Fibroblast growth factor receptor 1 is a key inhibitor of TGFβ signaling in the endothelium

Elucidating the crosstalk between endothelial-to-mesenchymal transition (EndoMT) and endothelial autophagy in the pathogenesis of atherosclerosis

Atherosclerosis, a chronic systemic inflammatory condition, is implicated in most cardiovascular ischemic events. The pathophysiology of atherosclerosis involves various cell types and associated processes, including endothelial cell activation, monocyte recruitment, smooth muscle cell migration, involvement of macrophages and foam cells, and instability of the extracellular matrix. The process of endothelial-to-mesenchymal transition (EndoMT) has recently emerged as a pivotal process in mediating vascular inflammation associated with atherosclerosis. This transition occurs gradually, with a significant portion of endothelial cells adopting an intermediate state, characterized by a partial loss of endothelial-specific gene expression and the acquisition of "mesenchymal" traits. Consequently, this shift disrupts endothelial cell junctions, increases vascular permeability, and exacerbates inflammation, creating a self-perpetuating cycle that drives atherosclerotic progression. While endothelial cell dysfunction initiates the development of atherosclerosis, autophagy, a cellular catabolic process designed to safeguard cells by recycling intracellular molecules, is believed to exert a significant role in plaque development. Identifying the pathological mechanisms and molecular mediators of EndoMT underpinning endothelial autophagy, may be of clinical relevance. Here, we offer new insights into the underlying biology of atherosclerosis and present potential molecular mechanisms of atherosclerotic resistance and highlight potential therapeutic targets.

Cellular Transdifferentiation: A Crucial Mechanism of Fibrosis in Systemic Sclerosis

Systemic Sclerosis (SSc) is a systemic autoimmune disease of unknown etiology with a highly complex pathogenesis that despite extensive investigation is not completely understood. The clinical and pathologic manifestations of the disease result from three distinct processes: 1) Severe and frequently progressive tissue fibrosis causing exaggerated and deleterious accumulation of interstitial collagens and other extracellular matrix molecules in the skin and various internal organs; 2) extensive fibroproliferative vascular lesions affecting small arteries and arterioles causing tissue ischemic alterations; and 3) cellular and humoral immunity abnormalities with the production of numerous autoantibodies, some with very high specificity for SSc. The fibrotic process in SSc is one of the main causes of disability and high mortality of the disease. Owing to its essentially universal presence and the severity of its clinical effects, the mechanisms involved in the development and progression of tissue fibrosis have been extensively investigated, however, despite intensive investigation, the precise molecular mechanisms have not been fully elucidated. Several recent studies have suggested that cellular transdifferentiation resulting in the phenotypic conversion of various cell types into activated myofibroblasts may be one important mechanism. Here, we review the potential role that cellular transdifferentiation may play in the development of severe and often progressive tissue fibrosis in SSc.

Transcriptome analysis reveals molecular signature and cell-type difference of Homo sapiens endothelial-to-mesenchymal transition

Endothelial-to-mesenchymal transition (EndoMT), a specific form of epithelial-to-mesenchymal transition, drives a growing number of human (Homo sapiens) pathological conditions. This emerging knowledge opens a path to discovering novel therapeutic targets for many EndoMT-associated disorders. Here, we constructed an atlas of the endothelial-cell transcriptome and demonstrated EndoMT-induced global changes in transcriptional gene expression. Our gene ontology analyses showed that EndoMT could be a specific checkpoint for leukocyte chemotaxis, adhesion, and transendothelial migration. We also identified distinct gene expression signatures underlying EndoMT across arterial, venous, and microvascular endothelial cells. We performed protein-protein interaction network analyses, identifying a class of highly connected hub genes in endothelial cells from different vascular beds. Moreover, we found that the short-chain fatty acid acetate strongly inhibits the transcriptional program of EndoMT in endothelial cells from different vascular beds across tissues. Our results reveal the molecular signature and cell-type difference of EndoMT across distinct tissue- and vascular-bed-specific endothelial cells, providing a powerful discovery tool and resource value. These results suggest that therapeutically manipulating the endothelial transcriptome could treat an increasing number of EndoMT-associated pathological conditions.

Endothelial-to-mesenchymal transition: advances and controversies

Endothelial-to-mesenchymal transition (EndMT) is a physiological process that is equally important during development and under certain pathological conditions in adult tissues. The last decade has witnessed a remarkable explosion of information about EndMT from molecular mechanisms responsible for its development to its role in various disease processes. The emerging picture is that of a complex set of interactions that underly pathophysiological basis of some of the most deadly and intractable diseases. This mini review brings together recent advances and attempts to present a unified view of this complex field.

Association of genetically-predicted placental gene expression with adult blood pressure traits

OBJECTIVE

Blood pressure is a complex, polygenic trait, and the need to identify prehypertensive risks and new gene targets for blood pressure control therapies or prevention continues. We hypothesize a developmental origins model of blood pressure traits through the life course where the placenta is a conduit mediating genomic and nongenomic transmission of disease risk. Genetic control of placental gene expression has recently been described through expression quantitative trait loci (eQTL) studies which have identified associations with childhood phenotypes.

METHODS

We conducted a transcriptome-wide gene expression analysis estimating the predicted gene expression of placental tissue in adult individuals with genome-wide association study (GWAS) blood pressure summary statistics. We constructed predicted expression models of 15 154 genes from reference placenta eQTL data and investigated whether genetically-predicted gene expression in placental tissue is associated with blood pressure traits using published GWAS summary statistics. Functional annotation of significant genes was generated using FUMA.

RESULTS

We identified 18, 9, and 21 genes where predicted expression in placenta was significantly associated with systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse pressure (PP), respectively. There were 14 gene-tissue associations (13 unique genes) significant only in placenta.

CONCLUSIONS

In this meta-analysis using S-PrediXcan and GWAS summary statistics, the predicted expression in placenta of 48 genes was statistically significantly associated with blood pressure traits. Notable findings included the association of FGFR1 expression with increased SBP and PP. This evidence of gene expression variation in placenta preceding the onset of adult blood pressure phenotypes is an example of extreme preclinical biological changes which may benefit from intervention.

CD45 Is Sufficient to Initiate Endothelial-to-Mesenchymal Transition in Human Endothelial Cells-Brief Report

BACKGROUND

Endothelial-to-mesenchymal transition (EndMT) is a dynamic process in which endothelial cells acquire mesenchymal properties and in turn contribute to tissue remodeling and growth. Previously, we found EndMT associated with mitral valve adaptation after myocardial infarction. Furthermore, mitral valve endothelial cells collected at 6 months post-myocardial infarction expressed the pan-leukocyte marker CD45 and EndMT markers. Additionally, mitral valve endothelial cells induced to undergo EndMT with TGF (transforming growth factor)-β1 strongly coexpressed CD45 but not CD11b or CD14. Pharmacologic inhibition of the CD45 PTPase (protein tyrosine phosphatase) domain in mitral valve endothelial cells blocked TGFβ-induced EndMT. This prompted us to speculate that, downstream of TGFβ, CD45 induces EndMT.

METHODS

We activated the endogenous CD45 promoter in human endothelial colony forming cells (ECFCs) using CRISPR (cluster regularly interspaced short palindromic repeats)/inactive Cas9 (CRISPR-associated protein 9) transcriptional activation. Bulk RNA sequencing was performed on control ECFCs and CD45-positive ECFCs to identify transcriptomic changes. Three functional assays-cellular migration, collagen gel contraction, and transendothelial electrical resistance-were conducted to assess mesenchymal properties in CD45-positive ECFCs.

RESULTS

Activation of the endogenous CD45 promoter in ECFC and 3 additional sources of endothelial cells induced expression of several genes implicated in EndMT. In addition, CD45-positive ECFCs showed increased migration, a hallmark of EndMT, increased collagen gel contraction, a hallmark of mesenchymal cells, and decreased cell-cell barrier integrity, indicating reduced endothelial function.

CONCLUSIONS

CD45 is sufficient to incite an EndMT phenotype and acquisition of mesenchymal cell properties in normal human ECFCs. We speculate that CD45, through its C-terminal PTPase domain, initiates signaling events that drive EndMT.

The Role of Cytokines in Cholesterol Accumulation in Cells and Atherosclerosis Progression

Atherosclerosis is the most common cardiovascular disease and is the number one cause of death worldwide. Today, atherosclerosis is a multifactorial chronic inflammatory disease with an autoimmune component, accompanied by the accumulation of cholesterol in the vessel wall and the formation of atherosclerotic plaques, endothelial dysfunction, and chronic inflammation. In the process of accumulation of atherogenic lipids, cells of the immune system, such as monocytes, macrophages, dendritic cells, etc., play an important role, producing and/or activating the production of various cytokines—interferons, interleukins, chemokines. In this review, we have tried to summarize the most important cytokines involved in the processes of atherogenesis.

Deficiency of endothelial FGFR1 signaling via upregulation of ROCK2 activity aggravated ALI/ARDS

Vascular leakage and inflammation are pathological hallmarks of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Endothelial cells (ECs) serve as a semipermeable barrier and play a key role in disease progression. It is well known that fibroblast growth factor receptor 1 (FGFR1) is required for maintaining vascular integrity. However, how endothelial FGFR1 functions in ALI/ARDS remains obscure. Here, we revealed that conditional deletion of endothelial FGFR1 aggravated LPS-induced lung injury, including inflammation and vascular leakage. Inhibition of its downstream Rho-associated coiled-coil–forming protein kinase 2 (ROCK2) by AAV Vec-tie-shROCK2 or its selective inhibitor TDI01 effectively attenuated inflammation and vascular leakage in a mouse model. In vitro, TNFα-stimulated human umbilical vein endothelial cells (HUVECs) showed decreased FGFR1 expression and increased ROCK2 activity. Furthermore, knockdown of FGFR1 activated ROCK2 and thus promoted higher adhesive properties to inflammatory cells and higher permeability in HUVECs. TDI01 effectively suppressed ROCK2 activity and rescued the endothelial dysfunction. These data demonstrated that the loss of endothelial FGFR1 signaling mediated an increase in ROCK2 activity, which led to an inflammatory response and vascular leakage in vivo and in vitro. Moreover, inhibition of ROCK2 activity by TDI01 provided great value and shed light on clinical translation.

Targeting Epsins to Inhibit Fibroblast Growth Factor Signaling While Potentiating Transforming Growth Factor-β Signaling Constrains Endothelial-to-Mesenchymal Transition in Atherosclerosis

BACKGROUND

Epsin endocytic adaptor proteins are implicated in the progression of atherosclerosis; however, the underlying molecular mechanisms have not yet been fully defined. In this study, we determined how epsins enhance endothelial-to-mesenchymal transition (EndoMT) in atherosclerosis and assessed the efficacy of a therapeutic peptide in a preclinical model of this disease.

METHODS

Using single-cell RNA sequencing combined with molecular, cellular, and biochemical analyses, we investigated the role of epsins in stimulating EndoMT using knockout in Apoe-/- and lineage tracing/proprotein convertase subtilisin/kexin type 9 serine protease mutant viral-induced atherosclerotic mouse models. The therapeutic efficacy of a synthetic peptide targeting atherosclerotic plaques was then assessed in Apoe-/- mice.

RESULTS

Single-cell RNA sequencing and lineage tracing revealed that epsins 1 and 2 promote EndoMT and that the loss of endothelial epsins inhibits EndoMT marker expression and transforming growth factor-β signaling in vitro and in atherosclerotic mice, which is associated with smaller lesions in the Apoe-/- mouse model. Mechanistically, the loss of endothelial cell epsins results in increased fibroblast growth factor receptor-1 expression, which inhibits transforming growth factor-β signaling and EndoMT. Epsins directly bind ubiquitinated fibroblast growth factor receptor-1 through their ubiquitin-interacting motif, which results in endocytosis and degradation of this receptor complex. Consequently, administration of a synthetic ubiquitin-interacting motif-containing peptide atheroma ubiquitin-interacting motif peptide inhibitor significantly attenuates EndoMT and progression of atherosclerosis.

CONCLUSIONS

We conclude that epsins potentiate EndoMT during atherogenesis by increasing transforming growth factor-β signaling through fibroblast growth factor receptor-1 internalization and degradation. Inhibition of EndoMT by reducing epsin-fibroblast growth factor receptor-1 interaction with a therapeutic peptide may represent a novel treatment strategy for atherosclerosis.

The Interaction of Apelin and FGFR1 Ameliorated the Kidney Fibrosis through Suppression of TGFβ-Induced Endothelial-to-Mesenchymal Transition

Both epithelial-to-mesenchymal (EMT) and endothelial-to-mesenchymal (EndMT) transitions have shown to contribute to the development and progression of kidney fibrosis. It has been reported that apelin, a regulatory peptide, alleviates EMT by inhibiting the transforming growth factor β (TGFβ) pathway in renal diseases. Additionally, fibroblast growth factor receptor 1 (FGFR1) has been shown to be a key inhibitor of EndMT through suppression of the TGFβ/Smad pathway. In this study, we found that apelin and FGFR1 were spatially close to each other and that the apelin and FGFR1 complex displayed inhibitory effects on TGFβ/Smad signaling as well as associated EndMT in diabetic kidney fibrosis. In cultured human dermal microvascular endothelial cells (HMVECs), we found that the anti-EndMT and anti-TGFβ/Smad effects of apelin were dampened in FGFR1-deficient cells. Either siRNA- or an inhibitor-mediated deficiency of apelin induced the Smad3 phosphorylation and EndMT. Streptozotocin-induced CD-1 diabetic mice displayed EndMT and associated kidney fibrosis, which were restored by apelin treatment. The medium from apelin-deficient endothelial cells stimulated TGFβ/Smad-dependent EMT in cultured HK2 cells. In addition, depletion of apelin and the FGFR1 complex impaired CEBPA expression, and TGFβ-induced repression of CEBPA expression contributed to the initiation of EndMT in the endothelium. Collectively, these findings revealed that the interaction between apelin and FGFR1 displayed renoprotective potential through suppression of the TGFβ/Smad/CEBPA-mediated EndMT/EMT pathways.

Translational opportunities of single-cell biology in atherosclerosis

The advent of single-cell biology opens a new chapter for understanding human biological processes and for diagnosing, monitoring, and treating disease. This revolution now reaches the field of cardiovascular disease (CVD). New technologies to interrogate CVD samples at single-cell resolution are allowing the identification of novel cell communities that are important in shaping disease development and direct towards new therapeutic strategies. These approaches have begun to revolutionize atherosclerosis pathology and redraw our understanding of disease development. This review discusses the state-of-the-art of single-cell analysis of atherosclerotic plaques, with a particular focus on human lesions, and presents the current resolution of cellular subpopulations and their heterogeneity and plasticity in relation to clinically relevant features. Opportunities and pitfalls of current technologies as well as the clinical impact of single-cell technologies in CVD patient care are highlighted, advocating for multidisciplinary and international collaborative efforts to join the cellular dots of CVD.

Smad3 promotes adverse cardiovascular remodeling and dysfunction in doxorubicin-treated hearts

Many anticancer therapies cause serious cardiovascular complications that degrade quality of life and cause early mortality in treated patients. Specifically, doxorubicin is known as an effective anticancer agent that causes cardiomyopathy in treated patients. There has been growing interest in defining the role of endothelial cells in cardiac damage by doxorubicin. We have shown in the present study that endothelial nuclei accumulate more intravenously administered doxorubicin than other cardiac cell types. Doxorubicin enhanced cardiac production of the transforming growth factor-β (TGF-β) ligands and nuclear translocation of phospho-Smad3 in both cultured and in vivo cardiac endothelial cells. To examine the role of the TGF-β/mothers against decapentaplegic homolog 3 (Smad3) pathway in cardiac damage by doxorubicin, we used both Smad3 shRNA stable endothelial cell lines and Smad3-knockout mice. We demonstrated using endothelial transcriptome analysis that upregulation of the TGF-β and inflammatory cytokine/cytokine receptor pathways, as well as suppression of cell cycle and angiogenesis by doxorubicin, were alleviated in Smad3-deficient endothelial cells. The results of transcriptomic analysis were validated using qPCR, immunoblotting, and ex vivo aortic ring sprouting assays. Similarly, increased cardiac expression of cytokines and chemokines observed in treated wild-type mice was diminished in treated Smad3-knockout animals. We also detected increased end-diastolic diameter and depressed systolic function in doxorubicin-treated wild-type but not Smad3-knockout mice. This work provides evidence for the critical role of the canonical TGF-β/Smad3 pathway in cardiac damage by doxorubicin.NEW & NOTEWORTHY Microvascular endothelial cells in the heart accumulate more intravenously administered doxorubicin than nonendothelial cardiac cell types. The treatment enhanced the TGF-β/Smad3 pathway and elicited endothelial cell senescence and inflammatory responses followed by adverse cardiac remodeling and dysfunction in wild-type but not Smad3-deficient animals. Our study suggests that the TGF-β/Smad3 pathway contributes to the development of doxorubicin cardiomyopathy and the potential value of novel approaches to ameliorate cardiotoxicity by targeting the Smad3 transcription factor.

Cellular phenotypic transitions in diabetic nephropathy: An update

Diabetic nephropathy (DN) is a major cause of morbidity and mortality in diabetes and is the most common cause of end stage renal disease (ESRD). Renal fibrosis is the final pathological change in DN. It is widely believed that cellular phenotypic switching is the cause of renal fibrosis in diabetic nephropathy. Several types of kidney cells undergo activation and differentiation and become reprogrammed to express markers of mesenchymal cells or podocyte-like cells. However, the development of targeted therapy for DN has not yet been identified. Here, we discussed the pathophysiologic changes of DN and delineated the possible origins that contribute to myofibroblasts and podocytes through phenotypic transitions. We also highlight the molecular signaling pathways involved in the phenotypic transition, which would provide valuable information for the activation of phenotypic switching and designing effective therapies for DN.

NLRP3-mediated pyroptosis in diabetic nephropathy

Diabetic nephropathy (DN) is the main cause of end-stage renal disease (ESRD), which is characterized by a series of abnormal changes such as glomerulosclerosis, podocyte loss, renal tubular atrophy and excessive deposition of extracellular matrix. Simultaneously, the occurrence of inflammatory reaction can promote the aggravation of DN-induced kidney injury. The most important processes in the canonical inflammasome pathway are inflammasome activation and membrane pore formation mediated by gasdermin family. Converging studies shows that pyroptosis can occur in renal intrinsic cells and participate in the development of DN, and its activation mechanism involves a variety of signaling pathways. Meanwhile, the activation of the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome can not only lead to the occurrence of inflammatory response, but also induce pyroptosis. In addition, a number of drugs targeting pyroptosis-associated proteins have been shown to have potential for treating DN. Consequently, the pathogenesis of pyroptosis and several possible activation pathways of NLRP3 inflammasome were reviewed, and the potential drugs used to treat pyroptosis in DN were summarized in this review. Although relevant studies are still not thorough and comprehensive, these findings still have certain reference value for the understanding, treatment and prognosis of DN.

Loss of α7nAChR enhances endothelial-to-mesenchymal transition after myocardial infarction via NF-κB activation

The myocardial fibrosis in response to myocardial infarction (MI) is closely related to the dysbalance of endothelial-to-mesenchymal transition (EndMT). Although numerous reports indicate that α7 nicotinic acetylcholine receptor (α7nAChR) activates the cholinergic anti-inflammatory pathway (CAP) to regulate the magnitude of inflammatory responses, the role of α7nAChR in myocardial fibrosis, as well as the underlying mechanisms, have not been elucidated. In this study, we evaluated cardiac function, fibrosis, and EndMT signaling using a mouse model of MI and interleukin (IL)-1β-induced human cardiac microvascular endothelial cells (HCMECs). In vivo, α7nAChR deletion increased cardiac dysfunction, exacerbated the cardiac inflammatory response, and NF-κB activation, and enhanced EndMT, as shown by higher expression levels of fibroblast markers (FSP-1, α-SMA, collagen I, Snail) and decreased levels of the FGFR1, glucocorticoid receptor (GR) and endothelial marker (CD31) compared to wild-type mice. In vitro, the pharmacological activation of α7nAChR with PNU282987 significantly inhibited IL-1β-induced EndMT, as shown by a reduced transition to the fibroblast-like phenotype and the expression of fibrotic markers. Moreover, the IL-1β-mediated activation of NF-κB pathway was suppressed by PNU282987. This anti-EndMT effect of α7nAChR was associated with regulation of Snail. Furthermore, Western blot analysis further revealed that the GR antagonist RU38486 could partially counteract the effect of PNU282987 on NF-κB expression. In conclusion, our results show that α7nAChR is involved in cardiac fibrosis by inhibiting EndMT, providing a novel approach to the treatment of MI.

Transforming growth factor-β-induced secretion of extracellular vesicles from oral cancer cells evokes endothelial barrier instability via endothelial-mesenchymal transition

Background

During metastasis, cancer cells undergo epithelial-mesenchymal transition (EMT) in response to transforming growth factor-β (TGF-β), which is abundant in the tumor microenvironment, and acquire invasive and metastatic potentials. Metastasis to distant organs requires intravascular invasion and extravasation of cancer cells, which is accompanied by the disruption of the adhesion between vascular endothelial cells. Cancer cell-derived extracellular vesicles (EVs) have been suggested to induce the destabilization of normal blood vessels at the metastatic sites. However, the roles of EVs secreted from cancer cells that have undergone EMT in the destabilization of blood vessels remain to be elucidated. In the present study, we characterized EVs secreted by oral cancer cells undergoing TGF-β-induced EMT and elucidated their effects on the characteristics of vascular endothelial cells.

Methods

Induction of EMT by TGF-β in human oral cancer cells was assessed using quantitative RT-PCR (qRT-PCR) and immunocytochemistry. Oral cancer cell-derived EVs were isolated from the conditioned media of oral cancer cells that were treated with or without TGF-β using ultracentrifugation, and characterized using nanoparticle tracking analysis and immunoblotting. The effects of EVs on human umbilical artery endothelial cells were examined by qRT-PCR, cellular staining, and permeability assay. The significant differences between means were determined using a t-test or one-way analysis of variance with Tukey’s multiple comparisons test.

Results

Oral cancer cells underwent EMT in response to TGF-β as revealed by changes in the expression of epithelial and mesenchymal cell markers at both the RNA and protein levels. Oral cancer cells treated with TGF-β showed increased EV production and altered EV composition when compared with untreated cells. The EVs that originated from cells that underwent EMT by TGF-β induced endothelial-mesenchymal transition, which was characterized by the decreased and increased expression of endothelial and mesenchymal cell markers, respectively. EVs derived from oral cancer cells also induced intercellular gap formation which led to the loss of endothelial cell barrier stability.

Conclusions

EVs released from oral cancer cells that underwent TGF-β-induced EMT target endothelial cells to induce vascular destabilization. Detailed characterization of oral cancer-derived EVs and factors responsible for EV-mediated vascular instability will lead to the development of agents targeting metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41232-022-00225-7.

Functions of exogenous FGF signals in regulation of fibroblast to myofibroblast differentiation and extracellular matrix protein expression

Fibroblasts are widely distributed cells found in most tissues and upon tissue injury, they are able to differentiate into myofibroblasts, which express abundant extracellular matrix (ECM) proteins. Overexpression and unordered organization of ECM proteins cause tissue fibrosis in damaged tissue. Fibroblast growth factor (FGF) family proteins are well known to promote angiogenesis and tissue repair, but their activities in fibroblast differentiation and fibrosis have not been systematically reviewed. Here we summarize the effects of FGFs in fibroblast to myofibroblast differentiation and ECM protein expression and discuss the underlying potential regulatory mechanisms, to provide a basis for the clinical application of recombinant FGF protein drugs in treatment of tissue damage.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

The Vascular Niche for Adult Cardiac Progenitor Cells

Research on cardiac progenitor cell populations has generated expectations about their potential for cardiac regeneration capacity after acute myocardial infarction and during physiological aging; however, the endogenous capacity of the adult mammalian heart is limited. The modest efficacy of exogenous cell-based treatments can guide the development of new approaches that, alone or in combination, can be applied to boost clinical efficacy. The identification and manipulation of the adult stem cell environment, termed niche, will be critical for providing new evidence on adult stem cell populations and improving stem-cell-based therapies. Here, we review and discuss the state of our understanding of the interaction of adult cardiac progenitor cells with other cardiac cell populations, with a focus on the description of the B-CPC progenitor population (Bmi1+ cardiac progenitor cell), which is a strong candidate progenitor for all main cardiac cell lineages, both in the steady state and after cardiac damage. The set of all interactions should be able to define the vascular cardiac stem cell niche, which is associated with low oxidative stress domains in vasculature, and whose manipulation would offer new hope in the cardiac regeneration field.

Endothelial Cell Phenotype, a Major Determinant of Venous Thrombo-Inflammation

Reduced blood flow velocity in the vein triggers inflammation and is associated with the release into the extracellular space of alarmins or damage-associated molecular patterns (DAMPs). These molecules include extracellular nucleic acids, extracellular purinergic nucleotides (ATP, ADP), cytokines and extracellular HMGB1. They are recognized as a danger signal by immune cells, platelets and endothelial cells. Hence, endothelial cells are capable of sensing environmental cues through a wide variety of receptors expressed at the plasma membrane. The endothelium is then responding by expressing pro-coagulant proteins, including tissue factor, and inflammatory molecules such as cytokines and chemokines involved in the recruitment and activation of platelets and leukocytes. This ultimately leads to thrombosis, which is an active pro-inflammatory process, tightly regulated, that needs to be properly resolved to avoid further vascular damages. These mechanisms are often dysregulated, which promote fibrinolysis defects, activation of the immune system and irreversible vascular damages further contributing to thrombotic and inflammatory processes. The concept of thrombo-inflammation is now widely used to describe the complex interactions between the coagulation and inflammation in various cardiovascular diseases. In endothelial cells, activating signals converge to multiple intracellular pathways leading to phenotypical changes turning them into inflammatory-like cells. Accumulating evidence suggest that endothelial to mesenchymal transition (EndMT) may be a major mechanism of endothelial dysfunction induced during inflammation and thrombosis. EndMT is a biological process where endothelial cells lose their endothelial characteristics and acquire mesenchymal markers and functions. Endothelial dysfunction might play a central role in orchestrating and amplifying thrombo-inflammation thought induction of EndMT processes. Mechanisms regulating endothelial dysfunction have been only partially uncovered in the context of thrombotic diseases. In the present review, we focus on the importance of the endothelial phenotype and discuss how endothelial plasticity may regulate the interplay between thrombosis and inflammation. We discuss how the endothelial cells are sensing and responding to environmental cues and contribute to thrombo-inflammation with a particular focus on venous thromboembolism (VTE). A better understanding of the precise mechanisms involved and the specific role of endothelial cells is needed to characterize VTE incidence and address the risk of recurrent VTE and its sequelae.

Tenascin-X Mediates Flow-Induced Suppression of EndMT and Atherosclerosis

BACKGROUND

Endothelial-to-mesenchymal transition (EndMT) has been identified as a critical driver of vascular inflammation and atherosclerosis, and TGF-β (transforming growth factor β) is a key mediator of EndMT. Both EndMT and atherosclerosis are promoted by disturbed flow, whereas unidirectional laminar flow limits EndMT and is atheroprotective. How EndMT and endothelial TGF-β signaling are regulated by different flow patterns is, however, still poorly understood.

METHODS

Flow chamber experiments in vitro and endothelium-specific knockout mice were used to study the role of tenascin-X in the regulation of EndMT and atherosclerosis as well as the underlying mechanisms.

RESULTS

In human endothelial cells as well as in human and mouse aortae, unidirectional laminar flow but not disturbed flow strongly increased endothelial expression of the extracellular matrix protein TN-X (tenascin-X) in a KLF4 (Krüppel-like factor 4) dependent manner. Mice with endothelium-specific loss of TN-X (EC-Tnxb-KO) showed increased endothelial TGF-β signaling as well as increased endothelial expression of EndMT and inflammatory marker genes. When EC-Tnxb-KO mice were subjected to partial carotid artery ligation, we observed increased vascular remodeling. EC-Tnxb-KO mice crossed to low-density lipoprotein receptor-deficient mice showed advanced atherosclerotic lesions after being fed a high-fat diet. Treatment of EC-Tnxb-KO mice with an anti-TGF-beta antibody or additional endothelial loss of TGF-beta receptors 1 and 2 normalized endothelial TGF-beta signaling and prevented EndMT. In in vitro studies, we found that TN-X through its fibrinogen-like domain directly interacts with TGF-β and thereby interferes with its binding to the TGF-β receptor.

CONCLUSIONS

In summary, we show that TN-X is a central mediator of flow-induced inhibition of EndMT, endothelial inflammation and atherogenesis, which functions by binding to and by blocking the activity of TGF-β. Our data identify a novel mechanism of flow-dependent regulation of vascular TGF-β, which holds promise for generating new strategies to prevent vascular inflammation and atherosclerosis.

Endothelial OCT4 is atheroprotective by preventing metabolic and phenotypic dysfunction

AIMS

Until recently, the pluripotency factor Octamer (ATGCAAAT)-binding transcriptional factor 4 (OCT4) was believed to be dispensable in adult somatic cells. However, our recent studies provided clear evidence that OCT4 has a critical atheroprotective role in smooth muscle cells. Here, we asked if OCT4 might play a functional role in regulating endothelial cell (EC) phenotypic modulations in atherosclerosis.

METHODS AND RESULTS

Specifically, we show that EC-specific Oct4 knockout resulted in increased lipid, LGALS3+ cell accumulation, and altered plaque characteristics consistent with decreased plaque stability. A combination of single-cell RNA sequencing and EC-lineage-tracing studies revealed increased EC activation, endothelial-to-mesenchymal transitions, plaque neovascularization, and mitochondrial dysfunction in the absence of OCT4. Furthermore, we show that the adenosine triphosphate (ATP) transporter, ATP-binding cassette (ABC) transporter G2 (ABCG2), is a direct target of OCT4 in EC and establish for the first time that the OCT4/ABCG2 axis maintains EC metabolic homeostasis by regulating intracellular heme accumulation and related reactive oxygen species production, which, in turn, contributes to atherogenesis.

CONCLUSIONS

These results provide the first direct evidence that OCT4 has a protective metabolic function in EC and identifies vascular OCT4 and its signalling axis as a potential target for novel therapeutics.

MEKK3-TGFβ crosstalk regulates inward arterial remodeling

Arterial remodeling is an important adaptive mechanism that maintains normal fluid shear stress in a variety of physiologic and pathologic conditions. Inward remodeling, a process that leads to reduction in arterial diameter, plays a critical role in progression of such common diseases as hypertension and atherosclerosis. Yet, despite its pathogenic importance, molecular mechanisms controlling inward remodeling remain undefined. Mitogen-activated protein kinases (MAPKs) perform a number of functions ranging from control of proliferation to migration and cell-fate transitions. While the MAPK ERK1/2 signaling pathway has been extensively examined in the endothelium, less is known about the role of the MEKK3/ERK5 pathway in vascular remodeling. To better define the role played by this signaling cascade, we studied the effect of endothelial-specific deletion of its key upstream MAP3K, MEKK3, in adult mice. The gene's deletion resulted in a gradual inward remodeling of both pulmonary and systematic arteries, leading to spontaneous hypertension in both vascular circuits and accelerated progression of atherosclerosis in hyperlipidemic mice. Molecular analysis revealed activation of TGFβ-signaling both in vitro and in vivo. Endothelial-specific TGFβR1 knockout prevented inward arterial remodeling in MEKK3 endothelial knockout mice. These data point to the unexpected participation of endothelial MEKK3 in regulation of TGFβR1-Smad2/3 signaling and inward arterial remodeling in artery diseases.

Endothelial to Mesenchymal Transition: An Insight in Atherosclerosis

Atherosclerosis is a fundamental disease of the cardiovascular system that leads to high morbidity and mortality worldwide. The endothelium is the first protective barrier in atherosclerosis. Endothelial cells have the potential to be transformed into mesenchymal cells, in a process termed endothelial to mesenchymal transition (EndMT). On the one hand, EndMT is known to contribute to atherosclerosis by inducing a number of phenotypes ranging from endothelial cell dysfunction to plaque formation. On the other hand, risk factors for atherosclerosis can lead to EndMT. A substantial body of evidence has suggested that EndMT induces the development of atherosclerosis; therefore, a deeper understanding of the molecular mechanisms underlying EndMT in atherosclerosis might provide insights to reverse this condition.

Endothelial-Mesenchymal Transition in Cardiovascular Disease

Endothelial-to-mesenchymal transition is a dynamic process in which endothelial cells suppress constituent endothelial properties and take on mesenchymal cell behaviors. To begin the process, endothelial cells loosen their cell-cell junctions, degrade the basement membrane, and migrate out into the perivascular surroundings. These initial endothelial behaviors reflect a transient modulation of cellular phenotype, that is, a phenotypic modulation, that is sometimes referred to as partial endothelial-to-mesenchymal transition. Loosening of endothelial junctions and migration are also seen in inflammatory and angiogenic settings such that endothelial cells initiating endothelial-to-mesenchymal transition have overlapping behaviors and gene expression with endothelial cells responding to inflammatory signals or sprouting to form new blood vessels. Reduced endothelial junctions increase permeability, which facilitates leukocyte trafficking, whereas endothelial migration precedes angiogenic sprouting and neovascularization; both endothelial barriers and quiescence are restored as inflammatory and angiogenic stimuli subside. Complete endothelial-to-mesenchymal transition proceeds beyond phenotypic modulation such that mesenchymal characteristics become prominent and endothelial functions diminish. In proadaptive, regenerative settings the new mesenchymal cells produce extracellular matrix and contribute to tissue integrity whereas in maladaptive, pathologic settings the new mesenchymal cells become fibrotic, overproducing matrix to cause tissue stiffness, which eventually impacts function. Here we will review what is known about how TGF (transforming growth factor) β influences this continuum from junctional loosening to cellular migration and its relevance to cardiovascular diseases.

Endothelial FGF signaling is protective in hypoxia-induced pulmonary hypertension

Hypoxia-induced pulmonary hypertension (PH) is one of the most common and deadliest forms of PH. Fibroblast growth factor receptors 1 and 2 (FGFR1/2) are elevated in patients with PH and in mice exposed to chronic hypoxia. Endothelial FGFR1/2 signaling is important for the adaptive response to several injury types and we hypothesized that endothelial FGFR1/2 signaling would protect against hypoxia-induced PH. Mice lacking endothelial FGFR1/2, mice with activated endothelial FGFR signaling, and human pulmonary artery endothelial cells (HPAECs) were challenged with hypoxia. We assessed the effect of FGFR activation and inhibition on right ventricular pressure, vascular remodeling, and endothelial-mesenchymal transition (EndMT), a known pathologic change seen in patients with PH. Hypoxia-exposed mice lacking endothelial FGFRs developed increased PH, while mice overexpressing a constitutively active FGFR in endothelial cells did not develop PH. Mechanistically, lack of endothelial FGFRs or inhibition of FGFRs in HPAECs led to increased TGF-β signaling and increased EndMT in response to hypoxia. These phenotypes were reversed in mice with activated endothelial FGFR signaling, suggesting that FGFR signaling inhibits TGF-β pathway-mediated EndMT during chronic hypoxia. Consistent with these observations, lung tissue from patients with PH showed activation of FGFR and TGF-β signaling. Collectively, these data suggest that activation of endothelial FGFR signaling could be therapeutic for hypoxia-induced PH.

Histone deacetylase 9 promotes endothelial-mesenchymal transition and an unfavorable atherosclerotic plaque phenotype

Endothelial-mesenchymal transition (EndMT) is associated with various cardiovascular diseases and in particular with atherosclerosis and plaque instability. However, the molecular pathways that govern EndMT are poorly defined. Specifically, the role of epigenetic factors and histone deacetylases (HDACs) in controlling EndMT and the atherosclerotic plaque phenotype remains unclear. Here, we identified histone deacetylation, specifically that mediated by HDAC9 (a class IIa HDAC), as playing an important role in both EndMT and atherosclerosis. Using in vitro models, we found class IIa HDAC inhibition sustained the expression of endothelial proteins and mitigated the increase in mesenchymal proteins, effectively blocking EndMT. Similarly, ex vivo genetic knockout of Hdac9 in endothelial cells prevented EndMT and preserved a more endothelial-like phenotype. In vivo, atherosclerosis-prone mice with endothelial-specific Hdac9 knockout showed reduced EndMT and significantly reduced plaque area. Furthermore, these mice displayed a more favorable plaque phenotype, with reduced plaque lipid content and increased fibrous cap thickness. Together, these findings indicate that HDAC9 contributes to vascular pathology by promoting EndMT. Our study provides evidence for a pathological link among EndMT, HDAC9, and atherosclerosis and suggests that targeting of HDAC9 may be beneficial for plaque stabilization or slowing the progression of atherosclerotic disease.

Endothelial to Mesenchymal Transition in the Cardiogenesis and Cardiovascular Diseases

Today, cardiovascular diseases remain a leading cause of morbidity and mortality worldwide. Endothelial to mesenchymal transition (EndMT) does not only play a major role in the course of development but also contributes to several cardiovascular diseases in adulthood. EndMT is characterized by down-regulation of the endothelial proteins and highly up-regulated fibrotic specific genes and extracellular matrix-forming proteins. EndMT is also a transforming growth factor-β-driven (TGF-β) process in which endothelial cells lose their endothelial characteristics and acquire a mesenchymal phenotype with expression of α-smooth muscle actin (α-SMA), fibroblast-specific protein 1, etc. EndMT is a vital process during cardiac development, thus disrupted EndMT gives rise to the congenital heart diseases, namely septal defects and valve abnormalities. In this review, we have discussed the main signaling pathways and mechanisms participating in the process of EndMT such as TGF-β and Bone morphogenetic protein (BMP), Wnt^#, and Notch signaling pathway and also studied the role of EndMT in physiological cardiovascular development and pathological conditions including myocardial infarction, pulmonary arterial hypertension, congenital heart defects, cardiac fibrosis, and atherosclerosis. As a perspective view, having a clear understanding of involving cellular and molecular mechanisms in EndMT and conducting Randomized controlled trials (RCTs) with a large number of samples for involving pharmacological agents may guide us into novel therapeutic approaches of congenital disorders and heart diseases.

Endothelial FGFR1 (Fibroblast Growth Factor Receptor 1) Deficiency Contributes Differential Fibrogenic Effects in Kidney and Heart of Diabetic Mice

Endothelial-to-mesenchymal transition (EndMT) has been shown to contribute to organ fibrogenesis. We have reported that N-acetyl-seryl-aspartyl- lysyl-proline (AcSDKP) restored levels of diabetes mellitus-suppressed FGFR1 (fibroblast growth factor receptor 1), the endothelial receptor essential for combating EndMT. However, the molecular regulation and biological/pathological significance of the AcSDKP-FGFR1 relationship has not been elucidated yet. Here, we demonstrated that endothelial FGFR1 deficiency led to AcSDKP-resistant EndMT and severe fibrosis associated with EndMT-stimulated fibrogenic programming in neighboring cells. Diabetes mellitus induced severe kidney fibrosis in endothelial FGFR1-deficient mice (FGFR1^fl/fl; VE-cadherin-Cre: FGFR1^EKO) but not in control mice (FGFR1^fl/fl); AcSDKP completely or partially suppressed kidney fibrosis in control or FGFR1^EKO mice. Severe fibrosis was also induced in hearts of diabetic FGFR1^EKO mice; however, AcSDKP had no effect on heart fibrosis in FGFR1^EKO mice. AcSDKP also had no effect on EndMT in either kidney or heart but partially suppressed epithelial-to-mesenchymal transition in kidneys of diabetic FGFR1^EKO mice. The medium from FGFR1-deficient endothelial cells stimulated TGFβ (transforming growth factor β)/Smad-dependent epithelial-to-mesenchymal transition in cultured human proximal tubule epithelial cell line, AcSDKP inhibited such epithelial-to-mesenchymal transition. These data demonstrated that endothelial FGFR1 is essential as an antifibrotic core molecule as the target of AcSDKP.

Non-coding RNA in endothelial-to-mesenchymal transition

Endothelial-to-mesenchymal transition (EndMT) is the process wherein endothelial cells lose their typical endothelial cell markers and functions and adopt a mesenchymal-like phenotype. EndMT is required for development of the cardiac valves, the pulmonary and dorsal aorta, and arterial maturation, but activation of the EndMT programme during adulthood is believed to contribute to several pathologies including organ fibrosis, cardiovascular disease, and cancer. Non-coding RNAs, including microRNAs, long non-coding RNAs, and circular RNAs, modulate EndMT during development and disease. Here, we review the mechanisms by which non-coding RNAs facilitate or inhibit EndMT during development and disease and provide a perspective on the therapeutic application of non-coding RNAs to treat fibroproliferative cardiovascular disease.

Therapeutic Angiogenesis Using HGF Plasmid

Hepatocyte growth factor (HGF) is secreted from stromal and mesenchymal cells, and its receptor cMet is expressed on various types of cells such as smooth muscle cells, fibroblast, and endothelial cells. HGF stimulates epithelial and endothelial cell proliferation, motility, and morphogenesis in a paracrine and autocrine manner, organizing multistep of angiogenesis in many organs. In addition, HGF is recognized as a potent anti-inflammatory and anti-fibrotic growth factor, which has been proved in several animal studies, including neointimal hyperplasia and acute myocardial infarction model in rodent. Thus, as compared to other angiogenic growth factors, HGF exerts multiple effects on ischemic tissues, accompanied by the regression of tissue inflammation and fibrosis. These data suggest the therapeutic potential of the HGF for peripheral artery disease as it being accompanied with chronic tissue inflammation and fibrosis. In the present narrative review, the pleiotropic action of the HGF that differentiates it from other angiogenic growth factors is discussed first, and later, outcomes of the human clinical study with gene therapy are overviewed.

N-acetyl-seryl-aspartyl-lysyl-proline is a valuable endogenous antifibrotic peptide for kidney fibrosis in diabetes: An update and translational aspects

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is an endogenous peptide that has been confirmed to show excellent organ-protective effects. Even though originally discovered as a modulator of hemotopoietic stem cells, during the recent two decades, AcSDKP has been recognized as valuable antifibrotic peptide. The antifibrotic mechanism of AcSDKP is not yet clear; we have established that AcSDKP could target endothelial-mesenchymal transition program through the induction of the endothelial fibroblast growth factor receptor signaling pathway. Also, recent reports suggested the clinical significance of AcSDKP. The aim of this review was to update recent advances of the mechanistic action of AcSDKP and discuss translational research aspects.

TGF-β-Induced Endothelial to Mesenchymal Transition in Disease and Tissue Engineering

Endothelial to mesenchymal transition (EndMT) is a complex biological process that gives rise to cells with multipotent potential. EndMT is essential for the formation of the cardiovascular system during embryonic development. Emerging results link EndMT to the postnatal onset and progression of fibrotic diseases and cancer. Moreover, recent reports have emphasized the potential for EndMT in tissue engineering and regenerative applications by regulating the differentiation status of cells. Transforming growth factor β (TGF-β) engages in many important physiological processes and is a potent inducer of EndMT. In this review, we first summarize the mechanisms of the TGF-β signaling pathway as it relates to EndMT. Thereafter, we discuss the pivotal role of TGF-β-induced EndMT in the development of cardiovascular diseases, fibrosis, and cancer, as well as the potential application of TGF-β-induced EndMT in tissue engineering.

The histone demethylase JMJD2B regulates endothelial-to-mesenchymal transition

Here we show that the histone demethylase JMJD2B is induced in endothelial cells by EndMT provoking stimuli and thereby contributes to the acquirement of a mesenchymal/smooth muscle phenotype. Silencing of JMJD2B inhibited EndMT in vitro and reduced the induction of EndMT after myocardial infarction in vivo. Inhibition of JMJD2B prevents the demethylation of repressive trimethylated histone H3 at lysine 9 (H3K9me3) at promoters of mesenchymal and EndMT-controlling genes, thereby reducing EndMT. Together, our study reports a crucial role for JMJD2B in controlling histone modifications during the transition of endothelial cells toward a mesenchymal phenotype.

Endothelial cells play an important role in maintenance of the vascular system and the repair after injury. Under proinflammatory conditions, endothelial cells can acquire a mesenchymal phenotype by a process named endothelial-to-mesenchymal transition (EndMT), which affects the functional properties of endothelial cells. Here, we investigated the epigenetic control of EndMT. We show that the histone demethylase JMJD2B is induced by EndMT-promoting, proinflammatory, and hypoxic conditions. Silencing of JMJD2B reduced TGF-β2-induced expression of mesenchymal genes, prevented the alterations in endothelial morphology and impaired endothelial barrier function. Endothelial-specific deletion of JMJD2B in vivo confirmed a reduction of EndMT after myocardial infarction. EndMT did not affect global H3K9me3 levels but induced a site-specific reduction of repressive H3K9me3 marks at promoters of mesenchymal genes, such as Calponin (CNN1), and genes involved in TGF-β signaling, such as AKT Serine/Threonine Kinase 3 (AKT3) and Sulfatase 1 (SULF1). Silencing of JMJD2B prevented the EndMT-induced reduction of H3K9me3 marks at these promotors and further repressed these EndMT-related genes. Our study reveals that endothelial identity and function is critically controlled by the histone demethylase JMJD2B, which is induced by EndMT-promoting, proinflammatory, and hypoxic conditions, and supports the acquirement of a mesenchymal phenotype.

Activated Endothelial TGFβ1 Signaling Promotes Venous Thrombus Nonresolution in Mice Via Endothelin-1: Potential Role for Chronic Thromboembolic Pulmonary Hypertension

RATIONALE

Chronic thromboembolic pulmonary hypertension (CTEPH) is characterized by defective thrombus resolution, pulmonary artery obstruction, and vasculopathy. TGFβ (transforming growth factor-β) signaling mutations have been implicated in pulmonary arterial hypertension, whereas the role of TGFβ in the pathophysiology of CTEPH is unknown.

OBJECTIVE

To determine whether defective TGFβ signaling in endothelial cells contributes to thrombus nonresolution and fibrosis.

METHODS AND RESULTS

Venous thrombosis was induced by inferior vena cava ligation in mice with genetic deletion of TGFβ1 in platelets (Plt.TGFβ-KO) or TGFβ type II receptors in endothelial cells (End.TGFβRII-KO). Pulmonary endarterectomy specimens from CTEPH patients were analyzed using immunohistochemistry. Primary human and mouse endothelial cells were studied using confocal microscopy, quantitative polymerase chain reaction, and Western blot. Absence of TGFβ1 in platelets did not alter platelet number or function but was associated with faster venous thrombus resolution, whereas endothelial TGFβRII deletion resulted in larger, more fibrotic and higher vascularized venous thrombi. Increased circulating active TGFβ1 levels, endothelial TGFβRI/ALK1 (activin receptor-like kinase), and TGFβRI/ALK5 expression were detected in End.TGFβRII-KO mice, and activated TGFβ signaling was present in vessel-rich areas of CTEPH specimens. CTEPH-endothelial cells and murine endothelial cells lacking TGFβRII simultaneously expressed endothelial and mesenchymal markers and transcription factors regulating endothelial-to-mesenchymal transition, similar to TGFβ1-stimulated endothelial cells. Mechanistically, increased endothelin-1 levels were detected in TGFβRII-KO endothelial cells, murine venous thrombi, or endarterectomy specimens and plasma of CTEPH patients, and endothelin-1 overexpression was prevented by inhibition of ALK5, and to a lesser extent of ALK1. ALK5 inhibition and endothelin receptor antagonization inhibited mesenchymal lineage conversion in TGFβ1-exposed human and murine endothelial cells and improved venous thrombus resolution and pulmonary vaso-occlusions in End.TGFβRII-KO mice.

CONCLUSIONS

Endothelial TGFβ1 signaling via type I receptors and endothelin-1 contribute to mesenchymal lineage transition and thrombofibrosis, which were prevented by blocking endothelin receptors. Our findings may have relevant implications for the prevention and management of CTEPH.

FRS2α-dependent cell fate transition during endocardial cushion morphogenesis

Atrioventricular valve development requires endothelial-to-mesenchymal transition (EndMT) that induces cushion endocardial cells to give rise to mesenchymal cells crucial to valve formation. In the adult endothelium, deletion of the docking protein FRS2α induces EndMT by activating TGFβ signaling in a miRNA let-7-dependent manner. To study the role of endothelial FRS2α during embryonic development, we generated mice with an inducible endothelial-specific deletion of Frs2α (FRS2α^iECKO). Analysis of the FRS2α^iECKO embryos uncovered a combination of impaired EndMT in AV cushions and defective maturation of AV valves leading to development of thickened, abnormal valves when Frs2α was deleted early (E7.5) in development. At the same time, no AV valve developmental abnormalities were observed after late (E10.5) deletion. These observations identify FRS2α as a pivotal controller of cell fate transition during both EndMT and post-EndMT valvulogenesis.

Regulation of Endothelial-to-Mesenchymal Transition by MicroRNAs in Chronic Allograft Dysfunction

Fibrosis is a universal finding in chronic allograft dysfunction, and it is characterized by an accumulation of extracellular matrix. The precise source of the myofibroblasts responsible for matrix deposition is not understood, and pharmacological strategies for prevention or treatment of fibrosis remain limited. One source of myofibroblasts in fibrosis is an endothelial-to-mesenchymal transition (EndMT), a process first described in heart development and involving endothelial cells undergoing a phenotypic change to become more like mesenchymal cells. Recently, lineage tracing of endothelial cells in mouse models allowed studies of EndMT in vivo and reported 27% to 35% of myofibroblasts involved in cardiac fibrosis and 16% of isolated fibroblasts in bleomycin-induced pulmonary fibrosis to be of endothelial origin. Over the past decade, mature microRNAs (miRNAs) have increasingly been described as key regulators of biological processes through repression or degradation of targeted mRNA. The stability and abundance of miRNAs in body fluids make them attractive as potential biomarkers, and progress is being made in developing miRNA targeted therapeutics. In this review, we will discuss the evidence of miRNA regulation of EndMT from in vitro and in vivo studies and the potential relevance of this to heart, lung, and kidney allograft dysfunction.

microRNA Crosstalk Influences Epithelial-to-Mesenchymal, Endothelial-to-Mesenchymal, and Macrophage-to-Mesenchymal Transitions in the Kidney

microRNAs (miRNAs) are small, non-coding nucleotides that regulate diverse biological processes. Altered microRNA biosynthesis or regulation contributes to pathological processes including kidney fibrosis. Kidney fibrosis is characterized by deposition of excess extracellular matrix (ECM), which is caused by infiltration of immune cells, inflammatory cells, altered chemokines, and cytokines as well as activation and accumulation of fibroblasts in the kidney. These activated fibroblasts can arise from epithelial cells via epithelial-to-mesenchymal transition (EMT), from bone marrow-derived M2 phenotype macrophages via macrophage-to-mesenchymal transition (MMT), from endothelial cells via endothelial-to-mesenchymal transition (EndMT), from resident fibroblasts, and from bone marrow-derived monocytes and play a crucial role in fibrotic events. Disrupted microRNA biosynthesis and aberrant regulation contribute to the activation of mesenchymal programs in the kidney. miR-29 regulates the interaction between dipeptidyl peptidase-4 (DPP-4) and integrin β1 and the associated active transforming growth factor β (TGFβ) and pro-EndMT signaling; however, miR-let-7 targets transforming growth factor β receptors (TGFβRs) to inhibit TGFβ signaling. N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is an endogenous anti-fibrotic peptide, which is associated with fibroblast growth factor receptor 1 (FGFR1) phosphorylation and subsequently responsible for the production of miR-let-7. miR-29 and miR-let-7 family clusters participate in crosstalk mechanisms, which are crucial for endothelial cell homeostasis. The physiological level of AcSDKP is vital for the activation of anti-fibrotic mechanisms including restoration of anti-fibrotic microRNA crosstalk and suppression of profibrotic signaling by mitigating DPP-4-associated mesenchymal activation in the epithelial cells, endothelial cells, and M2 phenotype macrophages. The present review highlights recent advancements in the understanding of both the role of microRNAs in the development of kidney disease and their potential as novel therapeutic targets for fibrotic disease states.

Fibroblast growth factor signals regulate transforming growth factor-β-induced endothelial-to-myofibroblast transition of tumor endothelial cells via Elk1

The tumor microenvironment contains various components, including cancer cells, tumor vessels, and cancer-associated fibroblasts, the latter of which are comprised of tumor-promoting myofibroblasts and tumor-suppressing fibroblasts. Multiple lines of evidence indicate that transforming growth factor-β (TGF-β) induces the formation of myofibroblasts and other types of mesenchymal (non-myofibroblastic) cells from endothelial cells. Recent reports show that fibroblast growth factor 2 (FGF2) modulates TGF-β-induced mesenchymal transition of endothelial cells, but the molecular mechanisms behind the signals that control transcriptional networks during the formation of different groups of fibroblasts remain largely unclear. Here, we studied the roles of FGF2 during the regulation of TGF-β-induced mesenchymal transition of tumor endothelial cells (TECs). We demonstrated that auto/paracrine FGF signals in TECs inhibit TGF-β-induced endothelial-to-myofibroblast transition (End-MyoT), leading to suppressed formation of contractile myofibroblast cells, but on the other hand can also collaborate with TGF-β in promoting the formation of active fibroblastic cells which have migratory and proliferative properties. FGF2 modulated TGF-β-induced formation of myofibroblastic and non-myofibroblastic cells from TECs via transcriptional regulation of various mesenchymal markers and growth factors. Furthermore, we observed that TECs treated with TGF-β were more competent in promoting in vivo tumor growth than TECs treated with TGF-β and FGF2. Mechanistically, we showed that Elk1 mediated FGF2-induced inhibition of End-MyoT via inhibition of TGF-β-induced transcriptional activation of α-smooth muscle actin promoter by myocardin-related transcription factor-A. Our data suggest that TGF-β and FGF2 oppose and cooperate with each other during the formation of myofibroblastic and non-myofibroblastic cells from TECs, which in turn determines the characteristics of mesenchymal cells in the tumor microenvironment.

FGF signaling contributes to atherosclerosis by enhancing the inflammatory response in vascular smooth muscle cells

The contractile to synthetic phenotypic switching of vascular smooth muscle cells (VSMCs) in response to fibroblast growth factor (FGF) has been previously described. However, the role of the inflammatory response induced by FGF signaling in VSMCs and its occurrence in atherosclerosis remains unclear. In the present study, FGF signaling promoted a contractile to secretory phenotypic transition in VSMCs. VSMCs (primary human aortic smooth muscle cells) treated with FGF exhibited a decrease in the protein expression levels of factors involved in contractility and the secretion of various chemokines was increased, as assessed by reverse transcription-quantitative PCR and ELISA. Additionally, inhibition of FGF signaling by silencing FGF receptor substrate 2 (FRS2) decreased the protein expression levels of various chemokines. Furthermore, VSMCs in the medial layers of arteries from apolipoprotein E-deficient mice and human atherosclerotic samples exhibited an increase in FGF signaling that was identified to be associated with an increase in the protein expression levels of pro-inflammatory molecules, including C-C motif chemokine ligand 2, C-X-C motif chemokine ligand (CXCL) 9, CXCL10 and CXCL11, compared with wild-type mice and healthy control samples, respectively. The present results suggested that FGF signaling induced dedifferentiation of contractile VSMCs and the transition to a secretory phenotype, which may be involved in the progression of atherosclerosis. Collectively, the present results suggested that the FGF signaling pathway may represent a novel target for the treatment of atherosclerosis.

βklotho is essential for the anti-endothelial mesenchymal transition effects of N-acetyl-seryl-aspartyl-lysyl-proline

Endothelial–mesenchymal transition (EndMT) has emerged as an essential bioprocess responsible for the development of organ fibrosis. We have previously reported that fibroblast growth factor receptor 1 (FGFR1) is involved in the anti‐EndMT effect of N‐acetyl‐seryl‐aspartyl‐lysyl‐proline (AcSDKP). FGFR1 is expressed on the cell membrane and performs its biological function through interaction with co‐receptors, including βklotho (KLB). However, it remains unknown whether KLB is involved in the anti‐EndMT effects of AcSDKP. Here, we demonstrated that AcSDKP increased KLB expression in an FGFR1‐dependent manner and that KLB deficiency induced AcSDKP‐resistant EndMT via the induction of the mitogen‐activated protein kinase (MAPK) pathway. In cultured endothelial cells, AcSDKP increased KLB protein level in an FGFR1‐dependent manner through induction of the FGFR1–KLB complex. KLB suppression by small interfering RNA transfection did not affect FGFR1 levels and resulted in the induction of EndMT. In contrast to the EndMT observed under FGFR1 deficiency, the EndMT induced by KLB suppression was not accompanied by the induction of Smad3 phosphorylation; instead, KLB‐deficient cells exhibited induced activation of the MAPK/extracellular signal‐regulated kinase (ERK) kinase (MEK) and ERK pathways. Treatment with the specific MEK inhibitor U0126 diminished KLB deficiency‐induced EndMT. Consistent with this finding, AcSDKP did not suppress either EndMT or MEK/ERK activation induced by KLB deficiency. Application of either FGF19 or FGF21 synergistically augmented the anti‐EndMT effects of AcSDKP. Taken together, these results indicate that endogenous peptide AcSDKP exerts its activity through induction of the FGFR1–KLB complex in vascular endothelial cells.

Endothelial to Mesenchymal Transition: Role in Physiology and in the Pathogenesis of Human Diseases

Numerous studies have demonstrated that endothelial cells are capable of undergoing endothelial to mesenchymal transition (EndMT), a newly recognized type of cellular transdifferentiation. EndMT is a complex biological process in which endothelial cells adopt a mesenchymal phenotype displaying typical mesenchymal cell morphology and functions, including the acquisition of cellular motility and contractile properties. Endothelial cells undergoing EndMT lose the expression of endothelial cell-specific proteins such as CD31/platelet-endothelial cell adhesion molecule, von Willebrand factor, and vascular-endothelial cadherin and initiate the expression of mesenchymal cell-specific genes and the production of their encoded proteins including α-smooth muscle actin, extra domain A fibronectin, N-cadherin, vimentin, fibroblast specific protein-1, also known as S100A4 protein, and fibrillar type I and type III collagens. Transforming growth factor-β1 is considered the main EndMT inducer. However, EndMT involves numerous molecular and signaling pathways that are triggered and modulated by multiple and often redundant mechanisms depending on the specific cellular context and on the physiological or pathological status of the cells. EndMT participates in highly important embryonic development processes, as well as in the pathogenesis of numerous genetically determined and acquired human diseases including malignant, vascular, inflammatory, and fibrotic disorders. Despite intensive investigation, many aspects of EndMT remain to be elucidated. The identification of molecules and regulatory pathways involved in EndMT and the discovery of specific EndMT inhibitors should provide novel therapeutic approaches for various human disorders mediated by EndMT.

Targeting endothelial-to-mesenchymal transition: the protective role of hydroxytyrosol sulfate metabolite

PURPOSE

Endothelial-to-mesenchymal transition (EndMT) plays an important role in pathogenesis of a number of inflammatory diseases. Hydroxytyrosol (HT) and, particularly, its major plasma metabolite HT-3O sulfate (HT-3Os) are known olive oil antioxidant and anti-inflammatory polyphenols which exert benefits against vascular diseases by improving endothelial function. However, to date the HT-3Os role in EndMT is not well known.

METHODS

To investigate the HT-3Os effects on EndMT in the inflamed endothelium, we used an in vitro model of endothelial dysfunction, challenging endothelial cells (EC), human umbilical EC (HUVEC) and human retinal EC (HREC) with Interleukin-1β (IL-1β), an inflammatory agent. HREC were used as a specific model to investigate HT-3Os effects on vascular retinal diseases.

RESULTS

We found that IL-1β treatment-induced EndMT phenotype in both cell models, also changing cell morphology. HT-3Os protected EC against IL-1β effects, recovering cell morphology and phenotype. Mechanistically, HT-3Os targeting fibroblast growth factor receptor 1 FGFR1 expression and let-7 miRNA, controlled transforming growth factor beta (TGF-β) signalling in EC, downregulating transcription factors expression (SNAI1 and ZEB2) and gene expression of late EndMT markers (FN1, VIM, NOTCH3, CNN1, MMP2 and MMP9).

CONCLUSION

These results demonstrate that HT-3Os blunts pathological EndMT in inflamed EC, maintaining high let-7 miRNA expression and preventing activation of TGF-β signalling.

GSK-3β regulates the endothelial-to-mesenchymal transition via reciprocal crosstalk between NSCLC cells and HUVECs in multicellular tumor spheroid models

BACKGROUND

Chemotherapy used for patients with unresectable lung tumors remains largely palliative due to chemoresistance, which may be due to tumor heterogeneity. Recently, multiple studies on the crosstalk between lung cancer cells and their tumor microenvironment (TME) have been conducted to understand and overcome chemoresistance in lung cancer.

METHODS

In this study, we investigated the effect of reciprocal crosstalk between lung cancer cells and vascular endothelial cells using multicellular tumor spheroids (MCTSs) containing lung cancer cells and HUVECs.

RESULTS

Secretomes from lung cancer spheroids significantly triggered the endothelial-to-mesenchymal transition (EndMT) process in HUVECs, compared to secretomes from monolayer-cultured lung cancer cells. Interestingly, expression of GSK-3β-targeted genes was altered in MCTSs and inhibition of this activity by a GSK-3β inhibitor induced reversion of EndMT in lung tumor microenvironments. Furthermore, we observed that HUVECs in MCTSs significantly increased the compactness of the spheroids and exhibited strong resistance against Gefitinib and Cisplatin, relative to fibroblasts, by facilitating the EndMT process in HUVECs. Subsequently, EndMT reversion contributed to control of chemoresistance, regardless of the levels of soluble transforming growth factor (TGF)-β. Using the MCTS xenograft mouse model, we demonstrated that inhibition of GSK-3β reduces lung cancer volume, and in combination with Gefitinib, has a synergistic effect on lung cancer therapy.

CONCLUSION

In summary, these findings suggest that targeting EndMT through GSK-3β inhibition in HUVECs might represent a promising therapeutic strategy for lung cancer therapy.

Endothelial to Mesenchymal Transition in Cardiovascular Disease: JACC State-of-the-Art Review

Endothelial to mesenchymal transition (EndMT) is a process whereby an endothelial cell undergoes a series of molecular events that lead to a change in phenotype toward a mesenchymal cell (e.g., myofibroblast, smooth muscle cell). EndMT plays a fundamental role during development, and mounting evidence indicates that EndMT is involved in adult cardiovascular diseases (CVDs), including atherosclerosis, pulmonary hypertension, valvular disease, and fibroelastosis. Therefore, the targeting of EndMT may hold therapeutic promise for treating CVD. However, the field faces a number of challenges, including the lack of a precise functional and molecular definition, a lack of understanding of the causative pathological role of EndMT in CVDs (versus being a "bystander-phenomenon"), and a lack of robust human data corroborating the extent and causality of EndMT in adult CVDs. Here, we review this emerging but exciting field, and propose a framework for its systematic advancement at the molecular and translational levels.

MeCP2 promotes endothelial-to-mesenchymal transition in human endothelial cells by downregulating BMP7 expression

Endothelial-to-mesenchymal transition (EndMT) plays a pivotal role in the development of organ fibrosis and can be induced by TGF-β. It is characterized by the loss of endothelial cell markers and the acquisition of mesenchymal markers. In this study, we found that methyl-CpG binding protein 2 (MeCP2) was increased in TGF-β-induced EndMT, and silencing of MeCP2 inhibited EndMT induction. Viral overexpression of MeCP2 in vitro promoted EndMT and suppressed the expression of bone morphogenic protein-7 (BMP7). The methylation of CpG islands in BMP7 promoter was increased in MeCP2-overexpressing endothelial cells and Chromatin immunoprecipitation assay showed the direct binding of MeCP2 at the BMP7 promoter. In summary, our results suggest that MeCP2 promotes EndMT by epigenetically silencing BMP7 in endothelial cells and MeCP2 may be a target for diseases driven by EndMT.

Fibroblast growth factor-transforming growth factor beta dialogues, endothelial cell to mesenchymal transition, and atherosclerosis

PURPOSE OF REVIEW

Despite much effort, atherosclerosis remains an important public health problem, leading to substantial morbidity and mortality worldwide. The purpose of this review is to provide an understanding of the role of endothelial cell fate change in atherosclerosis process.

RECENT FINDINGS

Recent studies indicate that a process known as endothelial-to-mesenchymal transition (EndMT) may play an important role in atherosclerosis development. Transforming growth factor beta (TGFβ) has been shown to be an important driver of the endothelial cell phenotype transition.

SUMMARY

The current review deals with the current state of knowledge regarding EndMT's role in atherosclerosis and its regulation by fibroblast growth factor (FGF)-TGFβ cross-talk. A better understanding of FGF-TGFβ signaling in the regulation of endothelial cell phenotypes is key to the development of novel therapeutic agents.