RESUMEN
The NLRP3 inflammasome is linked to sterile and pathogen-dependent inflammation, and its dysregulation underlies many chronic diseases. Mitochondria have been implicated as regulators of the NLRP3 inflammasome through several mechanisms including generation of mitochondrial reactive oxygen species (ROS). Here, we report that mitochondrial electron transport chain (ETC) complex I, II, III and V inhibitors all prevent NLRP3 inflammasome activation. Ectopic expression of Saccharomyces cerevisiae NADH dehydrogenase (NDI1) or Ciona intestinalis alternative oxidase, which can complement the functional loss of mitochondrial complex I or III, respectively, without generation of ROS, rescued NLRP3 inflammasome activation in the absence of endogenous mitochondrial complex I or complex III function. Metabolomics revealed phosphocreatine (PCr), which can sustain ATP levels, as a common metabolite that is diminished by mitochondrial ETC inhibitors. PCr depletion decreased ATP levels and NLRP3 inflammasome activation. Thus, the mitochondrial ETC sustains NLRP3 inflammasome activation through PCr-dependent generation of ATP, but via a ROS-independent mechanism.
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Inflamasomas , Proteína con Dominio Pirina 3 de la Familia NLR , Adenosina Trifosfato/metabolismo , Transporte de Electrón , Inflamasomas/metabolismo , Proteína con Dominio Pirina 3 de la Familia NLR/genética , Proteína con Dominio Pirina 3 de la Familia NLR/metabolismo , Especies Reactivas de Oxígeno/metabolismoRESUMEN
Viral infection causes the host to activate an antiviral response that, in part, is dependent on mitochondrial antiviral signaling protein (MAVS) to stimulate type I interferons. Zhang et al. (2019) demonstrate that glucose-generated lactate interacts with MAVS to suppress type I interferons. This study links glucose metabolism to antiviral responses.
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Proteínas Adaptadoras Transductoras de Señales , Antivirales , Línea Celular , Glucosa , Ácido LácticoRESUMEN
The product of hexokinase (HK) enzymes, glucose-6-phosphate, can be metabolized through glycolysis or directed to alternative metabolic routes, such as the pentose phosphate pathway (PPP) to generate anabolic intermediates. HK1 contains an N-terminal mitochondrial binding domain (MBD), but its physiologic significance remains unclear. To elucidate the effect of HK1 mitochondrial dissociation on cellular metabolism, we generated mice lacking the HK1 MBD (ΔE1HK1). These mice produced a hyper-inflammatory response when challenged with lipopolysaccharide. Additionally, there was decreased glucose flux below the level of GAPDH and increased upstream flux through the PPP. The glycolytic block below GAPDH is mediated by the binding of cytosolic HK1 with S100A8/A9, resulting in GAPDH nitrosylation through iNOS. Additionally, human and mouse macrophages from conditions of low-grade inflammation, such as aging and diabetes, displayed increased cytosolic HK1 and reduced GAPDH activity. Our data indicate that HK1 mitochondrial binding alters glucose metabolism through regulation of GAPDH.
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Glucosa , Hexoquinasa/metabolismo , Animales , Glucosa/metabolismo , Glucólisis , Hexoquinasa/genética , Ratones , Mitocondrias/metabolismo , Vía de Pentosa FosfatoRESUMEN
GM-CSF has been portrayed as a critical cytokine in the pathogenesis of experimental autoimmune encephalomyelitis (EAE) and, ostensibly, in multiple sclerosis. C57BL/6 mice deficient in GM-CSF are resistant to EAE induced by immunization with myelin oligodendrocyte glycoprotein (MOG)35-55 The mechanism of action of GM-CSF in EAE is poorly understood. In this study, we show that GM-CSF augments the accumulation of MOG35-55-specific T cells in the skin draining lymph nodes of primed mice, but it is not required for the development of encephalitogenic T cells. Abrogation of GM-CSF receptor signaling in adoptive transfer recipients of MOG35-55-specific T cells did not alter the incidence of EAE or the trajectory of its initial clinical course, but it limited the extent of chronic CNS tissue damage and neurologic disability. The attenuated clinical course was associated with a relative dearth of MOG35-55-specific T cells, myeloid dendritic cells, and neutrophils, as well as an abundance of B cells, within CNS infiltrates. Our data indicate that GM-CSF drives chronic tissue damage and disability in EAE via pleiotropic pathways, but it is dispensable during early lesion formation and the onset of neurologic deficits.
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Linfocitos T CD4-Positivos/inmunología , Sistema Nervioso Central/citología , Sistema Nervioso Central/patología , Encefalomielitis Autoinmune Experimental/patología , Factor Estimulante de Colonias de Granulocitos y Macrófagos/inmunología , Glicoproteína Mielina-Oligodendrócito/inmunología , Traslado Adoptivo , Animales , Linfocitos B/inmunología , Linfocitos T CD4-Positivos/trasplante , Células Dendríticas/inmunología , Encefalomielitis Autoinmune Experimental/inmunología , Factor Estimulante de Colonias de Granulocitos y Macrófagos/genética , Pulmón/patología , Ganglios Linfáticos/citología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Glicoproteína Mielina-Oligodendrócito/administración & dosificación , Neutrófilos/inmunología , Fragmentos de Péptidos/administración & dosificación , Fragmentos de Péptidos/inmunología , Receptores de Factor Estimulante de Colonias de Granulocitos y Macrófagos/genética , Receptores de Factor Estimulante de Colonias de Granulocitos y Macrófagos/metabolismoRESUMEN
BACKGROUND: Myelin oligodendrocyte glycoprotein (MOG)-reactive T-helper (Th)1 cells induce conventional experimental autoimmune encephalomyelitis (cEAE), characterized by ascending paralysis and monocyte-predominant spinal cord infiltrates, in C57BL/6 wildtype (WT) hosts. The same T cells induce an atypical form of EAE (aEAE), characterized by ataxia and neutrophil-predominant brainstem infiltrates, in syngeneic IFNγ receptor (IFNγR)-deficient hosts. Production of ELR+ CXC chemokines within the CNS is required for the development of aEAE, but not cEAE. The cellular source(s) and localization of ELR+ CXC chemokines in the CNS and the IFNγ-dependent pathways that regulate their production remain to be elucidated. METHODS: The spatial distribution of inflammatory lesions and CNS expression of the ELR+ CXC chemokines, CXCL1 and CXCL2, were determined via immunohistochemistry and/or in situ hybridization. Levels of CXCL1 and CXCL2, and their cognate receptor CXCR2, were measured in/on leukocyte subsets by flow cytometric and quantitative PCR (qPCR) analysis. Bone marrow neutrophils and macrophages were cultured with inflammatory stimuli in vitro prior to measurement of CXCL2 and CXCR2 by qPCR or flow cytometry. RESULTS: CNS-infiltrating neutrophils and monocytes, and resident microglia, are a prominent source of CXCL2 in the brainstem of IFNγRKO adoptive transfer recipients during aEAE. In WT transfer recipients, IFNγ directly suppresses CXCL2 transcription in microglia and myeloid cells, and CXCR2 transcription in CNS-infiltrating neutrophils. Consequently, infiltration of the brainstem parenchyma from the adjacent meninges is blocked during cEAE. CXCL2 directly stimulates its own expression in cultured neutrophils, which is enhanced by IL-1 and suppressed by IFNγ. CONCLUSIONS: We provide evidence for an IFNγ-regulated CXCR2/CXCL2 autocrine/paracrine feedback loop in innate immune cells that determines the location of CNS infiltrates during Th1-mediated EAE. When IFNγ signaling is impaired, myeloid cell production of CXCL2 increases, which promotes brainstem inflammation and results in clinical ataxia. IFNγ, produced within the CNS of WT recipients, suppresses myeloid cell CXCR2 and CXCL2 production, thereby skewing the location of neuroinflammatory infiltrates to the spinal cord and the clinical phenotype to an ascending paralysis. These data reveal a novel mechanism by which IFNγ and CXCL2 interact to direct regional recruitment of leukocytes in the CNS, resulting in distinct clinical presentations.
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Encéfalo/metabolismo , Quimiocina CXCL2/metabolismo , Encefalomielitis Autoinmune Experimental/patología , Interferón gamma/metabolismo , Transducción de Señal/fisiología , Animales , Encéfalo/patología , Modelos Animales de Enfermedad , Encefalomielitis Autoinmune Experimental/inducido químicamente , Proteína Ácida Fibrilar de la Glía/metabolismo , Interferón gamma/genética , Interferón gamma/farmacología , Antígenos Comunes de Leucocito/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Monocitos/efectos de los fármacos , Monocitos/patología , Glicoproteína Mielina-Oligodendrócito/toxicidad , Células Mieloides/efectos de los fármacos , Infiltración Neutrófila/efectos de los fármacos , Neutrófilos/patología , Tejido Parenquimatoso/patología , Fragmentos de Péptidos/toxicidad , ARN Mensajero/metabolismo , Transducción de Señal/efectos de los fármacosRESUMEN
The adoptive transfer of myelin-reactive T cells into wild-type hosts results in spinal cord inflammation and ascending paralysis, referred to as conventional experimental autoimmune encephalomyelitis (EAE), as opposed to brainstem inflammation and ataxia, which characterize disease in IFN-γRKO hosts (atypical EAE). In this article, we show that atypical EAE correlates with preferential upregulation of CXCL2 in the brainstem, and is driven by CXCR2-dependent recruitment of neutrophils. In contrast, conventional EAE is associated with upregulation of CCL2 in the spinal cord, and is driven by recruitment of monocytes via a partially CCR2-dependent pathway. This study illustrates how regional differences in chemokine expression within a target organ shape the spatial pattern and composition of autoimmune infiltrates, leading to disparate clinical outcomes.
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Sistema Nervioso Central/inmunología , Quimiocinas/inmunología , Encefalomielitis Autoinmune Experimental/inmunología , Inflamación/inmunología , Animales , Antígenos CD/inmunología , Antígenos CD/metabolismo , Antígenos de Diferenciación de Linfocitos T/inmunología , Antígenos de Diferenciación de Linfocitos T/metabolismo , Tronco Encefálico/inmunología , Tronco Encefálico/metabolismo , Tronco Encefálico/patología , Linfocitos T CD4-Positivos/inmunología , Linfocitos T CD4-Positivos/metabolismo , Sistema Nervioso Central/metabolismo , Sistema Nervioso Central/patología , Quimiocinas/biosíntesis , Enfermedades Desmielinizantes/genética , Enfermedades Desmielinizantes/inmunología , Enfermedades Desmielinizantes/metabolismo , Encefalomielitis Autoinmune Experimental/genética , Encefalomielitis Autoinmune Experimental/metabolismo , Citometría de Flujo , Inmunofenotipificación , Inflamación/genética , Inflamación/metabolismo , Interleucina-12/inmunología , Interleucina-12/metabolismo , Interleucina-17/inmunología , Interleucina-17/metabolismo , Subunidad alfa del Receptor de Interleucina-2/inmunología , Subunidad alfa del Receptor de Interleucina-2/metabolismo , Lectinas Tipo C/inmunología , Lectinas Tipo C/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Microscopía Confocal , Monocitos/inmunología , Monocitos/metabolismo , Glicoproteína Mielina-Oligodendrócito , Neutrófilos/inmunología , Neutrófilos/metabolismo , Fragmentos de Péptidos , Receptores CCR2/deficiencia , Receptores CCR2/genética , Receptores CCR2/inmunología , Receptores de Interferón/deficiencia , Receptores de Interferón/genética , Receptores de Interferón/inmunología , Receptores de Interleucina-8B/inmunología , Receptores de Interleucina-8B/metabolismo , Receptor de Interferón gammaRESUMEN
Microglia are necessary for central nervous system (CNS) function during development and play roles in ageing, Alzheimer's disease and the response to demyelinating injury1-5. The mitochondrial respiratory chain (RC) is necessary for conventional T cell proliferation6 and macrophage-dependent immune responses7-10. However, whether mitochondrial RC is essential for microglia proliferation or function is not known. We conditionally deleted the mitochondrial complex III subunit Uqcrfs1 (Rieske iron-sulfur polypeptide 1) in the microglia of adult mice to assess the requirement of microglial RC for survival, proliferation and adult CNS function in vivo. Notably, mitochondrial RC function was not required for survival or proliferation of microglia in vivo. RNA sequencing analysis showed that loss of RC function in microglia caused changes in gene expression distinct from aged or disease-associated microglia. Microglia-specific loss of mitochondrial RC function is not sufficient to induce cognitive decline. Amyloid-ß plaque coverage decreased and microglial interaction with amyloid-ß plaques increased in the hippocampus of 5xFAD mice with mitochondrial RC-deficient microglia. Microglia-specific loss of mitochondrial RC function did impair remyelination following an acute, reversible demyelinating event. Thus, mitochondrial respiration in microglia is dispensable for proliferation but is essential to maintain a proper response to CNS demyelinating injury.
RESUMEN
Apolipoprotein E (ApoE) is recognized for its pleiotropic properties that suppress inflammation. We report that ApoE serves as a metabolic rheostat that regulates microRNA control of glycolytic and mitochondrial activity in myeloid cells and hematopoietic stem and progenitor cells (HSPCs). ApoE expression in myeloid cells increases microRNA-146a, which reduces nuclear factor κB (NF-κB)-driven GLUT1 expression and glycolytic activity. In contrast, ApoE expression reduces microRNA-142a, which increases carnitine palmitoyltransferase 1a (CPT1A) expression, fatty acid oxidation, and oxidative phosphorylation. Improved mitochondrial metabolism by ApoE expression causes an enrichment of tricarboxylic acid (TCA) cycle metabolites and nicotinamide adenine dinucleotide (NAD+) in macrophages. The study of mice with conditional ApoE expression supports the capacity of ApoE to foster microRNA-controlled immunometabolism. Modulation of microRNA-146a and -142a in the hematopoietic system of hyperlipidemic mice using RNA mimics and antagonists, respectively, improves mitochondrial metabolism, which suppresses inflammation and hematopoiesis. Our findings unveil microRNA regulatory circuits, controlled by ApoE, that exert metabolic control over hematopoiesis and inflammation in hyperlipidemia.
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Hiperlipidemias , Enfermedades Metabólicas , MicroARNs , Ratones , Animales , Hiperlipidemias/genética , Hiperlipidemias/metabolismo , Inflamación/metabolismo , MicroARNs/genética , MicroARNs/metabolismo , Hematopoyesis , Apolipoproteínas E/genéticaRESUMEN
Aging in mammals leads to reduction in genes encoding the 45-subunit mitochondrial electron transport chain complex I. It has been hypothesized that normal aging and age-related diseases such as Parkinson's disease are in part due to modest decrease in expression of mitochondrial complex I subunits. By contrast, diminishing expression of mitochondrial complex I genes in lower organisms increases lifespan. Furthermore, metformin, a putative complex I inhibitor, increases healthspan in mice and humans. In the present study, we investigated whether loss of one allele of Ndufs2, the catalytic subunit of mitochondrial complex I, impacts healthspan and lifespan in mice. Our results indicate that Ndufs2 hemizygous mice (Ndufs2+/-) show no overt impairment in aging-related motor function, learning, tissue histology, organismal metabolism, or sensitivity to metformin in a C57BL6/J background. Despite a significant reduction of Ndufs2 mRNA, the mice do not demonstrate a significant decrease in complex I function. However, there are detectable transcriptomic changes in individual cell types and tissues due to loss of one allele of Ndufs2. Our data indicate that a 50% decline in mRNA of the core mitochondrial complex I subunit Ndufs2 is neither beneficial nor detrimental to healthspan.
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Metformina , NADH Deshidrogenasa , Animales , Complejo I de Transporte de Electrón/genética , Complejo I de Transporte de Electrón/metabolismo , Mamíferos/metabolismo , Metformina/metabolismo , Ratones , Ratones Endogámicos C57BL , Mitocondrias/genética , Mitocondrias/metabolismo , NADH Deshidrogenasa/genética , NADH Deshidrogenasa/metabolismo , ARN Mensajero/genética , ARN Mensajero/metabolismoRESUMEN
Although γherpesvirus infections are associated with enhanced lung fibrosis in both clinical and animal studies, there is limited understanding about fibrotic effects of γherpesviruses on cell types present in the lung, particularly during latent infection. Wild-type mice were intranasally infected with a murine γherpesvirus (γHV-68) or mock-infected with saline. Twenty-eight days postinfection (dpi), â¼14 days following clearance of the lytic infection, alveolar macrophages (AMs), mesenchymal cells, and CD19-enriched cell populations from the lung and spleen express M(3) and/or glycoprotein B (gB) viral mRNA and harbor viral genome. AMs from infected mice express more transforming growth factor (TGF)-ß(1), CCL2, CCL12, TNF-α, and IFN-γ than AMs from mock-infected mice. Mesenchymal cells express more total TGF-ß(1), CCL12, and TNF-α than mesenchymal cells from mock-infected mice. Lung and spleen CD19-enriched cells express more total TGF-ß(1) 28 dpi compared with controls. The CD19-negative fraction of the spleen overexpresses TGF-ß(1) and harbors viral genome, but this likely represents infection of monocytes. Purified T cells from the lung harbor almost no viral genome. Purified T cells overexpress IL-10 but not TGF-ß(1). Intracellular cytokine staining demonstrated that lung T cells at 28 dpi produce IFN-γ but not IL-4. Thus infection with a murine γherpesvirus is sufficient to upregulate profibrotic and proinflammatory factors in a variety of lung resident and circulating cell types 28 dpi. Our results provide new information about possible contributions of these cells to fibrogenesis in the lungs of individuals harboring a γherpesvirus infection and may help explain why γHV-68 infection can augment or exacerbate fibrotic responses in mice.
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Citocinas/biosíntesis , Infecciones por Herpesviridae/inmunología , Fibrosis Pulmonar/etiología , Rhadinovirus/patogenicidad , Infecciones Tumorales por Virus/inmunología , Animales , Secuencia de Bases , Quimiocina CCL2/biosíntesis , Cartilla de ADN/genética , ADN Viral/genética , Modelos Animales de Enfermedad , Infecciones por Herpesviridae/genética , Infecciones por Herpesviridae/virología , Interferón gamma/biosíntesis , Interleucina-10/biosíntesis , Pulmón/inmunología , Pulmón/virología , Activación de Macrófagos , Macrófagos Alveolares/inmunología , Macrófagos Alveolares/virología , Masculino , Mesodermo/inmunología , Mesodermo/virología , Ratones , Ratones Endogámicos C57BL , Proteínas Quimioatrayentes de Monocitos/biosíntesis , Fibrosis Pulmonar/genética , Fibrosis Pulmonar/inmunología , Fibrosis Pulmonar/virología , Bazo/inmunología , Bazo/virología , Linfocitos T/inmunología , Linfocitos T/virología , Factor de Crecimiento Transformador beta1/biosíntesis , Factor de Necrosis Tumoral alfa/biosíntesis , Infecciones Tumorales por Virus/genética , Infecciones Tumorales por Virus/virología , Carga ViralRESUMEN
Glioblastoma is characterized by the robust infiltration of immunosuppressive tumor-associated myeloid cells (TAMCs). It is not fully understood how TAMCs survive in the acidic tumor microenvironment to cause immunosuppression in glioblastoma. Metabolic and RNA-seq analysis of TAMCs revealed that the arginine-ornithine-polyamine axis is up-regulated in glioblastoma TAMCs but not in tumor-infiltrating CD8+ T cells. Active de novo synthesis of highly basic polyamines within TAMCs efficiently buffered low intracellular pH to support the survival of these immunosuppressive cells in the harsh acidic environment of solid tumors. Administration of difluoromethylornithine (DFMO), a clinically approved inhibitor of polyamine generation, enhanced animal survival in immunocompetent mice by causing a tumor-specific reduction of polyamines and decreased intracellular pH in TAMCs. DFMO combination with immunotherapy or radiotherapy further enhanced animal survival. These findings indicate that polyamines are used by glioblastoma TAMCs to maintain normal intracellular pH and cell survival and thus promote immunosuppression during tumor evolution.
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Glioblastoma , Animales , Linfocitos T CD8-positivos/metabolismo , Supervivencia Celular , Eflornitina/metabolismo , Eflornitina/farmacología , Glioblastoma/metabolismo , Concentración de Iones de Hidrógeno , Terapia de Inmunosupresión , Ratones , Células Mieloides/metabolismo , Poliaminas/metabolismo , Microambiente TumoralRESUMEN
Lymphocyte homing into the intestine is mediated by binding of leukocytes to mucosal addressin cell adhesion molecule 1 (MAdCAM-1), expressed on endothelial cells. Currently, the immune system of the gut is considered a major modulator not only of inflammatory bowel disease, but also of extra-intestinal autoimmune disorders, including multiple sclerosis (MS). Despite intense research in this field, the exact role of the intestine in the pathogenesis of (neuro-)inflammatory disease conditions remains to be clarified. This prompted us to investigate the role of MAdCAM-1 in immunological processes in the intestine during T cell-mediated autoimmunity of the central nervous system (CNS). Using the experimental autoimmune encephalomyelitis model of MS, we show that MAdCAM-1-deficient (MAdCAM-1-KO) mice are less susceptible to actively MOG35-55-induced disease. Protection from disease was accompanied by decreased numbers of immune cells in the lamina propria and Peyer's patches as well as reduced immune cell infiltration into the spinal cord. MOG35-55-recall responses were intact in other secondary lymphoid organs of MAdCAM-1-KO mice. The composition of specific bacterial groups within the microbiome did not differ between MAdCAM-1-KO mice and controls, while MAdCAM-1-deficiency severely impaired migration of MOG35-55-activated lymphocytes to the gut. Our data indicate a critical role of MAdCAM-1 in the development of CNS inflammation by regulating lymphocyte homing to the intestine, and may suggest a role for the intestinal tract in educating lymphocytes to become encephalitogenic.
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Moléculas de Adhesión Celular/inmunología , Encefalomielitis Autoinmune Experimental/inmunología , Mucoproteínas/inmunología , Linfocitos T/inmunología , Animales , Movimiento Celular/inmunología , Sistema Nervioso Central/inmunología , Células Endoteliales/inmunología , Enfermedades Inflamatorias del Intestino/inmunología , Mucosa Intestinal/inmunología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Microbiota/inmunología , Esclerosis Múltiple , Ganglios Linfáticos Agregados/inmunología , Receptores Mensajeros de Linfocitos/inmunologíaRESUMEN
BACKGROUND: We have shown previously that murine gammaherpesvirus 68 (γHV68) infection exacerbates established pulmonary fibrosis. Because Toll-like receptor (TLR)-9 may be important in controlling the immune response to γHV68 infection, we examined how TLR-9 signaling effects exacerbation of fibrosis in response to viral infection, using models of bleomycin- and fluorescein isothiocyanate-induced pulmonary fibrosis in wild-type (Balb/c) and TLR-9-/- mice. RESULTS: We found that in the absence of TLR-9 signaling, there was a significant increase in collagen deposition following viral exacerbation of fibrosis. This was not associated with increased viral load in TLR-9-/- mice or with major alterations in T helper (Th)1 and Th2 cytokines. We examined alveolar epithelial-cell apoptosis in both strains, but this could not explain the altered fibrotic outcomes. As expected, TLR-9-/- mice had a defect in the production of interferon (IFN)-ß after viral infection. Balb/c fibroblasts infected with γHV68 in vitro produced more IFN-ß than did infected TLR-9-/- fibroblasts. Accordingly, in vitro infection of Balb/c fibroblasts resulted in reduced proliferation rates whereas infection of TLR-9-/- fibroblasts did not. Finally, therapeutic administration of CpG oligodeoxynucleotides ameliorated bleomycin-induced fibrosis in wild-type mice. CONCLUSIONS: These results show a protective role for TLR-9 signaling in murine models of lung fibrosis, and highlight differences in the biology of TLR-9 between mice and humans.
RESUMEN
Plasminogen activation to plasmin protects from lung fibrosis, but the mechanism underlying this antifibrotic effect remains unclear. We found that mice lacking plasminogen activation inhibitor-1 (PAI-1), which are protected from bleomycin-induced pulmonary fibrosis, exhibit lung overproduction of the antifibrotic lipid mediator prostaglandin E2 (PGE2). Plasminogen activation upregulated PGE2 synthesis in alveolar epithelial cells, lung fibroblasts, and lung fibrocytes from saline- and bleomycin-treated mice, as well as in normal fetal and adult primary human lung fibroblasts. This response was exaggerated in cells from Pai1-/- mice. Although enhanced PGE2 formation required the generation of plasmin, it was independent of proteinase-activated receptor 1 (PAR-1) and instead reflected proteolytic activation and release of HGF with subsequent induction of COX-2. That the HGF/COX-2/PGE2 axis mediates in vivo protection from fibrosis in Pai1-/- mice was demonstrated by experiments showing that a selective inhibitor of the HGF receptor c-Met increased lung collagen to WT levels while reducing COX-2 protein and PGE2 levels. Of clinical interest, fibroblasts from patients with idiopathic pulmonary fibrosis were found to be defective in their ability to induce COX-2 and, therefore, unable to upregulate PGE2 synthesis in response to plasmin or HGF. These studies demonstrate crosstalk between plasminogen activation and PGE2 generation in the lung and provide a mechanism for the well-known antifibrotic actions of the fibrinolytic pathway.