Bortezomib Inhibits Lung Fibrosis and Fibroblast Activation Without Proteasome Inhibition

The FDA-approved proteasomal inhibitor bortezomib (BTZ) has attracted interest for its potential anti-fibrotic actions. However, neither its in vivo efficacy in lung fibrosis nor its dependence on proteasome inhibition has been conclusively defined. In this study, we assessed the therapeutic efficacy of BTZ in a mouse model of pulmonary fibrosis, developed an in vitro protocol to define its actions on diverse fibroblast activation parameters, determined its reliance on proteasome inhibition for these actions in vivo and in vitro and explored alternative mechanisms of action. The therapeutic administration of BTZ diminished the severity of pulmonary fibrosis without reducing proteasome activity in the lung. In experiments designed to mimic this lack of proteasome inhibition in vitro, BTZ reduced fibroblast proliferation, differentiation into myofibroblasts, and collagen synthesis. It promoted de-differentiation of myofibroblasts and overcame their characteristic resistance to apoptosis. Mechanistically, BTZ inhibited kinases important for fibroblast activation while inducing expression of dual-specificity phosphatase 1 or DUSP1, and knockdown of DUSP1 abolished its anti-fibrotic actions in fibroblasts. Collectively, these findings suggest that BTZ exhibits a multidimensional profile of robust inhibitory actions on lung fibroblasts as well as anti-fibrotic actions in vivo. Unexpectedly, these actions appear to be independent of proteasome inhibition, and instead attributable to induction of DUSP1.

Prostaglandin E2 as an inhibitory modulator of fibrogenesis in human lung allografts

RATIONALE

Donor mesenchymal stromal/stem cell (MSC) expansion and fibrotic differentiation is associated with development of bronchiolitis obliterans syndrome (BOS) in human lung allografts. However, the regulators of fibrotic differentiation of these resident mesenchymal cells are not well understood.

OBJECTIVES

This study examines the role of endogenous and exogenous prostaglandin (PG)E2 as a modulator of fibrotic differentiation of human lung allograft-derived MSCs.

METHODS

Effect of PGE2 on proliferation, collagen secretion, and α-smooth muscle actin (α-SMA) expression was assessed in lung-resident MSCs (LR-MSCs) derived from patients with and without BOS. The response pathway involved was elucidated by use of specific agonists and antagonists.

MEASUREMENT AND MAIN RESULTS

PGE2 treatment of LR-MSCs derived from normal lung allografts significantly inhibited their proliferation, collagen secretion, and α-SMA expression. On the basis of pharmacologic and small-interfering RNA approaches, a PGE2/E prostanoid (EP)2/adenylate cyclase pathway was implicated in these suppressive effects. Stimulation of endogenous PGE2 secretion by IL-1β was associated with amelioration of their myofibroblast differentiation in vitro, whereas its inhibition by indomethacin augmented α-SMA expression. LR-MSCs from patients with BOS secreted significantly less PGE2 than non-BOS LR-MSCs. Furthermore, BOS LR-MSCs were found to be defective in their ability to induce cyclooxygenase-2, and therefore unable to up-regulate PGE2 synthesis in response to IL-1β. BOS LR-MSCs also demonstrated resistance to the inhibitory actions of PGE2 in association with a reduction in the EP2/EP1 ratio.

CONCLUSIONS

These data identify the PGE2 axis as an important autocrine-paracrine brake on fibrotic differentiation of LR-MSCs, a failure of which is associated with BOS.

Resident tissue-specific mesenchymal progenitor cells contribute to fibrogenesis in human lung allografts

Fibrotic obliteration of the small airways leading to progressive airflow obstruction, termed bronchiolitis obliterans syndrome (BOS), is the major cause of poor outcomes after lung transplantation. We recently demonstrated that a donor-derived population of multipotent mesenchymal stem cells (MSCs) can be isolated from the bronchoalveolar lavage (BAL) fluid of human lung transplant recipients. Herein, we study the organ specificity of these cells and investigate the role of local mesenchymal progenitors in fibrogenesis after lung transplantation. We demonstrate that human lung allograft-derived MSCs uniquely express embryonic lung mesenchyme-associated transcription factors with a 35,000-fold higher expression of forkhead/winged helix transcription factor forkhead box (FOXF1) noted in lung compared with bone marrow MSCs. Fibrotic differentiation of MSCs isolated from normal lung allografts was noted in the presence of profibrotic mediators associated with BOS, including transforming growth factor-β and IL-13. MSCs isolated from patients with BOS demonstrated increased expression of α-SMA and collagen I when compared with non-BOS controls, consistent with a stable in vivo fibrotic phenotype. FOXF1 mRNA expression in the BAL cell pellet correlated with the number of MSCs in the BAL fluid, and myofibroblasts present in the fibrotic lesions expressed FOXF1 by in situ hybridization. These data suggest a key role for local tissue-specific, organ-resident, mesenchymal precursors in the fibrogenic processes in human adult lungs.

Lung resident mesenchymal stem cells isolated from human lung allografts inhibit T cell proliferation via a soluble mediator

Development of allograft rejection continues to be the major determinant of morbidity and mortality postlung transplantation. We have recently demonstrated that a population of donor-derived mesenchymal stem cells is present in human lung allografts and can be isolated and expanded ex vivo. In this study, we investigated the impact of lung resident mesenchymal stem cells (LR-MSCs), derived from allografts of human lung transplant recipients, on T cell activation in vitro. Similar to bone marrow-derived MSCs, LR-MSCs did not express MHC II or the costimulatory molecules CD80 or CD86. In vitro, LR-MSCs profoundly suppressed the proliferative capacity of T cells in response to a mitogenic or an allogeneic stimulus. The immunosuppressive function of LR-MSCs was also noted in the absence of direct cell contact, indicating that LR-MSCs mediated their effect predominantly via a soluble mediator. LR-MSCs isolated from lung transplant recipients demonstrated PGE(2) secretion at baseline (385 +/- 375 pg/ml), which increased in response to IL-1beta (1149 +/- 1081 pg/ml). The addition of PG synthesis inhibitors (indomethacin and NS-398) substantially abrogated LR-MSC-mediated immunosuppression, indicating that PGE(2) may be one of the major soluble mediators impacting T cell activity. This is the first report to demonstrate that human tissue-derived MSCs isolated from an allogeneic environment have the potential to mediate immunological responses in vitro.

Differential regulation by leukotrienes and calcium of Fc gamma receptor-induced phagocytosis and Syk activation in dendritic cells versus macrophages

Macrophage (MØ) phagocytosis via the Fc receptor for immunoglobulin G (Fc gammaR) requires the spleen tyrosine kinase (Syk) and serves an important antimicrobial function. We have reported previously that Fc gammaR-mediated ingestion and Syk activation in MØ are amplified by and depend on the proinflammatory lipid mediator leukotriene B4 (LTB4). Although Fc gammaR-mediated ingestion is also important for antigen uptake, there is no information about LTB4 regulation of these processes in dendritic cells (DCs). In this study, we compared murine bone marrow (BM)-derived DCs to MØ from BM, peritoneum, and the pulmonary alveolar space. Neither phagocytosis nor Syk activation in DCs was influenced by exogenous LTB4. Unlike the various MØ populations, Syk activation in DCs was likewise unaffected by pharmacologic or genetic strategies to inhibit endogenous LTB4 synthesis or to block the high-affinity LTB4 receptor BLT1. DCs were refractory to regulation by LTB4 despite the fact that they expressed BLT1 and mobilized intracellular calcium in response to its ligation. This resistance to LTB4 in DCs instead reflected the fact that in contrast to MØ, Syk activation in DCs was itself entirely independent of calcium. These results identify a fundamental difference in Fc gammaR signaling between DCs and MØ, which may relate to the divergent, functional consequences of target ingestion in the two cell types.

Characterization of cauliflower mosaic virus (CaMV) resistance in virus-resistant ecotypes of Arabidopsis

Two Arabidopsis ecotypes are resistant to systemic infection by cauliflower mosaic virus (CaMV), a plant para-retrovirus. Arabidopsis ecotype Enkheim-2 (En-2) is highly resistant to CaMV infection while Bla-14 is more weakly resistant. CaMV resistance in En-2 can be largely attributed to the action of a single semidominant gene called cauliflower mosaic virus resistance1 (CAR1), located at a locus on chromosome 1. Resistance in Bla-14 is tightly linked to CAR1 and may be due to a weak allele at the same locus or another gene in a gene cluster. A quantitative polymerase chain reaction assay in conjunction with replication- and movement-incompetent viral mutants was used to determine whether virus replication or movement is affected in the resistant ecotypes. The pattern of accumulation of the wild-type virus in the resistant ecotype, En-2, was similar to that of a movement-incompetent CaMV mutant, suggesting that CAR1 interferes with or fails to support CaMV movement. CaMV-inoculated En-2 plants do not show visible signs of a hypersensitive response. However, indicators of an induced defense response do appear in CaMV-infected En-2 plants, such as the activation of pathogenesis-related protein gene expression and the production of camalexin, an Arabidopsis phytoalexin. Defense responses induced chemically or by mutation in the susceptible ecotypes delayed and reduced the severity of a CaMV infection. These findings suggest that CAR1 acts either in the susceptible ecotype to support virus movement or in the resistant ecotype to signal a defense response.