Abnormal circulating steroids refine risk of progression to heart failure in ischemic heart disease.

BACKGROUND: Patients with ischemic heart disease (IHD) experience a high incidence of progression to heart failure (HF) despite current therapies. We speculated that steroid hormone metabolic disorders distinct adverse phenotypes and contribute to HF. METHODS: We measured 18 steroids using liquid chromatography with tandem mass spectrometry in 2023 patients from the Registry Study of Biomarkers in Ischemic Heart Disease (BIOMS-IHD), including 1091 patients with IHD in a retrospective discovery set and 932 patients with IHD in a multicentre validation set. Our outcomes included incident HF after a median follow-up of 4 years. RESULTS: We demonstrated steroid-based signatures of inflammation, coronary microvascular dysfunction and left ventricular hypertrophy that were associated with subsequent HF events in patients with IHD. In both cohorts, patients with a high steroid-heart failure score (SHFS) (>1) exhibited a greater risk of incident HF than patients with a low SHFS (≤1). The SHFS further improved the prognostic accuracy beyond clinical variables (net reclassification improvement of 0.628 in the discovery set and 0.299 in the validation set) and demonstrated the maximal effect of steroid signatures in patients with IHD who had lower B-type natriuretic peptide levels (pinteraction = 0.038). CONCLUSIONS: A steroid-based strategy can simply and effectively identify individuals at higher HF risk who may derive benefit from more intensive follow-ups.

α1 Adrenoreceptor antagonism mitigates extracellular mitochondrial DNA accumulation in lung fibrosis models and in patients with idiopathic pulmonary fibrosis.

Idiopathic pulmonary fibrosis is increasingly associated with nerve-driven processes and endogenous innate immune ligands such as mitochondrial DNA (mtDNA). Interestingly, a connection between these entities has not been explored. Here, we report that noradrenaline (NA) derived from the lung's adrenergic nerve supply drives α-smooth muscle actin (αSMA)-expressing fibroblast accumulation via mechanisms involving α1 adrenoreceptors and mtDNA. Using the bleomycin model, we compared ablation of the lung's adrenergic nerve supply with surgical adrenal resection and found that NA derived from local but not adrenal sources contributes to experimentally induced lung fibrosis and the emergence of an αSMA+ve fibroblast population expressing adrenoreceptor α-1D (ADRA1D). Therapeutic delivery of the α1 adrenoreceptor antagonist terazosin reversed these changes and suppressed extracellular mtDNA accumulation. Cultured normal human lung fibroblasts displayed α1 adrenoreceptors and in response to costimulation with TGFß1 and NA adopted ACTA2 expression and extracellular mtDNA release. These findings were opposed by terazosin. Evaluation of a previously studied IPF cohort revealed that patients prescribed α1 adrenoreceptor antagonists for nonpulmonary indications demonstrated improved survival and reduced concentrations of plasma mtDNA. Our observations link nerve-derived NA, α1 adrenoreceptors, extracellular mtDNA, and lung fibrogenesis in mouse models, cultured cells, and humans with IPF. Further study of this neuroinnate connection may yield new avenues for investigation in the clinical and basic science realms.

Diversity of bacterial communities in the plasmodia of myxomycetes.

BACKGROUND: Myxomycetes are a group of eukaryotes belonging to Amoebozoa, which are characterized by a distinctive life cycle, including the plasmodium stage and fruit body stage. Plasmodia are all found to be associated with bacteria. However, the information about bacteria diversity and composition in different plasmodia was limited. Therefore, this study aimed to investigate the bacterial diversity of plasmodia from different myxomycetes species and reveal the potential function of plasmodia-associated bacterial communities. RESULTS: The bacterial communities associated with the plasmodia of six myxomycetes (Didymium iridis, Didymium squamulosum, Diderma hemisphaericum, Lepidoderma tigrinum, Fuligo leviderma, and Physarum melleum) were identified by 16S rRNA amplicon sequencing. The six plasmodia harbored 38 to 52 bacterial operational taxonomic units (OTUs) that belonged to 7 phyla, 16 classes, 23 orders, 40 families, and 53 genera. The dominant phyla were Bacteroidetes, Firmicutes, and Proteobacteria. Most OTUs were shared among the six myxomycetes, while unique bacteria in each species only accounted for a tiny proportion of the total OTUs. CONCLUSIONS: Although each of the six myxomycetes plasmodia had different bacterial community compositions, a high similarity was observed in the plasmodia-associated bacterial communities' functional composition. The high enrichment for gram-negative (> 90%) and aerobic (> 99%) bacteria in plasmodia suggest that myxomycetes may positively recruit certain kinds of bacteria from the surrounding environment.

Plexin C1 deficiency permits synaptotagmin 7-mediated macrophage migration and enhances mammalian lung fibrosis.

Pulmonary fibrosis is a progressive and often fatal condition that is believed to be partially orchestrated by macrophages. Mechanisms that control migration of these cells into and within the lung remain undefined. We evaluated the contributions of the semaphorin receptor, plexin C1 (PLXNC1), and the exocytic calcium sensor, synaptotagmin 7 (Syt7), in these processes. We evaluated the role of PLXNC1 in macrophage migration by using Boyden chambers and scratch tests, characterized its contribution to experimentally induced lung fibrosis in mice, and defined the mechanism for our observations. Our findings reveal that relative to control participants, patients with idiopathic pulmonary fibrosis demonstrate excessive monocyte migration and underexpression of PLXNC1 in the lungs and circulation, a finding that is recapitulated in the setting of scleroderma-related interstitial lung disease. Relative to wild type, PLXNC1-/- mouse macrophages are excessively migratory, and PLXNC1-/- mice show exacerbated collagen accumulation in response to either inhaled bleomycin or inducible lung targeted TGF-ß1 overexpression. These findings are ameliorated by replacement of PLXNC1 on bone marrow-derived cells or by genetic deletion of Syt7. These data demonstrate the previously unrecognized observation that PLXNC1 deficiency permits Syt7-mediated macrophage migration and enhances mammalian lung fibrosis.-Peng, X., Moore, M., Mathur, A., Zhou, Y., Sun, H., Gan, Y., Herazo-Maya, J. D., Kaminski, N., Hu, X., Pan, H., Ryu, C., Osafo-Addo, A., Homer, R. J., Feghali-Bostwick, C., Fares, W. H., Gulati, M., Hu, B., Lee, C.-G., Elias, J. A., Herzog, E. L. Plexin C1 deficiency permits synaptotagmin 7-mediated macrophage migration and enhances mammalian lung fibrosis.

Fibroblast engraftment in the decellularized mouse lung occurs via a ß1-integrin-dependent, FAK-dependent pathway that is mediated by ERK and opposed by AKT.

Creation of bioartificial organs has been enhanced by the development of strategies involving decellularized mammalian lung. Because fibroblasts critically support lung function through a number of mechanisms, study of these cells in the context of the decellularized lung has the potential to improve the structure and function of tissue-engineered lungs. We characterized the engraftment and survival of a mouse fibroblast cell line in decellularized rat lung slices and found a time-dependent increase in cell numbers assessed by hematoxylin and eosin staining, cell proliferation assessed by Ki67 staining, and minimal cell death assessed by TUNEL staining. We developed a repopulation index to allow quantification of cell survival that accounts for variation in cell density throughout the seeded scaffold. We then applied this method to the study of mouse lung scaffolds and found that decellularization of presliced mouse lungs produced matrices with preserved alveolar architecture and proteinaceous components including fibronectin, collagens I and IV, laminin, and elastin. Treatment with a ß1-integrin-neutralizing antibody significantly reduced the repopulation index after 24 h of culture. Treatment with focal adhesion kinase (FAK) inhibitor and extracellular signal-regulated kinase (ERK) inhibitor further reduced initial repopulation scores while treatment with AKT inhibitor increased initial scores. Rho-associated kinase inhibitor had no discernible effect. These data indicate that initial adhesion and survival of mouse fibroblasts in the decellularized mouse lung occur in a ß1-integrin-dependent, FAK/ERK-dependent manner that is opposed by AKT.

Chitinase 1 is a biomarker for and therapeutic target in scleroderma-associated interstitial lung disease that augments TGF-ß1 signaling.

Interstitial lung disease (ILD) with pulmonary fibrosis is an important manifestation in systemic sclerosis (SSc, scleroderma) where it portends a poor prognosis. However, biomarkers that predict the development and or severity of SSc-ILD have not been validated, and the pathogenetic mechanisms that engender this pulmonary response are poorly understood. In this study, we demonstrate in two different patient cohorts that the levels of chitotriosidase (Chit1) bioactivity and protein are significantly increased in the circulation and lungs of SSc patients compared with demographically matched controls. We also demonstrate that, compared with patients without lung involvement, patients with ILD show high levels of circulating Chit1 activity that correlate with disease severity. Murine modeling shows that in comparison with wild-type mice, bleomycin-induced pulmonary fibrosis was significantly reduced in Chit1⁻/⁻ mice and significantly enhanced in lungs from Chit1 overexpressing transgenic animals. In vitro studies also demonstrated that Chit1 interacts with TGF-ß1 to augment fibroblast TGF-ß receptors 1 and 2 expression and TGF-ß-induced Smad and MAPK/ERK activation. These studies indicate that Chit1 is potential biomarker for ILD in SSc and a therapeutic target in SSc-associated lung fibrosis and demonstrate that Chit1 augments TGF-ß1 effects by increasing receptor expression and canonical and noncanonical TGF-ß1 signaling.

Semaphorin 7a+ regulatory T cells are associated with progressive idiopathic pulmonary fibrosis and are implicated in transforming growth factor-ß1-induced pulmonary fibrosis.

RATIONALE: Lymphocytes are increasingly associated with idiopathic pulmonary fibrosis (IPF). Semaphorin 7a (Sema 7a) participates in lymphocyte activation. OBJECTIVES: To define the relationship between Sema 7a and lymphocytes in IPF. METHODS: We characterized the significance of Sema 7a+ lymphocytes in humans with IPF and in a mouse model of lung fibrosis caused by lung-targeted, transgenic overexpression of TGF-ß1. We determined the site of Sema 7a expression in human and murine lungs and circulation and used adoptive transfer approaches to define the relevance of lymphocytes coexpressing Sema7a and the markers CD19, CD4, or CD4+CD25+FoxP3+ in TGF-ß1-induced murine lung fibrosis. MEASUREMENTS AND MAIN RESULTS: Subjects with IPF show expression of Sema 7a on lung CD4+ cells and circulating CD4+ or CD19+ cells. Sema 7a expression is increased on CD4+ cells and CD4+CD25+FoxP3+ regulatory T cells, but not CD19+ cells, in subjects with progressive IPF. Sema 7a is expressed on lymphocytes expressing CD4 but not CD19 in the lungs and spleen of TGF-ß1-transgenic mice. Sema 7a expressing bone marrow-derived cells induce lung fibrosis and alter the production of T-cell mediators, including IFN-γ, IL-4, IL-17A, and IL-10. These effects require CD4 but not CD19. In comparison to Sema 7a-CD4+CD25+FoxP3+ cells, Sema7a+CD4+CD25+FoxP3+ cells exhibit reduced expression of regulatory genes such as IL-10, and adoptive transfer of these cells induces fibrosis and remodeling in the TGF-ß1-exposed murine lung. CONCLUSIONS: Sema 7a+CD4+CD25+FoxP3+ regulatory T cells are associated with disease progression in subjects with IPF and induce fibrosis in the TGF-ß1-exposed murine lung.

Metabolic signatures in post-myocardial infarction heart failure, including insights into prediction, intervention, and prognosis.

Heart failure (HF) is a prevalent long-term complication of myocardial infarction (MI). The incidence of post-MI HF is high, and patients with the condition have a poor prognosis. Accurate identification of individuals at high risk for post-MI HF is crucial for implementation of a protective and ideally personalized strategy to prevent fatal events. Post-MI HF is characterized by adverse cardiac remodeling, which results from metabolic changes in response to long-term ischemia. Moreover, various risk factors, including genetics, diet, and obesity, can influence metabolic pathways in patients. This review focuses on the metabolic signatures of post-MI HF that could serve as non-invasive biomarkers for early identification in high-risk populations. We also explore how metabolism participates in the pathophysiology of post-MI HF. Furthermore, we discuss the potential of metabolites as novel targets for treatment of post-MI HF and as biomarkers for prognostic evaluation. It is expected to provide valuable suggestions for the clinical prevention and treatment of post-MI HF from a metabolic perspective.

In situ grown Bi2WO6@CoMoO4 layered cladding structure on carbon nanofibers by a two-step solvothermal method and Ti mesh substrate as advanced counter electrodes for dye-sensitized solar cells.

Based on carbon nanofibers (CNFs) with excellent electrical conductivity, a three-layer cladding structure CNFs@Bi2WO6@CoMoO4 material was prepared by a two-step solvothermal method, which effectively combines the great catalytic ability of transition metal oxides with the good conductivity of CNFs. Titanium (Ti) mesh was used as the conductive substrate and CNFs@Bi2WO6@CoMoO4 was scraped on it to prepare paired counter electrodes (CEs), and then dye-sensitized solar cells (DSSCs) were assembled by unifying with photoanode and iodine electrolyte. The photoelectric conversion efficiency (PCE) of 9.41% (with Voc of 0.784 V, Jsc of 17.90 mA cm-2 and FF of 0.72) was obtained under standard light conditions (AM 1.5 G). In brief, this study found a cheaper and better alternative material for Pt and also provides more possibilities for the selection of conductive substrate for CEs.

A Nerve-Fibroblast Axis in Mammalian Lung Fibrosis.

Tissue fibrosis contributes to pathology in vital organs including the lung. Curative therapies are scant. Myofibroblasts, pivotal effector cells in tissue fibrosis, accumulate via incompletely understood interactions with their microenvironment. In an investigative platform grounded in experimental lung biology, we find that sympathetic innervation stimulates fibrotic remodeling via noradrenergic α1-adrenergic receptor engagement in myofibroblasts. We demonstrate the anti-fibrotic potential of targeted sympathetic denervation and pharmacological disruption of noradrenergic neurotransmitter functions mediated by α1-adrenoreceptors (α1-ARs). Using the α1-adrenoreceptor subtype D as a representative α1-AR, we discover direct noradrenergic input from sympathetic nerves to lung myofibroblasts utilizing established mouse models, genetic denervation, pharmacologic interventions, a newly invented transgenic mouse line, advanced tissue mimetics, and samples from patients with diverse forms of pulmonary fibrosis. The discovery of this previously unappreciated nerve-fibroblast axis in the lung demonstrates the crucial contribution of nerves to tissue repair and heralds a novel paradigm in fibrosis research.

Genome size and GC content of myxomycetes.

More than 1272 myxomycetes species have been described, accounting for more than half of all Amoebozoa species. However, the genome size of only three myxomycetes species has been reported. Therefore, we used flow cytometry to present an extensive survey and a phylogeny-based analysis of genome size and GC content evolution in 144 myxomycetes species. The genome size of myxomycetes ranged from 18.7 Mb to 470.3 Mb, and the GC content ranged from 38.7% to 70.1%. Bright-spored clade showed larger genome sizes and more intra-order genome size variations than the dark-spored clade. GC content and genome size were positively correlated in both bright-spored and dark-spored clades, and spore size was positively correlated with genome size and GC content in the bright-spored clade. We provided the first genome size data set in Myxomycetes, and our results will provide helpful information for future Myxomycetes studies, such as genome sequencing.

Role of semaphorin 7a signaling in transforming growth factor ß1-induced lung fibrosis and scleroderma-related interstitial lung disease.

OBJECTIVE: Semaphorin 7a regulates transforming growth factor ß1 (TGFß1)-induced fibrosis. This study was undertaken to test the hypothesis that semaphorin 7a exerts its profibrotic effects in part by promoting the tissue accumulation of CD45+ fibrocytes. METHODS: A murine model of pulmonary fibrosis in which an inducible, bioactive form of the human TGFß1 gene is overexpressed in the lung was used. Fibrosis and fibrocytes were evaluated in TGFß1-transgenic mice in which the semaphorin 7a locus had been disrupted. The effect of replacement or deletion of semaphorin 7a on bone marrow-derived cells was ascertained using bone marrow transplantation. The role of the semaphorin 7a receptor ß1 integrin was assessed using neutralizing antibodies. The applicability of these findings to TGFß1-driven fibrosis in humans was examined in patients with scleroderma-related interstitial lung disease (ILD). RESULTS: The appearance of fibrocytes in the lungs of TGFß1-transgenic mice required semaphorin 7a. Replacement of semaphorin 7a on bone marrow-derived cells restored lung fibrosis and fibrocytes. Immunoneutralization of ß1 integrin reduced pulmonary fibrocytes and fibrosis. Peripheral blood mononuclear cells (PBMCs) from patients with scleroderma-related ILD showed increased levels of messenger RNA for semaphorin 7a and its receptors, with semaphorin 7a located on collagen-producing fibrocytes and CD19+ lymphocytes. Peripheral blood fibrocyte outgrowth was enhanced in these patients. Stimulation of normal human PBMCs with recombinant semaphorin 7a enhanced fibrocyte differentiation; these effects were attenuated by ß1 integrin neutralization. CONCLUSION: Our findings indicate that interventions that reduce semaphorin 7a expression or prevent the semaphorin 7a-ß1 integrin interaction may ameliorate TGFß1-driven or fibrocyte-associated autoimmune fibroses.

U2.3 Precursor Small Nuclear RNA in vitro Processing Assay.

Small nuclear RNAs (snRNAs) are vital for eukaryotic cell activities and play important roles in pre-mRNA splicing. The molecular mechanism underlying the transcription of snRNA, regulated via upstream/downstream cis-elements and relevant trans-elements, has been investigated in detail using cell-free extracts. However, the processing of precursor snRNA (pre-snRNA), which is required by 3' end maturation of pre-snRNA, remains unclear as a proper processing assay is difficult to develop in vitro. Here, we present an in vitro method using synthetic labeled RNA as substrates to study the 3' cleavage of pre-snRNA.

Macrophage-derived netrin-1 drives adrenergic nerve-associated lung fibrosis.

Fibrosis is a macrophage-driven process of uncontrolled extracellular matrix accumulation. Neuronal guidance proteins such as netrin-1 promote inflammatory scarring. We found that macrophage-derived netrin-1 stimulates fibrosis through its neuronal guidance functions. In mice, fibrosis due to inhaled bleomycin engendered netrin-1-expressing macrophages and fibroblasts, remodeled adrenergic nerves, and augmented noradrenaline. Cell-specific knockout mice showed that collagen accumulation, fibrotic histology, and nerve-associated endpoints required netrin-1 of macrophage but not fibroblast origin. Adrenergic denervation; haploinsufficiency of netrin-1's receptor, deleted in colorectal carcinoma; and therapeutic α1 adrenoreceptor antagonism improved collagen content and histology. An idiopathic pulmonary fibrosis (IPF) lung microarray data set showed increased netrin-1 expression. IPF lung tissues were enriched for netrin-1+ macrophages and noradrenaline. A longitudinal IPF cohort showed improved survival in patients prescribed α1 adrenoreceptor blockade. This work showed that macrophages stimulate lung fibrosis via netrin-1-driven adrenergic processes and introduced α1 blockers as a potentially new fibrotic therapy.

Circulating monocytes from systemic sclerosis patients with interstitial lung disease show an enhanced profibrotic phenotype.

Profibrotic cells derived from circulating CD14+ monocytes include fibrocytes and alternatively activated macrophages. These cells are associated with interstitial lung disease (ILD) and are implicated in the pathogenesis of systemic sclerosis (SSc); however, the simultaneous presence of profibrotic cells and their associated mediators in the circulation of these patients has not been defined. We hypothesized that monocytes from patients with SSc-related ILD (SSc-ILD) would show profibrotic characteristics when compared with normal controls. We recruited patients with SSc-ILD (n=12) and normal controls (n=27) and quantified circulating collagen-producing cells by flow cytometry for CD45 and pro-collagen I. The in vitro activation potential of CD14+ monocytes in response to lipopolysaccharide was assessed using flow cytometry for CD163, and by ELISA for CCL18 and IL-10 secretion. Profibrotic mediators in plasma were quantified using Luminex-based assays. The concentration of circulating collagen-producing cells was increased in the SSc-ILD patients when compared with controls. These cells were composed of both CD34+ fibrocytes and a population of CD34+CD14+ cells. Cultured CD14+ monocytes from SSc-ILD patients revealed a profibrotic phenotype characterized by expression of CD163 and by enhanced secretion of CCL18 and IL-10 in response to proinflammatory activation. Plasma levels of IL-10, MCP-1, IL-1RA, and TNF levels were significantly elevated in the plasma of the SSc-ILD cohort. Subgroup analysis of the normal controls revealed that unlike the subjects < or =35 years, subjects > or =60 years old showed higher levels of circulating CD34+CD14+ cells, collagen-producing CD14+ monocytes, CD163+ monocytes, IL-4, IL-10, IL-13, MCP-1, and CCL18. These data indicate that the blood of patients with SSc-ILD and of healthy aged controls is enriched for fibrocytes, profibrotic monocytes, and fibrosis-associated mediators. Investigations defining the factors responsible for this peripheral blood profile may provide new insight into SSc-ILD as well as the pathophysiology of aging.

Chitinase 1 regulates pulmonary fibrosis by modulating TGF-ß/SMAD7 pathway via TGFBRAP1 and FOXO3.

TGF-ß1 is a critical mediator of tissue fibrosis in health and disease whose effects are augmented by chitinase 1 (CHIT1). However, the mechanisms that CHIT1 uses to regulate TGF-ß1-mediated fibrotic responses have not been defined. Here, we demonstrate that CHIT1 enhances TGF-ß1-stimulated fibrotic cellular and tissue responses and TGF-ß1 signaling. Importantly, we also demonstrate that these effects are mediated by the ability of CHIT1 to inhibit TGF-ß1 induction of its feedback inhibitor, SMAD7. CHIT1 also interacted with TGF-ß receptor associated protein 1 (TGFBRAP1) and forkhead box O3 (FOXO3) with TGFBRAP1 playing a critical role in CHIT1 enhancement of TGF-ß1 signaling and effector responses and FOXO3 playing a critical role in TGF-ß1 induction of SMAD7. These pathways were disease relevant because the levels of CHIT1 were increased and inversely correlated with SMAD7 in tissues from patients with idiopathic pulmonary fibrosis or scleroderma-associated interstitial lung disease. These studies demonstrate that CHIT1 regulates TGF-ß1/SMAD7 axis via TGFBRAP1 and FOXO3 and highlight the importance of these pathways in the pathogenesis of pulmonary fibrosis.

Human pericytes adopt myofibroblast properties in the microenvironment of the IPF lung.

Idiopathic pulmonary fibrosis (IPF) is a fatal disease of unknown etiology characterized by a compositionally and mechanically altered extracellular matrix. Poor understanding of the origin of α-smooth muscle actin (α-SMA) expressing myofibroblasts has hindered curative therapies. Though proposed as a source of myofibroblasts in mammalian tissues, identification of microvascular pericytes (PC) as contributors to α-SMA-expressing populations in human IPF and the mechanisms driving this accumulation remain unexplored. Here, we demonstrate enhanced detection of α-SMA+ cells coexpressing the PC marker neural/glial antigen 2 in the human IPF lung. Isolated human PC cultured on decellularized IPF lung matrices adopt expression of α-SMA, demonstrating that these cells undergo phenotypic transition in response to direct contact with the extracellular matrix (ECM) of the fibrotic human lung. Using potentially novel human lung-conjugated hydrogels with tunable mechanical properties, we decoupled PC responses to matrix composition and stiffness to show that α-SMA+ PC accumulate in a mechanosensitive manner independent of matrix composition. PC activated with TGF-ß1 remodel the normal lung matrix, increasing tissue stiffness to facilitate the emergence of α-SMA+ PC via MKL-1/MTRFA mechanotranduction. Nintedanib, a tyrosine-kinase inhibitor approved for IPF treatment, restores the elastic modulus of fibrotic lung matrices to reverse the α-SMA+ phenotype. This work furthers our understanding of the role that microvascular PC play in the evolution of IPF, describes the creation of an ex vivo platform that advances the study of fibrosis, and presents a potentially novel mode of action for a commonly used antifibrotic therapy that has great relevance for human disease.

Antifibrotic role of vascular endothelial growth factor in pulmonary fibrosis.

The chronic progressive decline in lung function observed in idiopathic pulmonary fibrosis (IPF) appears to result from persistent nonresolving injury to the epithelium, impaired restitution of the epithelial barrier in the lung, and enhanced fibroblast activation. Thus, understanding these key mechanisms and pathways modulating both is essential to greater understanding of IPF pathogenesis. We examined the association of VEGF with the IPF disease state and preclinical models in vivo and in vitro. Tissue and circulating levels of VEGF were significantly reduced in patients with IPF, particularly in those with a rapidly progressive phenotype, compared with healthy controls. Lung-specific overexpression of VEGF significantly protected mice following intratracheal bleomycin challenge, with a decrease in fibrosis and bleomycin-induced cell death observed in the VEGF transgenic mice. In vitro, apoptotic endothelial cell-derived mediators enhanced epithelial cell injury and reduced epithelial wound closure. This process was rescued by VEGF pretreatment of the endothelial cells via a mechanism involving thrombospondin-1 (TSP1). Taken together, these data indicate beneficial roles for VEGF during lung fibrosis via modulating epithelial homeostasis through a previously unrecognized mechanism involving the endothelium.