[64Cu]Cu-PEG-FUD peptide for noninvasive and sensitive detection of murine pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease resulting in irreversible scarring within the lungs. However, the lack of biomarkers that enable real-time assessment of disease activity remains a challenge in providing efficient clinical decision-making and optimal patient care in IPF. Fibronectin (FN) is highly expressed in fibroblastic foci of the IPF lung where active extracellular matrix (ECM) deposition occurs. Functional upstream domain (FUD) tightly binds the N-terminal 70-kilodalton domain of FN that is crucial for FN assembly. In this study, we first demonstrate the capacity of PEGylated FUD (PEG-FUD) to target FN deposition in human IPF tissue ex vivo. We subsequently radiolabeled PEG-FUD with 64Cu and monitored its spatiotemporal biodistribution via µPET/CT imaging in mice using the bleomycin-induced model of pulmonary injury and fibrosis. We demonstrated [64Cu]Cu-PEG-FUD uptake 3 and 11 days following bleomycin treatment, suggesting that radiolabeled PEG-FUD holds promise as an imaging probe in aiding the assessment of fibrotic lung disease activity.

An open microfluidic coculture model of fibroblasts and eosinophils to investigate mechanisms of airway inflammation.

Interactions between fibroblasts and immune cells play an important role in tissue inflammation. Previous studies have found that eosinophils activated with interleukin-3 (IL-3) degranulate on aggregated immunoglobulin G (IgG) and release mediators that activate fibroblasts in the lung. However, these studies were done with eosinophil-conditioned media that have the capacity to investigate only one-way signaling from eosinophils to fibroblasts. Here, we demonstrate a coculture model of primary normal human lung fibroblasts (HLFs) and human blood eosinophils from patients with allergy and asthma using an open microfluidic coculture device. In our device, the two types of cells can communicate via two-way soluble factor signaling in the shared media while being physically separated by a half wall. Initially, we assessed the level of eosinophil degranulation by their release of eosinophil-derived neurotoxin (EDN). Next, we analyzed the inflammation-associated genes and soluble factors using reverse transcription quantitative polymerase chain reaction (RT-qPCR) and multiplex immunoassays, respectively. Our results suggest an induction of a proinflammatory fibroblast phenotype of HLFs following the coculture with degranulating eosinophils, validating our previous findings. Additionally, we present a new result that indicate potential impacts of activated HLFs back on eosinophils. This open microfluidic coculture platform provides unique opportunities to investigate the intercellular signaling between the two cell types and their roles in airway inflammation and remodeling.

Selective Inhibition of Bromodomain-Containing Protein 4 Reduces Myofibroblast Transdifferentiation and Pulmonary Fibrosis.

Idiopathic pulmonary fibrosis is a lethal disease driven by myofibroblast expansion. Currently no therapies exist that target the epigenetic mechanisms controlling myofibroblast transdifferentiation, which is responsible for unregulated extracellular matrix (ECM) production. We have recently shown that bromodomain-containing protein 4 (BRD4), an epigenetic regulator that forms a scaffold for nuclear activators and transcription factors, is essential for TGFß-induced myofibroblast transdifferentiation. However, its role in the development and progression of pulmonary fibrosis in vivo has not been established. Here, we evaluate the hypothesis that BRD4 bromodomain interactions mediate myofibroblast expansion and fibrosing disease in vivo. C57BL/6J mice challenged with intratracheal bleomycin were systemically treated with a selective allosteric inhibitor of the BRD4 bromodomain 1 (BD1), ZL0591 (10 mg/kg), during the established fibrotic phase (14 days post-bleomycin) in a rigorous therapeutic paradigm. Eleven days after initiation of ZL0591 treatment (25 days post-bleomycin), we detected a significant improvement in blood O2 saturation compared to bleomycin/vehicle control. Twenty-eight days post-bleomycin, we observed a reduction in the volumetric Hounsfield Unit (HU) density by micro computed tomography (µCT) in the ZL0591-treated group, as well as a reduction in collagen deposition (hydroxyproline content) and severity of injury (Ashcroft scoring). Myofibroblast transdifferentiation was measured by smooth muscle α-actin (αSMA) staining, indicating a loss of this cell population in the ZL0591-treated group, and corresponded to reduced transcript levels of myofibroblast-associated extracellular matrix genes, tenascin-C and collagen 1α1. We conclude that BRD4 BD1 interactions are critical for myofibroblast transdifferentiation and fibrotic progression in a mouse model of pulmonary fibrosis.

Autophagy Protects against Eosinophil Cytolysis and Release of DNA.

The presence of eosinophils in the airway is associated with asthma severity and risk of exacerbations. Eosinophils deposit their damaging products in airway tissue, likely by degranulation and cytolysis. We previously showed that priming blood eosinophils with IL3 strongly increased their cytolysis on aggregated IgG. Conversely, IL5 priming did not result in significant eosinophil cytolysis in the same condition. Therefore, to identify critical events protecting eosinophils from cell cytolysis, we examined the differential intracellular events between IL5- and IL3-primed eosinophils interacting with IgG. We showed that both IL3 and IL5 priming increased the eosinophil adhesion to IgG, phosphorylation of p38, and production of reactive oxygen species (ROS), and decreased the phosphorylation of cofilin. However, autophagic flux as measured by the quantification of SQSTM1-p62 and lipidated-MAP1L3CB over time on IgG, with or without bafilomycin-A1, was higher in IL5-primed compared to IL3-primed eosinophils. In addition, treatment with bafilomycin-A1, an inhibitor of granule acidification and autophagolysosome formation, enhanced eosinophil cytolysis and DNA trap formation in IL5-primed eosinophils. Therefore, this study suggests that increased autophagy in eosinophils protects from cytolysis and the release of DNA, and thus limits the discharge of damaging intracellular eosinophilic contents.

[68 Ga]Ga-FAPI-46 PET for non-invasive detection of pulmonary fibrosis disease activity.

PURPOSE: The lack of effective molecular biomarkers to monitor idiopathic pulmonary fibrosis (IPF) activity or treatment response remains an unmet clinical need. Herein, we determined the utility of fibroblast activation protein inhibitor for positron emission tomography (FAPI PET) imaging in a mouse model of pulmonary fibrosis. METHODS: Pulmonary fibrosis was induced by intratracheal administration of bleomycin (1 U/kg) while intratracheal saline was administered to control mice. Subgroups from each cohort (n = 3-5) underwent dynamic 1 h PET/CT after intravenously injecting FAPI-46 radiolabeled with gallium-68 ([68 Ga]Ga-FAPI-46) at 7 days and 14 days following disease induction. Animals were sacrificed following imaging for ex vivo gamma counting and histologic correlation. [68 Ga]Ga-FAPI-46 uptake was quantified and reported as percent injected activity per cc (%IA/cc) or percent injected activity (%IA). Lung CT density in Hounsfield units (HU) was also correlated with histologic examinations of lung fibrosis. RESULTS: CT only detected differences in the fibrotic response at 14 days post-bleomycin administration. [68 Ga]Ga-FAPI-46 lung uptake was significantly higher in the bleomycin group than in control subjects at 7 days and 14 days. Significantly (P = 0.0012) increased [68 Ga]Ga-FAPI-46 lung uptake in the bleomycin groups at 14 days (1.01 ± 0.12%IA/cc) vs. 7 days (0.33 ± 0.09%IA/cc) at 60 min post-injection of the tracer was observed. These findings were consistent with an increase in both fibrinogenesis and FAP expression as seen in histology. CONCLUSION: CT was unable to assess disease activity in a murine model of IPF. Conversely, FAPI PET detected both the presence and activity of lung fibrogenesis, making it a promising tool for assessing early disease activity and evaluating the efficacy of therapeutic interventions in lung fibrosis patients.

Expression of serum response factor in the lung mesenchyme is essential for development of pulmonary fibrosis.

Extracellular matrix deposition characterizes idiopathic pulmonary fibrosis (IPF) and is orchestrated by myofibroblasts. The lung mesenchyme is an essential source of myofibroblasts in pulmonary fibrosis. Although the transcription factor serum response factor (SRF) has shown to be critical in the process of myofibroblast differentiation, its role in development of pulmonary fibrosis has not been determined in vivo. In this study, we observed that SRF expression localized to mesenchymal compartments, areas of dense fibrosis, and fibroblastic foci in human (IPF and normal) and bleomycin-treated mouse lungs. To determine the role of mesenchymal SRF in pulmonary fibrosis, we utilized a doxycycline-inducible, Tbx4 lung enhancer (Tbx4LE)-driven Cre-recombinase to disrupt SRF expression in the lung mesenchyme in vivo. Doxycycline-treated Tbx4LE-rtTA/TetO-Cre/tdTom/SRFf,f (and controls) were treated with a single intratracheal dose of bleomycin to induce pulmonary fibrosis and examined for lung mesenchymal expansion, pulmonary fibrosis, and inflammatory response. Bleomycin-treated Tbx4LE-rtTA/TetO-Cre/tdTom/SRFf,f mice showed decreased numbers of Tbx4LE-positive lung mesenchymal cells (LMCs) and collagen accumulation (via hydroxyproline assay) compared with controls. This effect was associated with SRF-null LMCs losing their proliferative and myofibroblast differentiation potential compared with SRF-positive controls. Together, these data demonstrate that SRF plays a critical role in LMC myofibroblast expansion during bleomycin-induced pulmonary fibrosis. This sets the stage for pharmacological strategies that specifically target SRF in the lung mesenchyme as a potential means of treating pulmonary fibrosis.

Interleukin-1α Is a Critical Mediator of the Response of Human Bronchial Fibroblasts to Eosinophilic Inflammation.

Eosinophils contribute to allergic inflammation in asthma in part via elaboration of a complex milieu of soluble mediators. Human bronchial fibroblasts (HBF) respond to stimulation by these mediators by acquiring a pro-inflammatory profile including induction of interleukin 6 (IL6) and IL8. This study sought to determine key component(s) of eosinophil soluble factors that mediate IL6 and IL8 induction in HBF. HBF treated with eosinophil-derived soluble mediators were analyzed for gene expression, intracellular signaling, and IL6 and IL8 secretion following inhibition of inflammatory signaling. Segmental allergen bronchoprovocation (SBP-Ag) was performed in mild asthmatics and bronchoalveolar lavage fluid was analyzed for eosinophils and cytokines. We found that signaling via the IL1α/IL1 receptor is an essential component of the response of HBF to eosinophil-derived soluble factors. IL1α-dependent activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) signaling is required to induce IL6 secretion. However, NFκB signaling is dispensable for the induction of IL8, whereas Src is required. IL1α is associated with eosinophilic inflammation in human airways after SBP-Ag. Conclusions: IL1α appears to be a critical component of the soluble eosinophil-derived milieu that drives pro-inflammatory bronchial fibroblast responses and associates with eosinophilic inflammation following SBP-Ag. Disruption of IL1α-signaling could modify the downstream effects of eosinophilic inflammation on airway remodeling.

Analysis of fibroblast migration dynamics in idiopathic pulmonary fibrosis using image-based scaffolds of the lung extracellular matrix.

Idiopathic pulmonary fibrosis (IPF) is characterized by a profound remodeling of the collagen in the extracellular matrix (ECM), where the fibers become both denser and more highly aligned. However, it is unknown how this reconfiguration of the collagen matrix affects disease progression. Here, we investigate the role of specific alterations in collagen fiber organization on cell migration dynamics by using biomimetic image-based collagen scaffolds representing normal and fibrotic lung, where the designs are derived directly from high-resolution second harmonic generation microscopy images. The scaffolds are fabricated by multiphoton-excited (MPE) polymerization, where the process is akin to three-dimensional printing, except that it is performed at much greater resolution (∼0.5 microns) and with collagen and collagen analogs. These scaffolds were seeded with early passaged primary human normal and IPF fibroblasts to enable the decoupling of the effect of cell-intrinsic characteristics (normal vs. IPF) versus ECM structure (normal vs. IPF) on migration dynamics. We found that the highly aligned IPF collagen structure promoted enhanced cell elongation and F-actin alignment along with increased cell migration speed and straightness relative to the normal tissues. Collectively, the data are consistent with an enhanced contact guidance mechanism on the aligned IPF matrix. Although cell intrinsic effects were observed, the aligned collagen matrix morphology had a larger effect on these metrics. Importantly, these biomimetic models of the lung cannot be synthesized by conventional fabrication methods. We suggest that the MPE image-based fabrication method will enable additional hypothesis-based testing studies of cell-matrix interactions in the context of tissue fibrosis.

Eosinophil cytolysis on Immunoglobulin G is associated with microtubule formation and suppression of rho-associated protein kinase signalling.

BACKGROUND: The presence of eosinophils in the airway is associated with asthma severity and risk of exacerbations. Cell-free eosinophil granules are found in tissues in eosinophilic diseases, including asthma. This suggests that eosinophils have lysed and released cellular content, likely harming tissues. OBJECTIVE: The present study explores the mechanism of CD32- and αMß2 integrin-dependent eosinophil cytolysis of IL3-primed blood eosinophils seeded on heat-aggregated immunoglobulin G (HA-IgG). METHODS: Cytoskeletal events and signalling pathways potentially involved in cytolysis were assessed using inhibitors. The level of activation of the identified events and pathways involved in cytolysis was measured. In addition, the links between these identified pathways and changes in degranulation (exocytosis) and adhesion were analysed. RESULTS: Cytolysis of IL3-primed eosinophils was dependent on the production of reactive oxygen species (ROS) and downstream phosphorylation of p-38 MAPK. In addition, formation of microtubule (MT) arrays was necessary for cytolysis and was accompanied by changes in MT dynamics as measured by phosphorylation status of stathmin and microtubule-associated protein 4 (MAP4), the latter of which was regulated by ROS production. Reduced ROCK signalling preceded cytolysis, which was associated with eosinophil adhesion and reduced migration. CONCLUSION AND CLINICAL RELEVANCE: In this CD32- and αMß2 integrin-dependent adhesion model, lysing eosinophils exhibit reduced migration and ROCK signalling, as well as both MT dynamic changes and p-38 phosphorylation downstream of ROS production. We propose that interfering with these pathways would modulate eosinophil cytolysis and subsequent eosinophil-driven tissue damage.

Pdgfra marks a cellular lineage with distinct contributions to myofibroblasts in lung maturation and injury response.

Pdgfra-expressing (Pdgfra+) cells have been implicated as progenitors in many mesenchymal tissues. To determine lineage potential, we generated PdgfrartTA knockin mice using CRISPR/Cas9. During lung maturation, counter to a prior study reporting that Pdgfra+ cells give rise equally to myofibroblasts and lipofibroblasts, lineage tracing using PdgfrartTA;tetO-cre mice indicated that ~95% of the lineaged cells are myofibroblasts. Genetic ablation of Pdgfra+ cells using PdgfrartTA-driven diphtheria toxin (DTA) led to alveolar simplification, demonstrating that these cells are essential for building the gas exchange surface area. In the adult bleomycin model of lung fibrosis, lineaged cells increased to contribute to pathological myofibroblasts. In contrast, in a neonatal hyperoxia model of bronchopulmonary dysplasia (BPD), lineaged cells decreased and do not substantially contribute to pathological myofibroblasts. Our findings revealed complexity in the behavior of the Pdgfra-lineaged cells as exemplified by their distinct contributions to myofibroblasts in normal maturation, BPD and adult fibrosis.

RNA-sequencing analysis of lung primary fibroblast response to eosinophil-degranulation products predicts downstream effects on inflammation, tissue remodeling and lipid metabolism.

BACKGROUND: The association of eosinophils with inflammation and tissue remodeling is at least partially due to their release of toxic granule proteins and other mediators, including cytokines. Tissue remodeling and consequent functional defects are affected by activity of connective tissue fibroblasts. Exaggerated fibroblast activation, accumulation and change of phenotype may lead to fibrosis and loss of tissue function. So far, little information has been reported on how eosinophils affect inflammation and tissue remodeling via the activation of fibroblasts. We have recently shown that eosinophil activation with IL-3 led to a robust eosinophil degranulation on immunoglobin-G (IgG) coated plates. Thus, in the present study, we analyze the effects of IL-3-activated eosinophil degranulation products on primary human lung fibroblasts (HLF) using whole transcriptome sequencing. METHODS: Conditioned media was obtained from eosinophils that were pre-activated with IL-3 or IL-5 and subsequently cultured for 6 h on IgG to induce degranulation. This conditioned media was added on human lung fibroblasts (HLF) for 24 h and the cell lysates were then subjected to whole transcriptome sequencing to identify global changes in gene expression. Differentially expressed genes were analyzed using the Ingenuity Pathway Analysis (IPA), and validated by qPCR. RESULTS: In HLF, the expression level of 300 genes was changed by conditioned media from IL-3-activated eosinophils compared to control fibroblast cultures. Among these 300 genes, the expression level of 35 genes coding for known proteins was upregulated by IL-3- versus IL-5-pre-activated eosinophils. Of the 35 upregulated genes, IPA identified C3, CH25H, CXCL1, CXCL8, CYP1A1, ICAM1, IL6 and UCN2 as having downstream functions on inflammation, tissue remodeling and lipid synthesis. This analysis combined with previous RNA sequencing analyses of eosinophils suggest IL-1ß, OSM and TNFSF12 as potential upstream regulators of fibroblasts. CONCLUSIONS: This study has identified several novel pro-inflammatory and pro-remodeling mediators produced by fibroblasts in response to activated eosinophils. These findings may have significant implications on the role of eosinophil/fibroblast interactions in eosinophilic disorders.

Endogenous Semaphorin-7A Impedes Human Lung Fibroblast Differentiation.

Semaphorin-7A is a glycosylphosphatidylinositol-anchored protein, initially characterized as an axon guidance protein. Semaphorin-7A also contributes to immune cell regulation and may be an essential pro-fibrotic factor when expressed by non-fibroblast cell types (exogenous). In mouse models, semaphorin-7A was shown to be important for TGF-ß1-induced pulmonary fibrosis characterized by myofibroblast accumulation and extracellular matrix deposition, but the cell-specific role of semaphorin-7A was not examined in fibroblasts. The purpose of this study is to determine semaphorin-7A expression by fibroblasts and to investigate the function of endogenously expressed semaphorin-7A in primary human lung fibroblasts (HLF). Herein, we show that non-fibrotic HLF expressed high levels of cell surface semaphorin-7A with little dependence on the percentage of serum or recombinant TGF-ß1. Semaphorin-7A siRNA strongly decreased semaphorin-7A mRNA expression and reduced cell surface semaphorin-7A. Reduction of semaphorin-7A induced increased proliferation and migration of non-fibrotic HLF. Also, independent of the presence of TGF-ß1, the decline of semaphorin-7A by siRNA was associated with increased α-smooth muscle actin production and gene expression of periostin, fibronectin, laminin, and serum response factor (SRF), indicating differentiation into a myofibroblast. Conversely, overexpression of semaphorin-7A in the NIH3T3 fibroblast cell line reduced the production of pro-fibrotic markers. The inverse association between semaphorin-7A and pro-fibrotic fibroblast markers was further analyzed using HLF from idiopathic pulmonary fibrosis (IPF) (n = 6) and non-fibrotic (n = 7) lungs. Using these 13 fibroblast lines, we observed that semaphorin-7A and periostin expression were inversely correlated. In conclusion, our study indicates that endogenous semaphorin-7A in HLF plays a role in maintaining fibroblast homeostasis by preventing up-regulation of pro-fibrotic genes. Therefore, endogenous and exogenous semaphorin-7A may have opposite effects on the fibroblast phenotype.

The Novel mTOR Complex 1/2 Inhibitor P529 Inhibits Human Lung Myofibroblast Differentiation.

Idiopathic pulmonary fibrosis is a progressive and deadly disorder with very few therapeutic options. Palomid 529 (8-(1-hydroxyethyl)-2-methoxy-3-(4-methoxybenzyloxy)-benzo[c]chromen-6-one; P529) is a novel dual inhibitor of mechanistic target of rapamycin complex 1/2 (mTORC1/2). In these studies, we investigated the effect of P529 on TGF-ß-dependent signaling and myofibroblast differentiation. TGF-ß-induced phosphorylation of the mTORC1 targets, p70 S6 kinase 1 (S6K1), and eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1), were both dose dependently inhibited by P529 in human lung fibroblasts with maximal inhibition occurring between 10 and 20 µM. mTORC2-mediated phosphorylation of Akt at the S473 site was partially inhibited with a similar dose dependency, as was TGF-ß-induced myofibroblast differentiation. Protein levels of TGF-ß-induced fibronectin and collagen were similarly decreased by P529. At this dose, there was also inhibition of mRNA transcript levels for Col1 and α-SMA, suggesting inhibition of transcriptional activation. However, there was no effect of P529 on canonical TGF-ß-induced Smad signaling, as assessed by receptor-associated Smad2/3 phosphorylation, Smad2/3/4 translocation, or Smad-driven gene expression, as assessed by Smad-binding element driven luciferase. Conversely, activation of mTORC1/2 signaling was dependent on TGF-ß type I receptor (ALK5) signaling and on Smad2/3 expression. P529 treatment disrupted TGF-ß-induced actin stress fiber formation during myofibroblast differentiation, the deposition of new extracellular fibronectin matrix, and linear wound closure by fibroblasts. Likewise, mTOR knockdown inhibited TGF-ß-induced myofibroblast differentiation. In conclusion, P529 inhibits TGF-ß-induced myofibroblast differentiation, actin stress fiber formation, and matrix protein expression and deposition. Inhibition of mTORC1/2 by P529 may be a promising approach to inhibit in vivo fibrosis. J. Cell. Biochem. 118: 2241-2249, 2017. © 2017 Wiley Periodicals, Inc.

Tensin 1 Is Essential for Myofibroblast Differentiation and Extracellular Matrix Formation.

Myofibroblasts, the primary effector cells that mediate matrix remodeling during pulmonary fibrosis, rapidly assemble an extracellular fibronectin matrix. Tensin (TNS) 1 is a key component of specialized cellular adhesions (fibrillar adhesions) that bind to extracellular fibronectin fibrils. We hypothesized that TNS1 may play a role in modulating myofibroblast-mediated matrix formation. We found that TNS1 expression is increased in fibroblastic foci from lungs with idiopathic pulmonary fibrosis. Transforming growth factor (TGF)-ß profoundly up-regulates TNS1 expression with kinetics that parallel the expression of the myofibroblast marker, smooth muscle α-actin. TGF-ß-induced TNS1 expression is dependent on signaling through the TGF-ß receptor 1 and is Rho coiled-coiled kinase/actin/megakaryoblastic leukemia-1/serum response factor dependent. Small interfering RNA-mediated knockdown of TNS1 disrupted TGF-ß-induced myofibroblast differentiation, without affecting TGF-ß/Smad signaling. In contrast, loss of TNS1 resulted in disruption of focal adhesion kinase phosphorylation, focal adhesion formation, and actin stress fiber development. Finally, TNS1 was essential for the formation of fibrillar adhesions and the assembly of nascent fibronectin and collagen matrix in myofibroblasts. In summary, our data show that TNS1 is a novel megakaryoblastic leukemia-1-dependent gene that is induced during pulmonary fibrosis. TNS1 plays an essential role in TGF-ß-induced myofibroblast differentiation and myofibroblast-mediated formation of extracellular fibronectin and collagen matrix. Targeted disruption of TNS1 and associated signaling may provide an avenue to inhibit tissue fibrosis.

In Vivo Tracking of Human Neural Progenitor Cells in the Rat Brain Using Magnetic Resonance Imaging Is Not Enhanced by Ferritin Expression.

Rapid growth in the field of stem cell research has generated a lot of interest in their therapeutic use, especially in the treatment of neurodegenerative diseases. Specifically, human neural progenitor cells (hNPCs), unique in their capability to differentiate into cells of the neural lineage, have been widely investigated due to their ability to survive, thrive, and migrate toward injured tissues. Still, one of the major roadblocks for clinical applicability arises from the inability to monitor these cells following transplantation. Molecular imaging techniques, such as magnetic resonance imaging (MRI), have been explored to assess hNPC transplant location, migration, and survival. Here we investigated whether inducing hNPCs to overexpress ferritin (hNPCs(Fer)), an iron storage protein, is sufficient to track these cells long term in the rat striatum using MRI. We found that increased hypointensity on MRI images could establish hNPC(Fer) location. Unexpectedly, however, wild-type hNPC transplants were detected in a similar manner, which is likely due to increased iron accumulation following transplantation-induced damage. Hence, we labeled hNPCs with superparamagnetic iron oxide (SPIO) nanoparticles to further increase iron content in an attempt to enhance cell contrast in MRI. SPIO-labeling of hNPCs (hNPCs-SPIO) achieved increased hypointensity, with significantly greater area of decreased T2* compared to hNPC(Fer) (p < 0.0001) and all other controls used. However, none of the techniques could be used to determine graft rejection in vivo, which is imperative for understanding cell behavior following transplantation. We conclude that in order for cell survival to be monitored in preclinical and clinical settings, another molecular imaging technique must be employed, including perhaps multimodal imaging, which would utilize MRI along with another imaging modality.

Megakaryoblastic leukemia-1 is required for the development of bleomycin-induced pulmonary fibrosis.

BACKGROUND: Fibrosing disorders of the lung, such as idiopathic pulmonary fibrosis, are characterized by progressive extracellular matrix accumulation that is driven by myofibroblasts. The transcription factor megakaryoblastic leukemia-1 (MKL1) mediates myofibroblast differentiation in response to several profibrotic stimuli, but the role it plays in mediating pulmonary fibrosis has not been fully elucidated. In this study, we utilized mice that had a germline deletion of MKL1 (MKL1 (-,-)) to determine the role that MKL1 plays in the development of bleomycin-induced pulmonary fibrosis. METHODS: Bleomycin or normal saline were intratracheally delivered to 9 to 12 week old female MKL1 (+,+) and MKL1 (-,-) mice. Mice were assessed for weight loss and survival to 28 days. Inflammatory responses were assessed through bronchoalveolar lavage at days 3 and 7 post-treatment. The development of pulmonary fibrosis was characterized using hydroxyproline assay and histological staining. MKL1 (+,+) and MKL1 (-,-) mouse lung fibroblasts were isolated to compare morphologic, gene expression and functional differences. RESULTS: MKL1 (-,-) mice demonstrated increased survival, attenuated weight loss, and decreased collagen accumulation compared to wild-type animals 28-days after intratracheal instillation of bleomycin. Histological analysis demonstrated decreased trichrome, smooth muscle α-actin, and fibronectin staining in MKL1(-,-) mice compared to MKL1 (+,+) controls. Differential cell counts from bronchoalveolar lavage demonstrated that there was attenuated neutrophilia 3 days after bleomycin administration, but no difference at day 7. Isolated mouse lung fibroblasts from MKL1 (-,-) mice had decreased contractility and deposited less fibronectin matrix compared to wild-type controls, suggesting a defect in key remodeling functions. CONCLUSIONS: Altogether, these data demonstrate that MKL1 plays a significant role in mediating the fibrotic response to bleomycin injury. Loss of MKL1 attenuated early neutrophil influx, as well as myofibroblast-mediated remodeling. Targeting MKL1 activity may therefore be a useful strategy in treating pulmonary fibrosis.

Myofibroblasts exhibit enhanced fibronectin assembly that is intrinsic to their contractile phenotype.

Myofibroblasts have increased expression of contractile proteins and display augmented contractility. It is not known if the augmented contractile gene expression characterizing the myofibroblast phenotype impacts its intrinsic ability to assemble fibronectin (FN) and extracellular matrix. In this study we investigated whether myofibroblasts displayed increased rates of FN fibril assembly when compared with their undifferentiated counterparts. Freshly plated myofibroblasts assemble exogenous FN (488-FN) into a fibrillar matrix more rapidly than fibroblasts that have not undergone myofibroblast differentiation. The augmented rate of FN matrix formation by myofibroblasts was dependent on intact Rho/Rho kinase (ROCK) and myosin signals inasmuch as treatment with Y27632 or blebbistatin attenuated 488-FN assembly. Inhibiting contractile gene expression by pharmacologic disruption of the transcription factors megakaryoblastic leukemia-1 (MKL1)/serum response factor (SRF) during myofibroblast differentiation resulted in decreased contractile force generation and attenuated 488-FN incorporation although not FN expression. Furthermore, disruption of the MKL1/SRF target gene, smooth muscle α-actin (α-SMA) via siRNA knockdown resulted in attenuation of 488-FN assembly. In conclusion, this study demonstrates a linkage between increased contractile gene expression, most importantly α-SMA, and the intrinsic capacity of myofibroblasts to assemble exogenous FN into fibrillar extracellular matrix.

In vivo tracking of human neural progenitor cells in the rat brain using bioluminescence imaging.

BACKGROUND: Stem cell therapies appear promising for treating certain neurodegenerative disorders and molecular imaging methods that track these cells in vivo could answer some key questions regarding their survival and migration. Bioluminescence imaging (BLI), which relies on luciferase expression in these cells, has been used for this purpose due to its high sensitivity. NEW METHOD: In this study, we employ BLI to track luciferase-expressing human neural progenitor cells (hNPC(Luc2)) in the rat striatum long-term. RESULTS: We show that hNPC(Luc2) are detectable in the rat striatum. Furthermore, we demonstrate that using this tracking method, surviving grafts can be detected in vivo for up to 12 weeks, while those that were rejected do not produce bioluminescence signal. We also demonstrate the ability to discern hNPC(Luc2) contralateral migration. COMPARISON WITH EXISTING METHODS: Some of the advantages of BLI compared to other imaging methods used to track progenitor/stem cells include its sensitivity and specificity, low background signal and ability to distinguish surviving grafts from rejected ones over the long term while the blood-brain barrier remains intact. CONCLUSIONS: These new findings may be useful in future preclinical applications developing cell-based treatments for neurodegenerative disorders.

Neonatal immune-tolerance in mice does not prevent xenograft rejection.

Assessing the efficacy of human stem cell transplantation in rodent models is complicated by the significant immune rejection that occurs. Two recent reports have shown conflicting results using neonatal tolerance to xenografts in rats. Here we extend this approach to mice and assess whether neonatal tolerance can prevent the rapid rejection of xenografts. In three strains of neonatal immune-intact mice, using two different brain transplant regimes and three independent stem cell types, we conclusively show that there is rapid rejection of the implanted cells. We also address specific challenges associated with the generation of humanized mouse models of disease.