Pulmonary microvascular endothelial cells from bleomycin-induced rats promote the transformation and collagen synthesis of fibroblasts

Injured Endothelial Cell: A Risk Factor for Pulmonary Fibrosis

The pathological features of pulmonary fibrosis (PF) are the abnormal activation and proliferation of myofibroblasts and the extraordinary deposition of the extracellular matrix (ECM). However, the pathogenesis of PF is still indistinct. In recent years, many researchers have realized that endothelial cells had a crucial role in the development of PF. Studies have demonstrated that about 16% of the fibroblasts in the lung tissue of fibrotic mice were derived from endothelial cells. Endothelial cells transdifferentiated into mesenchymal cells via the endothelial-mesenchymal transition (E(nd)MT), leading to the excessive proliferation of endothelial-derived mesenchymal cells and the accumulation of fibroblasts and ECM. This suggested that endothelial cells, a significant component of the vascular barrier, played an essential role in PF. Herein, this review discusses E(nd)MT and its contribution to the activation of other cells in PF, which could provide new ideas for further understanding the source and activation mechanism of fibroblasts and the pathogenesis of PF.

Adiponectin ameliorates lung ischemia-reperfusion injury through SIRT1-PINK1 signaling-mediated mitophagy in type 2 diabetic rats

BACKGROUND

Diabetes mellitus (DM) is a key contributing factor to poor survival in lung transplantation recipients. Mitochondrial dysfunction is recognized as a critical mediator in the pathogenesis of diabetic lung ischemia-reperfusion (IR) injury. The protective effects of adiponectin have been demonstrated in our previous study, but the underlying mechanism remains unclear. Here we demonstrated an important role of mitophagy in the protective effect of adiponectin during diabetic lung IR injury.

METHODS

High-fat diet-fed streptozotocin-induced type 2 diabetic rats were exposed to adiponectin with or without administration of the SIRT1 inhibitor EX527 following lung transplantation. To determine the mechanisms underlying the action of adiponectin, rat pulmonary microvascular endothelial cells were transfected with SIRT1 small-interfering RNA or PINK1 small-interfering RNA and then subjected to in vitro diabetic lung IR injury.

RESULTS

Mitophagy was impaired in diabetic lungs subjected to IR injury, which was accompanied by increased oxidative stress, inflammation, apoptosis, and mitochondrial dysfunction. Adiponectin induced mitophagy and attenuated subsequent diabetic lung IR injury by improving lung functional recovery, suppressing oxidative damage, diminishing inflammation, decreasing cell apoptosis, and preserving mitochondrial function. However, either administration of 3-methyladenine (3-MA), an autophagy antagonist or knockdown of PINK1 reduced the protective action of adiponectin. Furthermore, we demonstrated that APN affected PINK1 stabilization via the SIRT1 signaling pathway, and knockdown of SIRT1 suppressed PINK1 expression and compromised the protective effect of adiponectin.

CONCLUSION

These data demonstrated that adiponectin attenuated reperfusion-induced oxidative stress, inflammation, apoptosis and mitochondrial dysfunction via activation of SIRT1- PINK1 signaling-mediated mitophagy in diabetic lung IR injury.

Secretome and Tunneling Nanotubes: A Multilevel Network for Long Range Intercellular Communication between Endothelial Cells and Distant Cells

As a cellular interface between the blood and tissues, the endothelial cell (EC) monolayer is involved in the control of key functions including vascular tone, permeability and homeostasis, leucocyte trafficking and hemostasis. EC regulatory functions require long-distance communications between ECs, circulating hematopoietic cells and other vascular cells for efficient adjusting thrombosis, angiogenesis, inflammation, infection and immunity. This intercellular crosstalk operates through the extracellular space and is orchestrated in part by the secretory pathway and the exocytosis of Weibel Palade Bodies (WPBs), secretory granules and extracellular vesicles (EVs). WPBs and secretory granules allow both immediate release and regulated exocytosis of messengers such as cytokines, chemokines, extracellular membrane proteins, coagulation or growth factors. The ectodomain shedding of transmembrane protein further provide the release of both receptor and ligands with key regulatory activities on target cells. Thin tubular membranous channels termed tunneling nanotubes (TNTs) may also connect EC with distant cells. EVs, in particular exosomes, and TNTs may contain and transfer different biomolecules (e.g., signaling mediators, proteins, lipids, and microRNAs) or pathogens and have emerged as a major triggers of horizontal intercellular transfer of information.

Characterization of the heterogeneity of endothelial cells in bleomycin-induced lung fibrosis using single-cell RNA sequencing

The loss of normal alveolar capillary and deregulated angiogenesis occurs simultaneously in idiopathic pulmonary fibrosis (IPF); however the contributions of specific endothelial subpopulations in the development of pulmonary fibrosis are poorly understood. Herein, we perform single-cell RNA sequencing to characterize the heterogeneity of endothelial cells (ECs) in bleomycin (BLM)-induced lung fibrosis in rats. One subpopulation, characterized by the expression of Nos3 and Cav1, is mostly distributed in non-fibrotic lungs and also highly expresses genes related to the “response to mechanical stimulus” and “lung/heart morphogenesis” processes. Another subpopulation of ECs expanded in BLM-treated lungs, characterized by Cxcl12, is observed to be closely related to the pro-fibrotic process in the transcriptome data, such as “regulation of angiogenesis,” “collagen binding,” and “chemokine activity,” and spatially localized to BLM-induced neovascularization. Using CellPhoneDB software, we generated a complex cell–cell interaction network, which predicts the potential roles of EC subpopulations in recruiting monocytes, inducing the proliferation of fibroblasts and promoting the production and remolding of the extracellular matrix (ECM). Taken together, our data demonstrate the high degree of heterogeneity of ECs in fibrotic lung and it is proposed that the interaction between ECs, macrophages, and stromal cells contributes to pathologic IPF.

The quiescent endothelium: signalling pathways regulating organ-specific endothelial normalcy

Endothelial cells are at the interface between circulating blood and tissues. This position confers on them a crucial role in controlling oxygen and nutrient exchange and cellular trafficking between blood and the perfused organs. The endothelium adopts a structure that is specific to the needs and function of each tissue and organ and is subject to tissue-specific signalling input. In adults, endothelial cells are quiescent, meaning that they are not proliferating. Quiescence was considered to be a state in which endothelial cells are not stimulated but are instead slumbering and awaiting activating signals. However, new evidence shows that quiescent endothelium is fully awake, that it constantly receives and initiates functionally important signalling inputs and that this state is actively regulated. Signalling pathways involved in the maintenance of functionally quiescent endothelia are starting to be identified and are a combination of endocrine, autocrine, paracrine and mechanical inputs. The paracrine pathways confer a microenvironment on the endothelial cells that is specific to the perfused organs and tissues. In this Review, we present the current knowledge of organ-specific signalling pathways involved in the maintenance of endothelial quiescence and the pathologies associated with their disruption. Linking organ-specific pathways and human vascular pathologies will pave the way towards the development of innovative preventive strategies and the identification of new therapeutic targets.

KCa3.1 channel blockade attenuates microvascular remodelling in a large animal model of bleomycin-induced pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive lung disease with limited therapeutic options and poor prognosis. IPF has been associated with aberrant vascular remodelling, however the role of vascular remodelling in pulmonary fibrosis is poorly understood. Here, we used a novel segmental challenge model of bleomycin-induced pulmonary fibrosis in sheep to evaluate the remodelling of the pulmonary vasculature, and to investigate the changes to this remodelling after the administration of the K_Ca3.1 channel inhibitor, senicapoc, compared to the FDA-approved drug pirfenidone. We demonstrate that in vehicle-treated sheep, bleomycin-infused lung segments had significantly higher blood vessel density when compared to saline-infused control segments in the same sheep. These microvascular density changes were significantly attenuated by senicapoc treatment. The increases in vascular endothelial growth factor (VEGF) expression and endothelial cell proliferation in bleomycin-infused lung segments were significantly reduced in sheep treated with the senicapoc, when compared to vehicle-treated controls. These parameters were not significantly suppressed with pirfenidone treatment. Senicapoc treatment attenuated vascular remodelling through inhibition of capillary endothelial cell proliferation and VEGF expression. These findings suggest a potential new mode of action for the novel drug senicapoc which may contribute to its efficacy in combatting pulmonary fibrosis.

Activation of PERK in ET-1- and thrombin-induced pulmonary fibroblast differentiation: Inhibitory effects of curcumin

In the present study, we investigated the role of PKR-like endoplasmic reticular kinase (PERK), an endoplasmic reticulum (ER) stress kinase, in endothelin 1 (ET-1)- and thrombin-induced pulmonary fibrosis (PF), and the preventive effects of curcumin (CUR). Using the human embryonic WI-38 lung fibroblast cell line, ET-1 and thrombin induced the expression of ER stress-related proteins (CCAAT-enhancer-binding protein homologous protein, PERK, and binding immunoglobulin protein), a profibrogenic factor (cellular communication network factor 2 [CCN2]), and differentiation markers including α-smooth muscle actin (α-SMA), collagen I (Col I), and Col IV. Knockdown of PERK expression via small interfering RNA (siRNA) significantly reduced the increases in CCN2, α-SMA, Col I, and Col IV proteins in WI-38 cells according to western blot analysis and immunohistochemistry (IHC). Activation of c-Jun N-terminal kinase (JNK) was observed in ET-1- and thrombin-treated WI-38 cells, and the addition of a JNK inhibitor (SP) suppressed the induction of the indicated proteins by ET-1 and thrombin. Thapsigargin (TG), an ER stress inducer, elevated expressions of PERK and ER stress-related proteins with increased differentiation of WI-38 cells. Knockdown of PERK by siRNA or the PERK inhibitor glycogen synthesis kinase reduced expressions of the differentiation markers, α-SMA and Col IV, in WI-38 cells. CUR concentration-dependently inhibited ET-1- or thrombin-induced CCN2, α-SMA, and vimentin proteins with decreased levels of phosphorylated mitogen-activated protein kinase and PERK in WI-38 cells. An in vivo bleomycin-induced PF study showed that an intraperitoneal injection of CUR (30 mg/kg) reduced expressions of α-SMA, CCN2, Col IV, and vimentin in lung tissues via IHC staining using specific antibodies. This study is the first to demonstrate that PERK activation contributes to pulmonary fibroblast differentiation elicited by ET-1 or thrombin, and the inhibitory activity of CUR against PF is demonstrated herein.

Endothelial Colony-Forming Cells Do Not Participate to Fibrogenesis in a Bleomycin-Induced Pulmonary Fibrosis Model in Nude Mice

Idiopathic pulmonary fibrosis (IPF) is a devastating lung disease characterized by fibroblast proliferation, extracellular matrix deposition, destruction of pulmonary alveolar architecture and vascular remodeling. Apart pirfenidone or nintendanib that only slow down the fibrotic process, there is no curative treatment other than lung transplantation. Because cell therapy approaches have been proposed in IPF, we hypothesized that injection of endothelial colony-forming cells (ECFCs), the vasculogenic subtype of endothelial progenitor cells, could modulate fibrosis in a Nude mouse model of bleomycin induced-pulmonary fibrosis. Mice were injected with ECFCs isolated from cord blood and from peripheral blood of adult IPF patients at two time-points: during the development of the fibrosis or once the fibrosis was constituted. We assessed morbidity, weight variation, collagen deposition, lung imaging by microCT, Fulton score and microvascular density. Neither ECFCs isolated from cord blood nor from IPF patients were able to modulate fibrosis or vascular density during fibrogenesis or when fibrosis was constituted. These findings indicate that human ECFCs do not promote an adaptive regenerative response in the lung upon fibrosis or angiogenic process in the setting of bleomycin-induced pulmonary fibrosis in Nude mice.

Interleukin-8 release by endothelial colony-forming cells isolated from idiopathic pulmonary fibrosis patients might contribute to their pathogenicity

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a devastating disease characterized by obliteration of alveolar architecture, resulting in declining lung function and ultimately death. Pathogenic mechanisms involve a concomitant accumulation of scar tissue together with myofibroblasts activation and a strong abnormal vascular remodeling. Endothelial progenitor cells (ECFC subtype) have been investigated in several human lung diseases as a potential actor in IPF. We previously demonstrated that ECFCs are down-regulated in IPF in contrast to healthy controls. We postulated here that ECFCs might behave as a liquid biopsy in IPF patients and that they exert modified vasculogenic properties.

METHODS AND RESULTS

ECFCs isolated from controls and IPF patients expressed markers of the endothelial lineage and did not differ concerning adhesion, migration, and differentiation in vitro and in vivo. However, senescent and apoptotic states were increased in ECFCs from IPF patients as shown by galactosidase staining, p16 expression, and annexin-V staining. Furthermore, conditioned medium of IPF-ECFCs had increased level of interleukin-8 that induced migration of neutrophils in vitro and in vivo. In addition, an infiltration by neutrophils was shown in IPF lung biopsies and we found in a prospective clinical study that a high level of neutrophils in peripheral blood of IPF patients was associated to a poor prognosis.

CONCLUSION

To conclude, our study shows that IPF patients have a senescent ECFC phenotype associated with an increased IL-8 secretion potential that might contribute to lung neutrophils invasion during IPF.

Feixian Recipe inhibits pulmonary fibrosis by targeting pulmonary microvascular endothelial cells and VEGF/VEGFR2 signaling pathway

Objective: To investigate the regulatory mechanism of PMVECs and vascular endothelial growth factor VEGF/vascular endothelial growth factor receptor 2 (VEGFR2) signaling pathway in pulmonary fibrosis and the inhibitory effect of Feixian Recipe (FXR) in pulmonary fibrosis by targeting VEGF/VEGFR2 signal pathway.

Methods: In this study, pulmonary microvascular endothelial cells (PMVECs) were successfully isolated from rats with pulmonary fibrosis. Cells were divided into six groups: model group, prednisone group, losartan group and three different concentrated (100[Formula: see text]ug/mL, 60[Formula: see text]ug/mL, 20[Formula: see text]ug/mL) FXR groups. The adhesion rate, migration and closed blood vessels of each PMVECs group were detected. The mRNA expression of VEGF, VEGFR2, phosphoinositide 3-kinase (PI3K), mitogen-activated protein kinases 38 (P38 MAPK) and activin receptor-like kinase (ALK) were detected by SYBR Green I real-time fluorescence quantitative PCR.

Results: Compared with the model group, the adhesion rate, migration and angiogenesis of PMVECs were decreased in FXR groups ([Formula: see text]). Compared with prednisone and losartan groups, the mRNA expressions of VEGF, VEGFR2, PI3K and P38 MAPK were down-regulated significantly by FXR ([Formula: see text]).

Conclution: FXR can inhibit the migration, adhesion and angiogenesis of PMVECs in rats with pulmonary fibrosis by targeting VEGF/VEGFR2 signal pathway, and inhibit the progress of pulmonary fibrosis.

Atrial natriuretic peptide protects against bleomycin-induced pulmonary fibrosis via vascular endothelial cells in mice : ANP for pulmonary fibrosis

Background

Pulmonary fibrosis is a life-threatening disease characterized by progressive dyspnea and worsening pulmonary function. Atrial natriuretic peptide (ANP), a heart-derived secretory peptide used clinically in Japan for the treatment of acute heart failure, exerts a wide range of protective effects on various organs, including the heart, blood vessels, kidneys, and lungs. Its therapeutic properties are characterized by anti-inflammatory and anti-fibrotic activities mediated by the guanylyl cyclase-A (GC-A) receptor. We hypothesized that ANP would have anti-fibrotic and anti-inflammatory effects on bleomycin (BLM)-induced pulmonary fibrosis in mice.

Methods

Mice were divided into three groups: normal control, BLM with vehicle, and BLM with ANP. ANP (0.5 μg/kg/min via osmotic-pump, subcutaneously) or vehicle administration was started before BLM administration (1 mg/kg) and continued until the mice were sacrificed. At 7 or 21 days after BLM administration, fibrotic changes and infiltration of inflammatory cells in the lungs were assessed based on histological findings and analysis of bronchoalveolar lavage fluid. In addition, fibrosis and inflammation induced by BLM were evaluated in vascular endothelium-specific GC-A overexpressed mice. Finally, attenuation of transforming growth factor-β (TGF-β) signaling by ANP was studied using immortalized mouse endothelial cells stably expressing GC-A receptor.

Results

ANP significantly decreased lung fibrotic area and infiltration of inflammatory cells in lungs after BLM administration. Furthermore, similar effects of ANP were observed in vascular endothelium–specific GC-A overexpressed mice. In cultured mouse endothelial cells, ANP reduced phosphorylation of Smad2 after TGF-β stimulation.

Conclusions

ANP exerts protective effects on BLM-induced pulmonary fibrosis via vascular endothelial cells.

The expression levels of Notch-related signaling molecules in pulmonary microvascular endothelial cells in bleomycin-induced rat pulmonary fibrosis

Previous studies have suggested that the Notch signaling pathway plays a very important role in the proliferation and differentiation of pulmonary microvascular endothelial cells (PMVECs). Therefore, we aimed to investigate the expression level of Notch-related signaling molecules in PMVECs in bleomycin (BLM)-induced rat pulmonary fibrosis. Immunohistochemistry, immunofluorescence, Western blotting, and real-time PCR were used to analyze the differences in protein and mRNA expression levels of Notch-related signaling molecules, i.e. Notch1, Jagged1, Delta-like ligand 4 (Dll4), and hairy and enhancer of split homolog 1 (Hes1), between a control group treated with intratracheal instillation of saline and a study group treated with intratracheal instillation of BLM solution. Expression levels of the receptor Notch1 and one of its ligands, Jagged1, were upregulated, while the expression levels of the ligand Dll4 and the target molecule of the Notch signaling pathway, Hes1, were downregulated. The differences in protein and mRNA expression levels between the control and study groups were significant (p<0.001). The Jagged1/Notch1 signaling pathway is activated in the pathogenesis of BLM-induced rat pulmonary fibrosis, while the Dll4/Notch1 signaling pathway is inhibited, which inhibits the suppressive effect of Dll4/Notch1 signaling on PMVEC overproliferation, further causing PMVEC dysfunction in cell sprouting and maturation as well as abnormal differentiation of the cell phenotype. Conversely, the down-expression of Hes1 indicates that the Jagged1/Notch1 signaling pathway could be a non-canonical Notch signaling pathway independent of Hes1 activation, which differs from the canonical Dll4/Notch1 signaling pathway.

Regulatory mechanisms of TGF-β1-induced fibrogenesis of human alveolar epithelial cells

Pulmonary fibrosis is characterized by an extensive activation of fibrogenic cells and deposition of extracellular matrix (ECM). Transforming growth factor (TGF)‐β1 plays a pivotal role in the pathogenesis of pulmonary fibrosis, probably through the epithelial‐ to‐mesenchymal transition (EMT) and ECM production. The present study investigates potential mechanism by which TGF‐β1 induces EMT and ECM production in the fibrogenesis of human lung epithelial cells during pulmonary fibrosis. The expression of EMT phenotype and other proteins relevant to fibrogenesis were measured and the cell bio‐behaviours were assessed using Cell‐IQ Alive Image Monitoring System. We found that TGF‐β1‐induced EMT was accompanied with increased collagen I deposition, which may be involved in the regulation of connective tissue growth factor (CTGF) and phosphoinositide 3‐kinase (PI3K) signalling pathway. Treatment with PI3K inhibitors significantly attenuated the TGF‐β1‐ induced EMT, CTGF expression and collagen I synthesis in lung epithelial cells. The interference of CTGF expression impaired the basal and TGF‐β1‐stimulated collagen I deposition, but did not affect the process of EMT. Our data indicate that the signal pathway of TGF‐β1/PI3K/CTGF plays an important role in the fibrogenesis of human lung epithelial cells, which may be a novel therapeutic approach to prevent and treat pulmonary fibrosis.

Fasudil, an inhibitor of Rho-associated coiled-coil kinase, attenuates hyperoxia-induced pulmonary fibrosis in neonatal rats

BACKGROUND

Oxygen therapy is important during the management of high-risk neonatal infants, such as those with preterm birth, low birth weight, and asphyxia. However, prolonged exposure to high oxygen concentrations can readily lead to diffuse nonspecific inflammation, which promotes airway remodeling and pulmonary fibrosis. The Rho/Rho-associated coiled-coil kinase (Rho/ROCK) signaling pathway plays an important role in numerous developmental and proliferative diseases. This study was performed to determine the efficacy of ROCK inhibitor fasudil in blocking the development of hyperoxia-induced lung injury and fibrosis in neonatal rats.

METHODS

Neonatal rats were randomly divided into four groups: air + saline group, air + fasudil group, hyperoxia + saline group, and hyperoxia + fasudil group. The hyperoxia + saline and Hyp + fasudil groups were exposed to 95% oxygen for 21 days and administered intraperitoneal saline or fasudil once daily. The air + saline and air + fasudil group were exposed to 21% oxygen (room air) and administered the same volume of intraperitoneal saline or fasudil.

RESULTS

Fasudil-treated rats exhibited improved histopathological changes and decreased lung hydroxyproline content. Fasudil attenuated the protein level of alpha-smooth muscle actin, transforming growth factor-β1, and connective tissue growth factor. Additionally, fasudil reduced the activation of ROCK1 and myosin phosphatase targeting subunit 1 protein in the Rho/ROCK signaling pathway.

CONCLUSIONS

Fasudil may be a potentially effective therapeutic drug for hyperoxia-induced pulmonary fibrosis.

Activated alveolar epithelial cells initiate fibrosis through autocrine and paracrine secretion of connective tissue growth factor

Fibrogenesis involves a pathological accumulation of activated fibroblasts and extensive matrix remodeling. Profibrotic cytokines, such as TGF-β, stimulate fibroblasts to overexpress fibrotic matrix proteins and induce further expression of profibrotic cytokines, resulting in progressive fibrosis. Connective tissue growth factor (CTGF) is a profibrotic cytokine that is indicative of fibroblast activation. Epithelial cells are abundant in the normal lung, but their contribution to fibrogenesis remains poorly defined. Profibrotic cytokines may activate epithelial cells with protein expression and functions that overlap with the functions of active fibroblasts. We found that alveolar epithelial cells undergoing TGF-β-mediated mesenchymal transition in vitro were also capable of activating lung fibroblasts through production of CTGF. Alveolar epithelial cell expression of CTGF was dramatically reduced by inhibition of Rho signaling. CTGF reporter mice demonstrated increased CTGF promoter activity by lung epithelial cells acutely after bleomycin in vivo. Furthermore, mice with lung epithelial cell-specific deletion of CTGF had an attenuated fibrotic response to bleomycin. These studies provide direct evidence that epithelial cell activation initiates a cycle of fibrogenic effector cell activation during progressive fibrosis. Therapy targeted at epithelial cell production of CTGF offers a novel pathway for abrogating this progressive cycle and limiting tissue fibrosis.

Endothelial cells recruit macrophages and contribute to a fibrotic milieu in bleomycin lung injury

Systemic sclerosis (SSc) is a systemic autoimmune disease that causes inflammation, vasculopathy, and fibrosis of the skin and internal organs. One of the most severe complications of SSc involves the development of pulmonary fibrosis. Endothelial cell injury precedes the development of fibrosis, and is believed to be an initiating event. Therefore, we aimed to characterize the role of endothelial cells in the progression of pulmonary fibrosis, using a well-established bleomycin (BLM) model of pulmonary fibrosis. Endothelial cells were isolated by cell sorting, and the analysis of gene expression was performed with quantitative RT-PCR. Endothelial injury was induced between the first and second week, as shown by the elevated expression of the vascular injury markers matrix metallopeptidase-12 and von Willebrand factor. After injury, endothelial activation was indicated by the up-regulation of selectins, CCL chemokines, and inflammatory mediators, including complement anaphylatoxin receptors (C3aR and C5aR), oncostatin M, and leukemia inhibitory factor. The endothelial cell overexpression of fibrotic mediators, including connective tissue growth factor, plasminogen activator inhibitor-1, osteopontin, fibronectin, and fibroblast specific protein-1, was observed in the second and fourth weeks. This study suggests that endothelial cells actively contribute to the disease process via multiple mechanisms, including the recruitment of inflammatory cells and the establishment of a profibrotic environment during the development of BLM-induced pulmonary fibrosis.

Proliferative phenotype of pulmonary microvascular endothelial cells plays a critical role in the overexpression of CTGF in the bleomycin-injured rat

The pathogenesis of idiopathic pulmonary fibrosis (IPF) is not very clear, with evidence for the involvement of both inflammation and aberrant vascular remodeling (associated with angiogenesis). Pulmonary microvascular endothelial cells (PMVECs), which play a major role in inflammation, secrete cytokines that promote the transformation and collagen synthesis of fibroblasts. Moreover, angiogenesis is characterized by PMVEC proliferation. The main aim of this study was to confirm the role of PMVECs in pulmonary fibrosis. Accordingly, we observed the functional changes in PMVECs in bleomycin (BLM)-treated rats (pulmonary fibrosis model) in vivo, and compared them with those of rats with pneumonia. The proliferation phenotype and intracellular ionized calcium concentration ([Ca(2+)]i) of PMVECs from BLM-treated rats were also investigated. The functioning of PMVECs was abnormal in BLM-injured rats, particularly with regard to their proliferation and secretion of connective tissue growth factor (CTGF). [Ca(2+)]i was increased in the proliferated PMVECs from BLM-treated rats. The findings suggest that dysfunction of PMVECs characterized by overexpression of CTGF is critical in rat pulmonary injury induced by BLM, and is probably related with the proliferative phenotype and [Ca(2+)]i overload. It can be concluded from the results that proliferation of PMVECs plays an important role in the pathogenesis of BLM-induced PF.

Activated alveolar epithelial cells initiate fibrosis through secretion of mesenchymal proteins

Fibrosis is characterized by accumulation of activated fibroblasts and pathological deposition of fibrillar collagens. Activated fibroblasts overexpress matrix proteins and release factors that promote further recruitment of activated fibroblasts, leading to progressive fibrosis. The contribution of epithelial cells to this process remains unknown. Epithelium-directed injury may lead to activation of epithelial cells with phenotypes and functions similar to activated fibroblasts. Prior reports that used a reporter gene fate-mapping strategy are limited in their ability to investigate the functional significance of epithelial cell-derived mesenchymal proteins during fibrogenesis. We found that lung epithelial cell-derived collagen I activates fibroblast collagen receptor discoidin domain receptor-2, contributes significantly to fibrogenesis, and promotes resolution of lung inflammation. Alveolar epithelial cells undergoing transforming growth factor-β-mediated mesenchymal transition express several other secreted profibrotic factors and are capable of activating lung fibroblasts. These studies provide direct evidence that activated epithelial cells produce mesenchymal proteins that initiate a cycle of fibrogenic effector cell activation, leading to progressive fibrosis. Therapy targeted at epithelial cell production of type I collagen offers a novel pathway for abrogating this progressive cycle and for limiting tissue fibrosis but may lead to sustained lung injury/inflammation.

Interferon-γ promotes vascular remodeling in human microvascular endothelial cells by upregulating endothelin (ET)-1 and transforming growth factor (TGF) β2

Systemic sclerosis (SSc) is a complex disease characterized by vascular alterations, activation of the immune system and tissue fibrosis. Previous studies have implicated activation of the interferon pathways in the pathogenesis of SSc. The goal of this study was to determine whether interferon type I and/or type II could play a pathogenic role in SSc vasculopathy. Human dermal microvascular endothelial cells (HDMVECs) and fibroblasts were obtained from foreskins of healthy newborns. The RT Profiler PCR Array System was utilized to screen for EndoMT genes. Treatment with IFN-α or IFN-γ downregulated Fli1 and VE-cadherin. In contrast, IFN-α and IFN-γ exerted opposite effects on the expression of α-SMA, CTGF, ET-1, and TGFβ2, with IFN-α downregulating and IFN-γ upregulating this set of genes. Blockade of TGFβ signaling normalized IFN-γ-mediated changes in Fli1, VE-cadherin, CTGF, and ET-1 levels, whereas upregulation of α-SMA and TGFβ2 was not affected. Bosentan treatment was more effective than TGFβ blockade in reversing the actions of IFN-γ, including downregulation of α-SMA and TGFβ2, suggesting that activation of the ET-1 pathway plays a main role in the IFN-γ responses in HDMECs. IFN-γ induced expression of selected genes related to endothelial-to-mesenchymal transition (EndoMT), including Snail1, FN1, PAI1, TWIST1, STAT3, RGS2, and components of the WNT pathway. The effect of IFN-γ on EndoMT was mediated via TGFβ2 and ET-1 signaling pathways. This study demonstrates distinct effects of IFN-α and IFN-γ on the biology of vascular endothelial cells. IFN-γ may contribute to abnormal vascular remodeling and fibrogenesis in SSc, partially via induction of EndoMT.

Imbalance of circulating endothelial cells and progenitors in idiopathic pulmonary fibrosis

BACKGROUND

Fibrogenesis during idiopathic pulmonary fibrosis (IPF) is strongly associated with abnormal vascular remodeling. Respective abundance of circulating endothelial cells (CEC) and endothelial progenitor cells (EPC) might reflect the balance between vascular injury and repair and potentially serve as biomarkers of the disease.

OBJECTIVES AND METHODS

We postulated that CEC and EPC subtypes might be differently modulated in IPF. Sixty-four consecutive patients with newly diagnosed IPF were prospectively enrolled and compared to thirteen healthy volunteers. CEC were counted with immunomagnetic CD146-coated beads; progenitors CD34+45(dim)/CD34+133+/CD34+KDR+were assessed through flow cytometry and EPC (colony-forming-units-Endothelial Cells, CFU-EC, and endothelial colonies forming cells, ECFC) were quantified by cell culture assays.

RESULTS

IPF patients were characterized by a marked increase in CEC associated to an EPC defect: both CD34(+)KDR(+) cells and CFU-EC were decreased versus controls. Moreover, in IPF subjects with a low diffusing capacity of the lung for carbon monoxide (DL(CO)) < 40 %, CFU-EC and ECFC were higher compared to those with DL(CO) > 40 %. Finally, ECFC were negatively correlated with DL(CO). During an 18 month follow up, CEC levels increased in patients with exacerbation, including those who died during follow up. Finally, ECFC from patients with exacerbation proliferative potential was strongly increased.

CONCLUSION

IPF is basically associated with both a vascular injury and a repair defect. This study highlights an adaptative process of EPC mobilization in the most severe forms of IPF, that could reflect enhanced homing to the pulmonary vasculature, which clinical consequences remain to be determined.