Following immune reconstitution, hematopoietic stem cell transplant patients often display reduced immune function and are especially susceptible to lung infections. In a mouse model of syngeneic bone marrow transplantation (BMT), we previously reported that PGE2 is overproduced in lungs of BMT mice, significantly impairing host defense against Pseudomonas aeruginosa. This impairment in host defense post-BMT is also marked by diminished alveolar macrophage (AM) phagocytosis, bacterial killing, and production of TNF-α and cysteinyl leukotrienes. However, a mechanism by which overproduction of PGE2 suppresses pulmonary host defense post-BMT is unknown. As IL-1R–associated kinase (IRAK)-M is a known inhibitor of MyD88-dependent IL-1R/TLR signaling and macrophage function, we sought to determine whether IRAK-M is involved in PGE2-induced immunosuppression post-BMT. We found that IRAK-M expression is elevated 3.5-fold in BMT AMs relative to control AMs, and this is related to AM overproduction of PGE2. Furthermore, genetic ablation of IRAK-M in the bone marrow of BMT mice restores host defense against P. aeruginosa. Despite AM overproduction of PGE2 and elevated E prostanoid 2 receptor expression, AM phagocytosis, killing, and production of cysteinyl leukotrienes and TNF-α are restored in the absence of IRAK-M post-BMT. Also, treatment with PGE2 does not inhibit AM phagocytosis in the absence of IRAK-M. These data suggest that the absence of IRAK-M in the hematopoietic compartment post-BMT enhances pulmonary host defense and mitigates AM sensitivity to the inhibitory effects of PGE2. Therefore, strategies to limit IRAK-M elevation post-BMT may be efficacious in reducing patient susceptibility to infection.
Hematopoietic stem cell transplant (HSCT) therapy is limited by pulmonary infections. Mice with fully reconstituted hematopoietic compartments, including alveolar macrophages (AMs), post-bone marrow transplantation (BMT) have impaired host defense against Gram negative Pseudomonas aeruginosa. Impaired innate immunity is related to increased production of prostaglandin E2 (PGE2) by AMs. Cyclooxygenase (COX)-2 is the rate-limiting enzyme for synthesis of PGE2 from arachidonic acid, and COX-2 expression is elevated in AMs post-BMT. We hypothesized epigenetic mechanisms may be responsible for upregulation of COX-2 in AMs. Using bisulfite sequencing, we observed the 5’-untranslated region and exon 1 of the COX-2 gene is hypomethylated in the AMs of BMT mice compared to control. COX-2 expression was increased in primary AMs and in the AM cell line (MHS) following treatment with 5-aza-2-deoxycytidine (a methyltransferase inhibitor). Methylation by SssI methyltransferase of a 702 bp region of the COX-2 promoter including the beginning of exon 1 driving a luciferase reporter silenced luciferase expression. Because transforming growth factor beta (TGF-β1) is elevated in lungs post-BMT, we tested whether TGF-β1 could promote expression of COX-2 in a hypermethylated COX-2 vector, and observed TGF-β1 induced modest expression of COX-2, suggesting an ability to demethylate the promoter. Finally, BMTs performed with marrow from mice expressing a dominant negative form of the TGF-β receptor on CD11c-expressing cells (which includes AMs) demonstrated improved host defense and AM function. Our findings suggest impaired innate immunity and PGE2 elevation post-BMT are due to hypomethylation of the COX-2 gene which is at least partly regulated by TGF-β1.
Young (4 month) and aged (15–18 months) mice were given intranasal saline or γ--herpesvirus-68 infection. After 21 days, aged, but not young mice, showed significant increases in collagen content and fibrosis. There were no differences in viral clearance or inflammatory cells (including fibrocytes) between infected aged and young mice. Enzyme-linked immunosorbent assays showed increased transforming growth factor-β in whole lung homogenates of infected aged mice compared with young mice. When fibroblasts from aged and young mice were infected in vitro, aged, but not young, fibroblasts upregulate alpha-smooth muscle actin and collagen I protein. Infection with virus in vivo also demonstrates increased alpha-smooth muscle actin and collagen I protein and collagen I, collagen III, and fibronectin messenger RNA in aged fibroblasts. Furthermore, evaluation revealed that aged fibroblasts at baseline have increased transforming growth factor-β receptor 1 and 2 levels compared with young fibroblasts and are resistant to apoptosis. Increased responsiveness to transforming growth factor-β was verified by increased collagen III and fibronectin messenger RNA after treatment in vitro with transforming growth factor-β.
Lung; Fibrosis; Herpesvirus; Aging
Hematopoietic stem cell transplant patients are susceptible to infection despite cellular reconstitution. In a murine model of syngeneic bone marrow transplantation (BMT), we previously reported that BMT mice have impaired host defense against Pseudomonas aeruginosa pneumonia due to overproduction of (PG)E2 in lung. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is an effector in the PGE2 signaling pathway that negatively regulates alveolar macrophage (AM) phagocytosis and bacterial killing. Therefore, examined whether overproduction of PGE2 after BMT inhibits AM host defense by up-regulating PTEN phosphatase activity. We found that PTEN activity is elevated in BMT AMs in response to increased PGE2 signaling and that pharmacological inhibition of PTEN activity in BMT AMs fully restores phagocytosis of serum-opsonized P. aeruginosa but only partially restores phagocytosis of nonopsonized P. aeruginosa. In wild-type mice transplanted with myeloid-specific conditional PTEN knockout (PTEN CKO) bone marrow, bacterial clearance is improved after challenge with P. aeruginosa pneumonia. Furthermore, PTEN CKO BMT AMs display improved TNF-α production and enhanced phagocytosis and killing of serum-opsonized P. aeruginosa despite overproduction of PGE2. However, AM phagocytosis of nonopsonized P. aeruginosa is only partially restored in the absence of PTEN after BMT. This may be related to elevated AM expression of IL-1 receptor–associated kinase (IRAK)-M, a molecule previously identified in the PGE2 signaling pathway to inhibit AM phagocytosis of nonopsonized bacteria. These data suggest that PGE2 signaling up-regulates IRAK-M independently of PTEN and that these molecules differentially inhibit opsonized and nonopsonized phagocytosis of P. aeruginosa.
pneumonia; lung; neutrophil; eicosanoids; bacteria
Patients receiving hematopoietic stem cell transplantation or bone marrow transplantation (BMT) as therapy for various malignancies or autoimmune diseases have an increased risk for infectious complications posttransplant, especially in the lung. We have used BMT in mice and murine gammaherpesvirus, γHV-68, to study the efficacy of adaptive immune responses post-BMT. Five weeks posttransplant, mice have fully reconstituted their hematopoietic lineages in both the lung and periphery. When challenged with virus, however, BMT mice have a reduced ability to clear lytic virus from the lung. Defective viral control in BMT mice is not related to impaired leukocyte recruitment or defective APC function. Rather, BMT mice are characterized by defective CD4 cell proliferation, skewing of effector CD4 T cells from a Th1 to a Th17 phenotype, and an immunosuppressive lung environment at the time of infection that includes overexpression of TGF-β1 and PGE2 and increased numbers of regulatory T cells. Neither indomethacin treatment to block PG synthesis nor anti-CD25 depletion of regulatory T cells improved antiviral host defense post-BMT. Transplanting mice with transgenic bone marrow expressing a dominant-negative TGF-βRII under the permissive CD4 promoter created mice in which effector CD4 and CD8 cells were unresponsive to TGF-β1. Mice with TGF-β1–nonresponsive effector T cells had restored antiviral immunity and improved Th1 responses post-BMT. Thus, our results indicate that over-expression of TGF-β1 following myeloablative conditioning post-BMT results in impaired effector T cell responses to viral infection.
The authors compared efficiency of alveolar macrophage (AM) reconstitution from donor bone marrow post transplant following 4 chemotherapy conditioning regimens and 2 total body irradiation (TBI) regimens. TBI regimens are more effective in inducing AM reconstitution from donor marrow. However, mice conditioned with 13 Gy split-dose TBI or a dual-chemotherapy regimen (25 mg/kg busulfan × 4 days plus cyclophosphamide 100 mg/kg × 2 days) both demonstrate significant AM repopulation from donor marrow. Additionally, both protocols resulted in impaired pulmonary host defense associated with overproduction of prostaglandin E2 and I2 by AMs and impaired AM phagocytosis post bone marrow transplant.
phagocytosis; prostaglandin; P. aeruginosa
Fibronectin (FN)1, a ubiquitous glycoprotein that plays critical roles in physiologic and pathologic conditions, undergoes alternative splicing which distinguishes plasma FN (pFN) from cellular FN (cFN). Although both pFN and cFN can be incorporated into the extracellular matrix, a distinguishing feature of cFN is the inclusion of an alternatively spliced exon termed EDA (for Extra Type III Domain A). The molecular steps involved in EDA splicing are well-characterized, but pathways influencing EDA splicing are less clear. We have previously found an obligate role for inhibition of the tumor suppressor phosphatase and tensin homologue on chromosome ten (PTEN), the primary regulator of the PI3K/Akt pathway, in fibroblast activation. Here we show TGF-β, a potent inducer of both EDA splicing and fibroblast activation, inhibits PTEN expression and activity in mesenchymal cells, corresponding with enhanced PI3K/Akt signaling. In pten−/− fibroblasts, which resemble activated fibroblasts, inhibition of Akt attenuated FN production and decreased EDA alternative splicing. Moreover, inhibition of mammalian target of rapamycin (mTOR) in pten−/− cells also blocked FN production and EDA splicing. This effect was due to inhibition of Akt-mediated phosphorylation of the primary EDA splicing regulatory protein SF2/ASF. Importantly, FN silencing in pten−/− cells resulted in attenuated proliferation and migration. Thus, our results demonstrate that the PI3K/Akt/mTOR axis is instrumental in FN transcription and alternative splicing, which regulates cell behavior.
Fibronectin; alternative splicing; PTEN; fibrosis; fibroblast; rapamycin
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.
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)-β after viral infection. Balb/c fibroblasts infected with γHV68 in vitro produced more IFN-β 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.
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.
Rationale: No effective treatment exists for idiopathic pulmonary fibrosis, and its pathogenesis remains unclear. Accumulating evidence implicates herpesviruses as cofactors (either initiating or exacerbating agents) of fibrotic lung disease, but a role for latent herpesvirus infection has not been studied.
Objectives: To develop a murine model to determine whether latent herpesvirus infection can augment fibrotic responses and to gain insight into potential mechanisms of enhanced fibrogenesis.
Methods: Mice were infected with murine γherpesvirus 14 to 70 days before a fibrotic challenge with fluorescein isothiocyanate or bleomycin so that the virus was latent at the time of fibrotic challenge. Measurements were made after viral infection alone or after the establishment of fibrosis.
Measurements and Main Results: γHerpesvirus is latent by 14 days post infection, and infection 14 to 70 days before fibrotic challenge augmented fibrosis. Fibrotic augmentation was not dependent on reactivation of the latent virus to a lytic state. Total cell numbers and fibrocyte numbers were increased in the lungs of latently infected mice administered fibrotic challenge compared with mock-infected mice that received fibrotic challenge. Latent infection up-regulates expression of proinflammatory chemokines, transforming growth factor-β1, and cysteinyl leukotrienes in alveolar epithelial cells.
Conclusions: Latent γherpesvirus infection augments subsequent fibrotic responses in mice. Enhanced fibrosis is associated with the induction of profibrotic factors and the recruitment of fibrocytes. Our data complement existing human and animal data supporting the hypothesis that γherpesviruses can serve as initiating cofactors in the pathogenesis of pulmonary fibrosis.
chemokine; epithelial cells; fibrocyte; interstitial lung disease
Rationale: Tissue fibrosis is considered a dysregulated wound-healing response. Fibronectin containing extra type III domain A (EDA) is implicated in the regulation of wound healing. EDA-containing fibronectin is deposited during wound repair, and its presence precedes that of collagen.
Objectives: To investigate the role of EDA-containing fibronectin in lung fibrogenesis.
Methods: Primary lung fibroblasts from patients with idiopathic pulmonary fibrosis or from patients undergoing resection for lung cancer were assessed for EDA-containing fibronectin and α-smooth muscle actin (α-SMA) expression. Mice lacking the EDA domain of fibronectin and their wild-type littermates were challenged with the bleomycin model of lung fibrosis. Primary lung fibroblasts from these mice were assayed in vitro to determine the contribution of EDA-containing fibronectin to fibroblast phenotypes.
Measurements and Main Results: Idiopathic pulmonary fibrosis lung fibroblasts produced markedly more EDA-containing fibronectin and α-SMA than control fibroblasts. EDA-null mice failed to develop significant fibrosis 21 days after bleomycin challenge, whereas wild-type controls developed the expected increase in total lung collagen. Histologic analysis of EDA-null lungs after bleomycin showed less collagen and fewer α-SMA–expressing myofibroblasts compared with that observed in wild-type mice. Failure to develop lung fibrosis in EDA-null mice correlated with diminished activation of latent transforming growth factor (TGF)-β and decreased lung fibroblast responsiveness to active TGF-β in vitro.
Conclusions: The data show that EDA-containing fibronectin is essential for the fibrotic resolution of lung injury through TGF-β activation and responsiveness, and suggest that EDA-containing fibronectin plays a critical role in tissue fibrogenesis.
fibrosis; fibronectin; TGF-β; myofibroblast
We have previously shown that mice that are genetically deficient in the CCR2 gene (CCR2−/− mice) are protected from fluorescein isothiocyanate (FITC)-induced lung fibrosis. Protection from fibrosis correlated with impaired recruitment of fibrocytes (bone marrow–derived cells, which share both leukocyte and mesenchymal markers). There are three ligands for CCR2 in the mouse: CCL2, CCL7, and CCL12. CCL2 and CCL12 are both elevated in the lung after FITC injury, but with different kinetics. CCL2 is maximal at Day 1 and absent by Day 7 after FITC. In contrast, CCL12 peaks at Day 3, but remains elevated through Day 21 after FITC. We now demonstrate that while CCR2−/− mice are protected from FITC-induced fibrosis, CCL2−/− mice are not. CCL2−/− mice are able to recruit fibrocytes to FITC-injured airspaces, unlike CCR2−/− mice. Adoptive transfer of CCR2-expressing fibrocytes augments FITC-induced fibrosis in both wild-type and CCR2−/− mice, suggesting that these cells play a pathogenic role in the disease process. Both CCL2 and CCL12 are chemotactic for fibrocytes. However, neutralization of CCL12 in wild-type mice significantly protects from FITC-induced fibrosis, whereas neutralization of CCL2 was less effective. Thus, CCL12 is likely the CCR2 ligand responsible for driving fibroproliferation in the mouse. As murine CCL12 is homologous to human CCL2, we suggest that the pathobiology of murine CCL12 in fibroproliferation may correlate to human CCL2 biology.
chemokines; fibrocytes; fibrosis; lung