase-treated mice by endotracheal instillation. We detected more GFP+ fibroblasts in the alveolar walls and in the interstitial areas of elastase-injured lungs than in normal lungs as assessed by immunohistochemistry and fluorescent imaging. The presence of GFP+ fibroblasts in the interstitium demonstrated transepithelial migration of these cells. Expression of GFP+ fibroblasts in recipient lungs was maintained for at least 20 d after endotracheal administration. These cells synthesize matrix components including elastin in vitro and could contribute to restoring the structural integrity of the alveolar wall.

Phenylbutyrate decreases type I collagen production in human lung fibroblasts

Fibrotic lung diseases are characterized by excess extracellular matrix production, in particular type I collagen. Phenylbutyrate (PB) is a non-toxic pharmacological compound that functions as a weak histone deacetylase inhibitor. In hepatic stellate cells, the synthesis of type I collagen expression is decreased by inhibiting histone acetylation. Our studies examined the regulation of type I collagen by PB in human lung fibroblasts. We found that PB decreases basal and transforming growth factor-beta-stimulated alpha1(I) collagen mRNA and protein levels. Northern blot analyses demonstrated that PB decreases steady-state alpha1(I) collagen mRNA levels by 78% without significantly changing the stability of the mRNA transcript. PB stimulates cAMP production and increases the acetylation of histone H4, but does not affect the activity of two transforming growth factor-beta (TGF-beta)-responsive luciferase reporter constructs. These data suggest that PB regulates type I collagen expression in human lung fibroblasts by mechanisms that include cAMP production and histone acetylation. PB may have therapeutic use in fibrotic lung diseases.

Elastase Mediates the Release of Growth Factors from LungIn Vivo

Uncontrolled elastase activity is involved in the development of several types of lung disease. Previous reports demonstrated that growth factors are liberated from pulmonary matrix storage sites by elastase; however, release of these entities in vivo is not well defined. In the present study, we investigated the release of fibroblast growth factor-2 (FGF-2) and transforming growth factor-beta (TGF-beta), after intratracheal instillation of porcine pancreatic elastase into mice. We found that elastase promoted a time-dependent release of FGF-2 and TGF-beta1 from the lung into bronchoalveolar lavage (BAL) fluid. A large fraction of the TGF-beta1 in BAL fluid was in the active form (approximately 60%), suggesting that elastase might participate in the activation of TGF-beta1 from its latent form. Analysis of the levels of FGF-2 and TGF-beta1 in mouse blood indicated that the growth factors in BAL fluid were not entirely derived from blood. Moreover, elastase treatment of pulmonary fibroblasts cultures caused the release of TGF-beta1, suggesting that the TGF-beta1 in BAL fluid could have come from lung cells/matrix. Additional in vitro studies also indicated that TGF-beta1 plays a role in upregulating elastin mRNA levels. These data suggest that elastase releases growth factors from lung that participate in elastolytic injury responses.

Regulation of elastin gene transcription by interleukin-1 beta-induced C/EBP beta isoforms

We previously showed that interleukin (IL)-1beta decreases elastin gene transcription through activation of the NF-kappaB subunit p65 in neonatal rat lung fibroblasts. The present study was undertaken to further explore the molecular mechanisms responsible for the inhibitory effect of IL-1beta on elastin gene transcription. We found that cycloheximide blocked IL-1beta-induced downregulation of elastin mRNA but did not inhibit IL-1beta-induced translocation of p65 into the nucleus. IL-1beta treatment increased CCAAT/enhancer-binding protein (C/EBP)beta mRNA and protein levels including liver-enriched activating protein (LAP) and liver-enriched inhibitory protein (LIP), which was cycloheximide sensitive. C/EBPbeta isoforms bound a GCAAT-containing sequence in the proximal elastin promoter as determined by electrophoretic gel shift studies and confirmed by using specific anti-C/EBPbeta antibodies and by competition studies with oligonucleotides. Transient transfection of LIP expression vectors strongly decreased the transcriptional activity of the cotransfected elastin promoter and decreased levels of endogenous elastin mRNA. We demonstrated that IL-1beta-induced downregulation of elastin mRNA is dependent on NF-kappaB activation and C/EBPbeta expression. These results indicate that IL-1beta treatment activates NF-kappaB, which subsequently induces LIP expression and inhibition of elastin gene transcription.

Coordinate expression of fibulin-5/DANCE and elastin during lung injury repair

Fibulin-5, previously known as DANCE and EVEC, is a secreted extracellular matrix protein that functions as a scaffold for elastin fiber assembly and as a ligand for integrins alphavbeta3, alphavbeta5, and alpha9beta1. Fibulin-5 is developmentally regulated in the lung, and lung air space enlargement develops in mice deficient in fibulin-5. Fibulin-5 is also induced in adult lung following lung injury by hyperoxia. To further examine the role of fibulin-5 during repair of lung injury, we assessed fibulin-5 expression during elastase-induced emphysema in C57/b mice. Mice were treated with either saline or elastase via the trachea, and the lung was examined 20 days after treatment. Fibulin-5 mRNA was induced almost fourfold, whereas elastin mRNA was minimally elevated. Immunohistochemistry studies showed that fibulin-5 was induced in cells within the alveolar wall following elastase treatment. Western analysis demonstrates that fibulin-5 was strongly expressed in isolated primary lung interstitial fibroblasts. Fibulin-5 protein was localized to the fibroblast cell layer in culture, and brief elastase treatment degraded the protein. Intact fibulin-5 did not accumulate in the culture media. Treatment of fibroblasts with the proinflammatory cytokine interleukin-1beta abolished fibulin-5 mRNA expression. Our results indicate that fibulin-5 is coordinately expressed and regulated with elastin in lung fibroblasts and may serve a key role during lung injury and repair.

Retinoic acid does not affect alveolar septation in adult FVB mice with elastase-induced emphysema

BACKGROUND

Administration of ALL-TRANS retinoic acid (ATRA) to adult Sprague-Dawley rats with emphysema induced by porcine pancreatic elastase (PPE) reversed the emphysema perhaps by inducing new alveolar formation.

OBJECTIVE

A study was conducted to determine whether ATRA can induce new alveolar septa and reverse the airspace enlargement caused in adult mice by PPE treatment.

METHODS

48 FVB mice were divided into 6 groups. Three groups received 15 microg of PPE in 0.1 ml of 0.9% saline and 3 groups received 0.1 ml of saline, intratracheally. Starting at day 22, the mice received 12 daily intraperitoneal injections of cottonseed oil, with or without ATRA (12.5 microg or 50 microg). The mice were killed for study 1 day after the last injection.

RESULTS

Measurements of plasma and lung tissue ATRA levels showed statistically significant elevated levels after the 50-microg but not after the 12.5-microg doses of ATRA. In situ hybridization studies of elastin and alpha(1)(I) collagen mRNA expression in pulmonary parenchyma as well as in airways and blood vessels showed no effect of ATRA. Airspace size was determined by the mean linear intercept (Lm) method. The Lm of the groups receiving PPE and ATRA (46.2 +/- 4.1 microm, mean +/- SD) was not significantly different from the group receiving PPE and oil (47.8 +/- 6.0 microm). The Lm for groups receiving saline and ATRA (40.6 +/- 2.5 microm) were not significantly different from the group receiving saline and oil (41.0 +/- 2.7 microm). Comparison of the fixed lung volume data and calculated internal surface area also showed no differences between the control and ATRA-treated groups.

CONCLUSION

ATRA treatment does not affect airspace size or expression of elastin or alpha(1)(I) collagen mRNA in adult FVB mice with PPE-induced emphysema.

Interleukin-4 regulates connective tissue growth factor expression in human lung fibroblasts

Transforming growth factor-beta (TGF-beta) and interleukin-4 (IL-4) have fibrogenic properties and induce extracellular matrix production in a variety of lung diseases. Connective tissue growth factor (CTGF) is a matrix signaling molecule stimulated by TGF-beta that in part mediates alpha1(I) collagen mRNA expression. In these studies, the regulation of CTGF expression by IL-4 in human lung fibroblasts was examined. Following 6 h of stimulation with IL-4, basal CTGF mRNA levels were unchanged as assessed by Northern blot analysis. However, IL-4 attenuated the TGF-beta-stimulated induction of CTGF mRNA expression by 50%. This effect was selective because IL-4 did not affect fibronectin or alpha1(I) collagen mRNA expression induced by TGF-beta. Experiments employing the transcriptional inhibitor actinomycin D suggest that IL-4 did not affect the stability of the CTGF mRNA. Transient transfection assays with 3TP-Lux, a luciferase gene controlled by a TGF-beta inducible promoter, and with a CTGF promoter construct indicate that IL-4 interfered with the TGF-beta-induced transcriptional activation of the CTGF gene.

Bleomycin-induced lung fibrosis in IL-4-overexpressing and knockout mice

The role of IL-4 in the development of lung fibrosis is as yet unclear. Bleomycin (Bleo) or saline (Sal) was injected intratracheally into three groups of C57BL/6J mice: transgenic animals that overexpressed IL-4 (IL-4 TG, n = 14), mice with a targeted knockout mutation of the IL-4 gene (IL-4 KO, n = 11), and wild-type (WT, n = 13) mice. At 14 days, lung fibrosis was evaluated by hydroxyproline measurement and by quantitative image analysis of fibrosis fraction and alveolar wall area fraction. Bronchoalveolar lavage cell counts in all Bleo-treated groups demonstrated an increased percentage of lymphocytes with a corresponding decrease in the percentage of macrophages. Comparing Bleo- to Sal-treated controls within each group of mice showed increases in all lung fibrosis parameters in IL-4 KO and WT, but not in any of the parameters in IL-4 TG mice. The severity of Bleo-induced fibrotic response was decreased in overexpressed IL-4 TG compared with IL-4 KO mice. These data negate a critical profibrotic role for IL-4 in Bleo-induced lung fibrosis.

Comparison of contractile function of diaphragm and cardiac muscle in response to paired electrical stimulation

Paired pacing has been shown to potentiate contractile function of cardiac muscle, and it has been suggested that this may enhance contractile function of diaphragmatic muscle. The primary goal of this study was to study the effect of paired pacing on potentiation of contractile function of diaphragmatic muscle compared to atrial and ventricular myocardium. Diaphragmatic muscle was isolated from mouse and rat, and atrial and ventricular myocardium from dogs. Potentiation was induced by isolated extrastimuli (equal in duration and intensity to the pacing stimulus) and by repetitive extrastimuli (i.e. paired pacing) at a paced rate of 12, 30 and 60 beats/min. Baseline studies were performed while preparations were isometrically contracting at L(max) in oxygenated Krebs-Henseleit solution at 28 degrees C. Maximal force generation in response to a premature stimulus was determined at each rate by scanning the coupling interval between paced beats. Under baseline conditions, diaphragmatic muscle contracted faster than atrial and ventricular muscle. In all tissues, maximum potentiation (increase in force above baseline) was approximately 100% of baseline force, and peak potentiation occurred at shorter coupling intervals with increasing rates of stimulation. Single and paired pacing of diaphragm potentiated the contraction during which the extrastimuli were introduced, while in cardiac muscle, extrastimuli potentiated the contraction following the extrastimulus. The maximum potentiated response occurred when the extrastimulus was introduced prior to the development of peak force in diaphragmatic muscle. In contrast, in atrial and ventricular muscle, a single or paired premature stimulus potentiated the subsequent beat when delivered late during relaxation. In cardiac muscle, maximal potentiation gradually occurred following several repetitive stimuli. Following cessation of single and paired pacing, the beat following the potentiated response immediately returned to baseline in diaphragmatic muscle, while a gradual decline was evident over several subsequent beats in cardiac muscle. Increasing the bath temperature from 28 to 37 degrees C resulted in a leftward shift in the peak potentiated force vs. coupling interval curve without a decline in the magnitude of potentiated force in diaphragmatic muscle. In diaphragm muscle, exposure to ryanodine markedly decreased baseline force and maximal potentiation. We conclude that closely timed extrastimuli applied to diaphragmatic muscle can potentiate developed force in a given contraction, while in cardiac tissue a delayed stimulus potentiates the subsequent beat. These differences in contractile responsiveness are not due to differences in loading conditions, but appear to reflect intrinsic differences in calcium handling.

Halofuginone does not reduce fibrosis in bleomycin-induced lung injury

Halofuginone, a coccidiostatic alkaloid, has anti-fibrotic properties, and may be useful as a therapeutic agent in lung fibrosis. To test this hypothesis we investigated the effect of halofuginone on bleomycin-induced lung fibrosis in Sprague-Dawley rats. Treatment groups included: (1) a single intratracheal (IT) instillation of 1.2U bleomycin, and intraperitoneal (IP) injection of halofuginone (0.5 mg/dose), every other day; (2) IT 1.2U bleomycin and IP distilled water (D.W.), every other day; (3) IT 0.8U bleomycin and daily IP halofuginone (0.5 mg/dose); (4) IT 0.8U bleomycin and daily IP D.W.; (5) IT saline and IP halofuginone, every other day; (6) IT saline and daily IP D.W.; (7) IT 0.625U bleomycin and oral halofuginone (10 mg/kg rodent lab chow); (8) IT 0.625U bleomycin and standard lab chow. Animals were studied 14 days after IT instillation. Lung injury was evaluated by total and differential cell count in bronchoalveolar lavage fluid, by a semi-quantitative morphological index of lung injury, and by biochemical analysis of lung hydroxyproline content. Overt signs of lung injury were apparent in bleomycin-treated rats by all measures. These changes were not affected by treatment with halofuginone, irrespective of the treatment regimen used. This study does not support the use of halofuginone to prevent or ameliorate lung fibrosis.

NF-kappaB induced by IL-1beta inhibits elastin transcription and myofibroblast phenotype

Interleukin (IL)-1beta released after lung injury regulates the production of extracellular matrix components. We found that IL-1beta treatment reduced the rate of elastin gene transcription by 74% in neonatal rat lung fibroblasts. Deletion analysis of the rat elastin promoter detected a cis-acting element located at -118 to -102 bp that strongly bound Sp1 and Sp3 but not nuclear factor (NF)-kappaB. This element mediated IL-1beta-induced inhibition of the elastin promoter. IL-1beta treatment did not affect the level of Sp1 but did induce translocation of the p65 subunit of NF-kappaB. Overexpression of p65 decreased elastin promoter activity and markedly reduced elastin mRNA. Immunoprecipitation studies indicated an interaction between the p65 subunit and Sp1 protein. Microarray analysis of mRNA isolated after overexpression of p65 or treatment with IL-1beta revealed downregulation of alpha-smooth muscle actin and calponin mRNAs. Expression of these genes is associated with the myofibroblast phenotype. These results indicate that IL-1beta activates the nuclear localization of NF-kappaB that subsequently interacts with Sp1 to downregulate elastin transcription and expression of the myofibroblast phenotype.

All-trans-retinoic acid (ATRA) is of no benefit in bleomycin-induced lung injury

All-trans-retinoic acid (ATRA) has anti-fibrotic and antiinflammatory properties, and may be useful as a therapeutic agent in lung fibrosis. To test this hypothesis we investigated the effect of ATRA on bleomycin-induced lung fibrosis in Sprague-Dawley rats. Treatment groups included: (1) a single intratracheal (i.t.) instillation of bleomycin and daily intraperitoneal (i.p.) injection of 0.5 mg/kg per day ATRA; (2) i.t. bleomycin and i.p. ATRA, 2 mg/kg per day, (3) i.t. bleomycin and i.p. diluent (cottonseed oil); (4) i.t. saline and i.p. ATRA, 0.5 mg/kg per day, (5) i.t. saline and i.p. ATRA, 2 mg/kg per day; and (6) i.t. saline and i.p. diluent. Animals were studied 14 days after i.t. instillation. Lung injury was evaluated by total and differential cell count in bronchoalveolar lavage fluid, by a semi-quantitative morphological index of lung injury, and by biochemical analysis of lung hydroxyproline content. Overt signs of lung injury were apparent in bleomycin-treated rats by all measures. These changes were not affected by treatment with ATRA at either dose. This study does not support the use of ATRA to prevent or ameliorate lung fibrosis.

Severity of elastase-induced emphysema is decreased in tumor necrosis factor-alpha and interleukin-1beta receptor-deficient mice

A single intratracheal dose of porcine pancreatic elastase, which is cleared from the lung by 24 hours, was administered to wild-type, IL-1beta type 1 receptor-deficient, double TNF-alpha (type 1 and type 2) receptor-deficient, and combined TNF-alpha (type 1 receptor) plus IL-1beta receptor-deficient mice. The mean linear intercept (Lm) of saline-treated mice was 32(3) microm [mean(SE)]. For wild-type elastase-treated mice, Lm was 81(6) microm at 21 days versus 52(5) microm at 5 days after treatment, indicating that alveolar wall remodeling occurs long after the elastase injury. At 21 days, Lm values were 67(10), 62(3), and 39(5) microm in elastase-treated mice deficient in the IL-1beta receptor, double TNF-alpha receptors, and combined receptors, respectively. The level of apoptosis assessed by a terminal deoxynucleotidyl transferase-catalyzed in situ nick end-labeling assay was increased at 5 days after elastase treatment and was markedly and similarly attenuated in the IL-1beta, the double TNF-alpha, and the combined receptor-deficient mice. Our results indicate that inflammatory mediators exacerbate elastase-induced emphysema. We estimate that in the combined TNF-alpha + IL-1beta receptor-deficient mice, inflammation accounts for about 80% of the emphysema that develops after elastase treatment; decreased apoptosis of lung cells likely contributes to decreased severity of emphysema.

Apigenin decreases expression of the myofibroblast phenotype

We investigated the effect of the dietary flavonoid apigenin on myofibroblast function. We report that in myofibroblasts treated with apigenin, proliferation and basal levels of alpha1(I) collagen and alpha-smooth muscle actin mRNAs were markedly reduced. Apigenin also attenuated the transforming growth factor-beta-stimulated increases of alpha1(I) collagen and alpha-smooth muscle actin mRNAs. Characterization of the apigenin effects indicates that apigenin reduces both the stability of the alpha1(I) collagen mRNA and the rate of transcription of the alpha1(I) collagen gene through a cycloheximide-sensitive pathway. Western blot analyses indicate that Akt activity is reduced in apigenin-treated myofibroblasts.

Human recombinant interferon-alpha2a and interferon-alphaA/D have different effects on bleomycin-induced lung injury

BACKGROUND

Bleomycin (Bleo)-induced lung injury in mice serves as an animal model of pulmonary fibrosis. The pathogenesis of pulmonary fibrosis remains unclear, but it comprises both inflammatory and fibrotic components. The cytokine interferon (IFN)-alpha is produced by macrophages and may modulate both fibrogenesis and the determination of T lymphocyte phenotype in pulmonary fibrosis.

OBJECTIVE

To investigate the effect of two preparations of recombinant IFN-alpha (IFN-alphaA/D and IFN-alpha2a) on Bleo-induced lung injury in C57BL/6 mice.

METHODS

Mice were treated by a single intratracheal (IT) instillation of 0.06 mg of Bleo in 0.1 ml of saline or saline alone. One of two different IFN-alpha preparations, IFN-alphaA/D or IFN-alpha2a in saline, or saline alone were administered by daily intraperitoneal injections starting 1 day prior to IT instillation. The treatment groups were as follows: IT Bleo and intraperitoneal saline; IT Bleo and intraperitoneal IFN-alpha2a; IT Bleo and intraperitoneal IFN-alphaA/D; IT saline and intraperitoneal IFN-alphaA/D or IFN-alpha2a; IT saline and intraperitoneal saline. The animals were sacrificed 14 days after IT instillation. Lung injury was evaluated by total and differential cell count in bronchoalveolar lavage (BAL) fluid, by a semiquantitative morphological index of lung injury and a quantitative image analysis of cellularity and fibrosis fraction and by biochemical analysis of lung hydroxyproline content.

RESULTS

In Bleo-treated mice, IFN-alpha2a treatment caused a significant rise in BAL lymphocytes and in cellularity and fibrosis fractions in lung tissue. In contrast, IFN-alphaA/D treatment had no effect on Bleo-induced lung injury.

CONCLUSION

IFN-alpha may enhance Bleo-induced lung injury but this effect varies with different IFN preparations.

Phosphatidylinositol 3-kinase-dependent stabilization of alpha1(I) collagen mRNA in human lung fibroblasts

We investigated the role of phosphatidylinositol 3-kinase (PI3K) in the expression of alpha1(I) collagen mRNA. We report that the basal level of alpha1(I) collagen mRNA was reduced when PI3K activity was inhibited by either LY-294002 or wortmannin. These PI3K inhibitors also blocked increases of alpha1(I) collagen mRNA levels after the addition of transforming growth factor-beta. The effect of PI3K inhibition was abolished by the removal of the inhibitor or by the addition of cycloheximide. Inhibition of PI3K activity decreased the stability of the alpha1(I) collagen mRNA with no change in the rate of transcription of the alpha1(I) collagen gene as assessed by Northern blotting with actinomycin D-treated fibroblasts and nuclear run-on assays. Expression of a truncated alpha1(I) collagen minigene driven by a cytomegalovirus promoter in murine fibroblasts was decreased by LY-294002 treatment. These data indicate that PI3K activation results in increased stabilization of alpha1(I) collagen mRNA. In vivo, the PI3K activity in fibroblasts may regulate basal levels of alpha1(I) collagen mRNA expression.

The effect of suramin on bleomycin-induced lung injury

Since transforming growth factor beta (TGF-beta) is presumed to play a role in lung fibrosis, we evaluated the effect of suramin (Sur), a substance with an anti-TGF-beta effect, in vivo on bleomycin (Bleo)-induced pulmonary injury in mice and in vitro on human lung fibroblasts. Four groups of C57BL/6 mice each received one of four treatments: (1) intratracheal (i.t.) instillation of Bleo and intraperitoneal (i.p.) injections of Sur, every other day, starting one day before i.t. instillation of Bleo (Bleo-Sur); (2) i.t. Bleo and i.p. injections of saline (Bleo-Sal); (3) i.t. saline and i.p. Sur (Sal-Sur); and (4) i.t. and i.p. saline (Sal-Sal). Animals were sacrificed 14 days after i.t. treatment. Lung injury was evaluated by analysis of bronchoalveolar lavage (BAL) fluid, histologically by the semiquantitative morphological index, and biochemically by analysis of lung hydroxyproline content. In vitro, Sur did not affect TGF-beta induced increase of alpha1 (I) collagen mRNA in human lung fibroblasts. In vivo treatment of mice with Sur did not affect Bleo-induced lung injury. These results indicate that despite its potential anti TGF-beta and lymphocytotoxic effects, Sur is not a therapeutic candidate drug for rescue of lung fibrosis.

Hypoxia inhibits amino acid uptake in human lung fibroblasts

Hypoxia and amino acid deprivation downregulate expression of extracellular matrix genes in lung fibroblasts. We examined the effect of hypoxia on amino acid uptake and protein formation in human lung fibroblasts. Low O(2) tension (0% O(2)) suppressed incorporation of [(3)H]proline into type I collagen without affecting [(35)S]methionine labeling of other proteins. Initial decreases in intracellular [(3)H]proline incorporation occurred after 2 h of exposure to 0% O(2), with maximal suppression of intracellular [(3)H]proline levels at 6 h of treatment. Hypoxia significantly inhibited the uptake of radiolabeled proline, 2-aminoisobutyric acid (AIB), and 2-(methylamino)isobutyric acid (methyl-AIB) while inducing minor decreases in leucine transport. Neither cycloheximide nor indomethacin abrogated hypoxia-related suppression of methyl-AIB uptake. Efflux studies demonstrated that hypoxia inhibited methyl-AIB transport in a bidirectional fashion. The downregulation of amino acid transport was not due to a toxic effect; function recovered on return to standard O(2) conditions. Kinetic analysis of AIB transport revealed a 10-fold increase in K(m) accompanied by a small increase in maximal transport velocity among cells exposed to 0% O(2). These data indicate that low O(2) tension regulates the system A transporter by decreasing transporter substrate affinity.

Activation of Na + /Ca 2+ Exchanger in Kinin B 1 Receptor-Stimulated Human Fibroblast Is Associated with Collagen Production

P148

The arterial wall in hypertension is characterized by thickening of the media, in part due to increased deposition of connective tissue. Autocrine and paracrine factors may participate in this process; including products of the kallikrein-kinin system. We evaluated early signal transduction events and effects on collagen formation in B 1 -stimulated human myofibroblast cells (IMR-90). We measured cytosolic calcium (Ca cyt ) levels in cells loaded with FURA-2AM. Gene expression of connective tissue growth factor (CTGF) and α1(I) collagen was determined by estimating mRNA levels using Northern analysis of B 1 stimulated cells. Activation of the B 1 receptor with des-arg 10 -kallidin stimulated a three-fold increase in CTGF mRNA by increasing its stability. Furthermore, B 1 receptor activation caused an increase in α1(I) collagen mRNA and a four-fold increase in type I collagen synthesis in these cells; events not observed in B 2 receptor-stimulated cells. Activation of the B 1 receptor stimulated a dose dependent rise in Ca cyt (EC 50 =1.9nM) which was completely inhibited by des-arg 10 -[leu 9 ]-kallidin (100nM), a B 1 receptor antagonist. Isosmotic replacement of extracellular Na + with N -methyl,D-glucamine blocked > 90% of the B 1 stimulated rise in Ca cyt . A similar effect was observed when Ca 2+ was removed from the extracellular media, suggesting a role for the plasma membrane Na + /Ca 2+ exchanger (NCX). To further define a role for the NCX on CTGF formation we used dichlorobenzamil (DCB) and KB-R7943, two specific NCX inhibitors. DCB completely blocked the activation of B 1 receptor induced increase in CTGF mRNA stability while not affecting basal CTGF mRNA levels. In contrast, preincubation with EIPA, an amiloride analog, did not affect basal or stimulated CTGF mRNA levels. Furthermore, 60μM KB-R7943 blocked the B 1 stimulated rise in Ca cyt . NCX isoform 1 was identified in these cells using RT-PCR and immuno-detection. Thus, B 1 receptor stimulation increases fibrogenesis through a mechanism that involves modulation of cation metabolism via reverse-mode activation of NCX.

Des-Arg(10)-kallidin engagement of the B1 receptor stimulates type I collagen synthesis via stabilization of connective tissue growth factor mRNA

Expression of the kinin B1 receptor is up-regulated in chronic inflammatory and fibrotic disorders; however, little is known about its role in fibrogenesis. We examined human embryonic lung fibroblasts that constitutively express the B1 receptor and report that engagement of the B1 receptor by des-Arg(10)-kallidin stabilized connective tissue growth factor (CTGF) mRNA, stimulated an increase in alpha1(I) collagen mRNA, and stimulated type I collagen production. These events were not observed in B2 receptor-activated fibroblasts. In addition, B1 receptor activation by des-Arg(10)-kallidin induced a rise in cytosolic Ca(2+) that is consistent with B1 receptor pharmacology. Our results show that the des-Arg(10)-kallidin-stimulated increase in alpha1(I) collagen mRNA was time- and dose-dependent, with a peak response observed at 20 h with 100 nM des-Arg(10)-kallidin. The increase in CTGF mRNA was also time- and dose-dependent, with a peak response observed at 4 h with 100 nM des-Arg(10)-kallidin. The increase in CTGF mRNA was blocked by the B1 receptor antagonist des-Arg(10),Leu(9)-kallidin. Inhibition of protein synthesis by cycloheximide did not block the des-Arg(10)-kallidin-induced increase in CTGF mRNA. These results suggest that engagement of the kinin B1 receptor contributes to fibrogenesis through increased expression of CTGF.

Regulation of connective tissue growth factor expression by prostaglandin E(2)

Transforming growth factor-beta (TGF-beta) stimulates alpha(1)(I) collagen mRNA synthesis in human lung fibroblasts through a mechanism that is partially sensitive to cycloheximide and that may involve synthesis of connective tissue growth factor (CTGF). Northern blot analyses indicate that TGF-beta stimulates time- and dose-dependent increases in CTGF mRNA. In TGF-beta-stimulated fibroblasts, maximal levels of CTGF mRNA (3.7-fold above baseline) occur at 6 h. The TGF-beta-stimulated increase in CTGF mRNA was not blocked by cycloheximide. Nuclear run-on analysis indicates that TGF-beta increases the CTGF transcription rate. The TGF-beta-stimulated increases in CTGF transcription and steady-state levels of CTGF mRNA are attenuated in prostaglandin E(2) (PGE(2))-treated fibroblasts. PGE(2) fails to attenuate luciferase activity induced by TGF-beta in fibroblasts transfected with the TGF-beta-responsive luciferase reporter construct p3TP-LUX. In amino acid-deprived fibroblasts, PGE(2) and insulin regulate alpha(1)(I) collagen mRNA levels without affecting CTGF mRNA levels. The data suggest that the regulation of alpha(1)(I) collagen mRNA levels by TGF-beta and PGE(2) may function through both CTGF-dependent and CTGF-independent mechanisms.

Effect of immunomodulators on bleomycin-induced lung injury

BACKGROUND

The role of lymphocytes and their subpopulations in lung fibrosis is as yet unclear.

OBJECTIVE

To define the role of immunomodulation in bleomycin-induced inflammatory fibrotic lung injury, by testing the effect of two known Th1 inhibitors: linomide and pentoxifylline.

METHODS

C57BL/6 mice were treated by a single intratracheal instillation of 0.06 mg bleomycin in 0.01 ml saline or saline alone. Treatment groups included: (1) intratracheal bleomycin and daily treatment with linomide or pentoxifylline; (2) intratracheal bleomycin and daily water; (3) intratracheal saline and daily linomide or pentoxifylline; (4) intratracheal saline and daily water. Linomide and pentoxifylline were available per os in the drinking water from 1 day prior to intratracheal instillation. Animals were studied 14 days after intratracheal instillation. Lung injury was evaluated by total and differential cell count in bronchoalveolar lavage fluid, by a semiquantitative morphological index of lung injury and a quantitative image analysis of cellularity, fibrosis fraction and alveolar wall area fraction, and by biochemical analysis of lung hydroxyproline content.

RESULTS

Linomide or pentoxifylline did not cause any lung injury in saline-treated control mice. Overt signs of lung injury were apparent in bleomycin-treated mice. These changes were not affected by daily treatment with linomide or pentoxifylline, which were given in the highest tolerable dose.

CONCLUSION

This study does not support the use of linomide or pentoxifylline to prevent or ameliorate lung fibrosis and may suggest that drug-induced differentiation of T lymphocytes into Th1/th2 subpopulations does not affect the evolution of bleomycin-induced lung injury.

Amino acid availability regulates type I procollagen accumulation in human lung fibroblasts

Fibrotic lung diseases are characterized by excessive deposition of type I collagen. Amino acid availability regulates type I collagen mRNA levels in quiescent human lung fibroblasts. In these studies, the effect of amino acid availability on type I collagen protein accumulation in quiescent human lung fibroblasts was examined. Following amino acid deprivation, alpha1(I) procollagen protein levels were not detected by Western blot analysis in either the intracellular or the extracellular compartments. Fibronectin levels and total protein levels were not affected. Amino acid deprivation resulted in a more pronounced decrease in alpha1(I) procollagen protein levels than in alpha1(I) procollagen mRNA levels, suggesting that post-transcriptional events were responsible for the further decrease inalpha1(I) procollagen protein levels. The addition of transforming growth factor-beta to amino acid deprived fibroblasts increased alpha1(I) procollagen mRNA levels without affecting alpha1(I) procollagen protein levels, confirming a post-transcriptional site for regulatory control by amino acid deprivation. In the absence of ascorbic acid, alpha1(I) procollagen protein levels increased in amino acid deprived fibroblasts, but alpha1(I) procollagen mRNA levels were not affected. The absence of ascorbic acid likely resulted in the accumulation of nonhelical procollagen in the endoplasmic reticulum, indicating that translational mechanisms for alpha1(I) procollagen were intact. The addition of chloroquine, an inhibitor of lysosomal degradation of proteins, increased alpha1(I) procollagen protein levels in amino acid deprived fibroblasts. These data suggest that following amino acid deprivation of quiescent fibroblasts, newly synthesized type I collagen was degraded intracellularly, primarily by a process that involved lysosomal proteinases.

The effect of enoxaparin on bleomycin-induced lung injury in mice

We have evaluated the effect of enoxaparin, a potent antithrombotic drug, on bleomycin (Bleo)-induced pulmonary inflammation in mice. Pulmonary injury was induced by a single intratracheal (i.t.) instillation of Bleo. Four groups of female C57BL/6 mice, each received one of four treatments: (1) i.t. Bleo and daily intraperitoneal (i.p.) injections of enoxaparin (EN) starting one day before i.t. instillation of Bleo (Bleo-EN); (2) i.t. Bleo and i.p. injections of saline (Bleo-Sal); (3) i.t. saline and i.p. enoxaparin (Sal-EN); (4) i.t. saline and i.p. saline (Sal-Sal). Animals were sacrificed 14 days after i.t. treatment. Lung injury was evaluated by analysis of bronchoalveolar lavage fluid and histologically by an overall semiquantitative index of lung injury and a quantitative image analysis assessing alveolar wall area fraction and fibrosis fraction. Treatment of mice with enoxaparin did not ameliorate Bleo-induced lung injury. Our study does not establish a critical role of procoagulant activity in the evolution of Bleo-induced lung injury and does not support the use of antithrombotic therapy for the prevention of pulmonary fibrosis.

Hypoxia downregulates tropoelastin gene expression in rat lung fibroblasts by pretranslational mechanisms

Elastolytic lung injury disrupts cell barriers, flooding alveoli and producing regional hypoxia. Abnormal O2 tensions may alter repair of damaged elastin fibers. To determine the effect of hypoxia on extravascular elastin formation, we isolated rat lung fibroblasts and cultured them under a variety of O2 conditions. Hypoxia downregulated tropoelastin mRNA in a dose- and time-related fashion while upregulating glyceraldehyde-3-phosphate dehydrogenase mRNA levels. The changes in tropoelastin gene expression were not due to cell toxicity as measured by chromium release and cell proliferation studies. Neither cycloheximide nor actinomycin D abrogated this effect. Hypoxia induced early decreases in tropoelastin mRNA stability; minor suppression of gene transcription occurred later. When returned to 21% O2, tropoelastin mRNA recovered to control levels in part by upregulating tropoelastin gene transcription. Taken together, these data indicate that hypoxia regulates tropoelastin gene expression and may alter repair of acutely injured lung.

The effect of prostaglandin E2 on cystine uptake and glutathione synthesis by human lung fibroblasts

Prostaglandin E2 (PGE2) is an inflammatory mediator capable of regulating fibroblast cell proliferation, matrix protein production, and system A amino acid transport. System x-c amino acid transport is regulated by electrophilic agents and oxygen. The effect of PGE2 on the x-c system transport of cystine and the synthesis of glutathione by human lung fibroblasts was examined. Preincubation of fibroblast cultures with PGE2 decreased cystine uptake by 42%. Kinetic studies revealed a 42% decrease in the Vmax of the x-c system transporter in PGE2-treated fibroblasts; however, the apparent Km was not affected. The glutathione content of PGE2-treated fibroblasts was decreased by up to 25% of control. These results demonstrate that system x-c transport of cystine is regulated by PGE2 and suggest that the limited availability of intracellular cysteine inhibited glutathione synthesis.

Remodeling of alveolar walls after elastase treatment of hamsters. Results of elastin and collagen mRNA in situ hybridization

Treatment of hamster lungs with porcine pancreatic elastase (PPE) causes emphysema and a decrease in lung elastin content, which returns to control level by Day 30. To explore the mechanism of alveolar wall remodeling after elastolytic injury, we examined the expression of elastin and alpha1(I) collagen mRNAs by in situ hybridization at 1, 2, 3, 5, 7, and 30 d after intratracheal PPE. The lungs of control animals displayed weak signals for elastin and alpha1(I) collagen mRNA in pleura, large arteries, veins, and airways. There was little or no signal in respiratory air space walls. Increased expression of elastin and alpha1(I) collagen mRNA began by Day 1 after PPE and reached an asymptote by Day 3 that was maintained by elastin until Day 7; expression of alpha1(I) collagen mRNA waned earlier. Elastin and, to a lesser extent, alpha1(I) collagen mRNA were heavily expressed in pleura, blood vessels, and airways. Analysis of serial sections showed elastin message was minimal in the walls of respiratory air spaces and when present, at 3, 5, and 7 d, was primarily found at the free margins of alveolar septa. Collagen message was very sparse in respiratory air space walls. By 30 d, elastin mRNA expression was reduced but still above control levels and emphysema was widespread and severe. Rank score of elastin mRNA expression in individual subpleural air spaces showed a positive correlation with air space size. In conclusion, most expression of elastin and alpha1(I) collagen mRNA occurs in the pleura, airway, and vascular walls. In respiratory air space walls, expression of elastin mRNAs occurs in damaged tissue at free septal margins.

Regulation of type I collagen mRNA in lung fibroblasts by cystine availability

The steady-state level of alpha1(I) collagen mRNA is regulated by amino acid availability in human lung fibroblasts. Depletion of amino acids decreases alpha1(I) collagen mRNA levels and repletion of amino acids induces rapid re-expression of alpha1(I) mRNA. In these studies, we examined the requirements for individual amino acids on the regulation of alpha1(I) collagen mRNA. We found that re-expression of alpha1(I) collagen mRNA was critically dependent on cystine but not on other amino acids. However, the addition of cystine alone did not result in re-expression of alpha1(I) collagen mRNA. Following amino acid depletion, the addition of cystine with selective amino acids increased alpha1(I) collagen mRNA levels. The combination of glutamine and cystine increased alpha1(I) collagen mRNA levels 6.3-fold. Methionine or a branch-chain amino acid (leucine, isoleucine or valine) also acted in combination with cystine to increase alpha1(I) collagen mRNA expression, whereas other amino acids were not effective. The prolonged absence of cystine lowered steady-state levels of alpha1(I) collagen mRNA through a mechanism involving decreases in both the rate of gene transcription as assessed by nuclear run-on experiments and mRNA stability as assessed by half-life determination in the presence of actinomycin D. The effect of cystine was not mediated via alterations in the level of glutathione, the major redox buffer in cells, as determined by the addition of buthionine sulphoximine, an inhibitor of gamma-glutamylcysteine synthetase. These data suggest that cystine directly affects the regulation of alpha1(I) collagen mRNA.

Colchicine does not ameliorate bleomycin-induced pulmonary injury in hamsters

We have evaluated the effect of colchicine, a potential antifibrotic drug, on bleomycin-induced pulmonary inflammation in hamsters. Pulmonary injury was induced by a single intratracheal (IT) instillation of bleomycin (bleo). Four groups of male Syrian hamsters each received one of four treatments: (1) IT bleo and twice daily intraperitoneal (IP) injections of colchicine (col) starting one day before IT instillation of bleo (bleo-col); (2) IT bleo and IP injections of saline (bleo-sal); (3) IT saline and IP colchicine (sal-col); and (4) IT saline and IP saline (sal-sal). Animals were sacrificed 28 days after IT treatment. Lung injury was evaluated histologically, biochemically and by analysis of bronchoalveolar lavage (BAL) fluid. Treatment of hamsters with colchicine did not ameliorate the bleo-induced lung injury, as determined by a semiquantitative morphological index that assesses the severity and extent of the lung injury on a scale of 0-3. Lung hydroxyproline measurements and BAL fluid cell count were also similar in bleo-col compared to bleo-sal hamsters. Colchicine did not prevent the bleo-induced restriction expressed by volume displacement. These results indicate that colchicine does not ameliorate the bleo-induced lung inflammation and fibrosis and call for further controlled investigations to justify the use of this drug in pulmonary disorders.