Snail is required for TGFbeta-induced endothelial-mesenchymal transition of embryonic stem cell-derived endothelial cells

Functions of the SNAI family in chondrocyte-to-osteocyte development

Different cellular mechanisms contribute to osteocyte development. And while critical roles for members of the zinc finger protein SNAI family (SNAIs) have been discussed in cancer-related models, there are few reviews summarizing their importance for chondrocyte-to-osteocyte development. To help fill this gap, we review the roles of SNAIs in the development of mature osteocytes from chondrocytes, including the regulation of chondro- and osteogenesis through different signaling pathways and in programmed cell death. We also discuss how epigenetic factors-including DNA methylation, histone methylation and acetylation, and noncoding RNAs-contribute differently to both chondrocyte and osteocyte development. To better grasp the important roles of SNAIs in bone development, we also review genotype-phenotype correlations in different animal models. We end with comments about the possible importance of the SNAI family in cartilage/bone development and the potential applications for therapeutic goals.

LncRNA AERRIE Is Required for Sulfatase 1 Expression, but Not for Endothelial-to-Mesenchymal Transition

Endothelial cells can acquire a mesenchymal phenotype through a process called Endothelial-to-Mesenchymal transition (EndMT). This event is found in embryonic development, but also in pathological conditions. Blood vessels lose their ability to maintain vascular homeostasis and ultimately develop atherosclerosis, pulmonary hypertension, or fibrosis. An increase in inflammatory signals causes an upregulation of EndMT transcription factors, mesenchymal markers, and a decrease in endothelial markers. In our study, we show that the induction of EndMT results in an increase in long non-coding RNA AERRIE expression. JMJD2B, a known EndMT regulator, induces AERRIE and subsequently SULF1. Silencing of AERRIE shows a partial regulation of SULF1 but showed no effect on the endothelial and mesenchymal markers. Additionally, the overexpression of AERRIE results in no significant changes in EndMT markers, suggesting that AERRIE is marginally regulating mesenchymal markers and transcription factors. This study identifies AERRIE as a novel factor in EndMT, but its mechanism of action still needs to be elucidated.

Extracellular Superoxide Dismutase (EC-SOD) Regulates Gene Methylation and Cardiac Fibrosis During Chronic Hypoxic Stress

Chronic hypoxic stress induces epigenetic modifications mainly DNA methylation in cardiac fibroblasts, inactivating tumor suppressor genes (RASSF1A) and activating kinases (ERK1/2) leading to fibroblast proliferation and cardiac fibrosis. The Ras/ERK signaling pathway is an intracellular signal transduction critically involved in fibroblast proliferation. RASSF1A functions through its effect on downstream ERK1/2. The antioxidant enzyme, extracellular superoxide dismutase (EC-SOD), decreases oxidative stress from chronic hypoxia, but its effects on these epigenetic changes have not been fully explored. To test our hypothesis, we used an in-vitro model: wild-type C57B6 male mice (WT) and transgenic males with an extra copy of human hEC-SOD (TG). The studied animals were housed in hypoxia (10% O₂) for 21 days. The right ventricular tissue was studied for cardiac fibrosis markers using RT-PCR and Western blot analyses. Primary C57BL6 mouse cardiac fibroblast tissue culture was used to study the in-vitro model, the downstream effects of RASSF-1 expression and methylation, and its relation to ERK1/2. Our findings showed a significant increase in cardiac fibrosis markers: Collagen 1, alpha smooth muscle actin (ASMA), and SNAIL, in the WT hypoxic animals as compared to the TG hypoxic group (p < 0.05). The expression of DNA methylation enzymes (DNMT 1&3b) was significantly increased in the WT hypoxic mice as compared to the hypoxic TG mice (p < 0.001). RASSF1A expression was significantly lower and ERK1/2 was significantly higher in hypoxia WT compared to the hypoxic TG group (p < 0.05). Use of SiRNA to block RASSF1A gene expression in murine cardiac fibroblast tissue culture led to increased fibroblast proliferation (p < 0.05). Methylation of the RASSF1A promoter region was significantly reduced in the TG hypoxic group compared to the WT hypoxic group (0.59 vs. 0.75, respectively). Based on our findings, we can speculate that EC-SOD significantly attenuates RASSF1A gene methylation and can alleviate cardiac fibrosis induced by hypoxia.

Contributions of the Endothelium to Vascular Calcification

Vascular calcification (VC) increases morbidity and mortality and constitutes a significant obstacle during percutaneous interventions and surgeries. On a cellular and molecular level, VC is a highly regulated process that involves abnormal cell transitions and osteogenic differentiation, re-purposing of signaling pathways normally used in bone, and even formation of osteoclast-like cells. Endothelial cells have been shown to contribute to VC through a variety of means. This includes direct contributions of osteoprogenitor cells generated through endothelial-mesenchymal transitions in activated endothelium, with subsequent migration into the vessel wall. The endothelium also secretes pro-osteogenic growth factors, such as bone morphogenetic proteins, inflammatory mediators and cytokines in conditions like hyperlipidemia, diabetes, and renal failure. High phosphate levels caused by renal disease have deleterious effects on the endothelium, and induction of tissue non-specific alkaline phosphatase adds to the calcific process. Furthermore, endothelial activation promotes proteolytic destruction of the internal elastic lamina that serves, among other things, as a stabilizer of the endothelium. Appropriate bone mineralization is highly dependent on active angiogenesis, but it is unclear whether the same relationship exists in VC. Through its location facing the vascular lumen, the endothelium is the first to encounter circulating factor and bone marrow-derived cells that might contribute to osteoclast-like versus osteoblast-like cells in the vascular wall. In the same way, the endothelium may be the easiest target to reach with treatments aimed at limiting calcification. This review provides a brief summary of the contributions of the endothelium to VC as we currently know them.

Sox9 and Rbpj differentially regulate endothelial to mesenchymal transition and wound scarring in murine endovascular progenitors

Endothelial to mesenchymal transition (EndMT) is a leading cause of fibrosis and disease, however its mechanism has yet to be elucidated. The endothelium possesses a profound regenerative capacity to adapt and reorganize that is attributed to a population of vessel-resident endovascular progenitors (EVP) governing an endothelial hierarchy. Here, using fate analysis, we show that two transcription factors SOX9 and RBPJ specifically affect the murine EVP numbers and regulate lineage specification. Conditional knock-out of Sox9 from the vasculature (Sox9^fl/fl/Cdh5-Cre^ERRosaYFP) depletes EVP while enhancing Rbpj expression and canonical Notch signalling. Additionally, skin wound analysis from Sox9 conditional knock-out mice demonstrates a significant reduction in pathological EndMT resulting in reduced scar area. The converse is observed with Rbpj conditionally knocked-out from the murine vasculature (Rbpj^fl/fl/Cdh5-CreER RosaYFP) or inhibition of Notch signaling in human endothelial colony forming cells, resulting in enhanced Sox9 and EndMT related gene (Snail, Slug, Twist1, Twist2, TGF-β) expression. Similarly, increased endothelial hedgehog signaling (Ptch1^fl/fl/Cdh5-CreER RosaYFP), that upregulates the expression of Sox9 in cells undergoing pathological EndMT, also results in excess fibrosis. Endothelial cells transitioning to a mesenchymal fate express increased Sox9, reduced Rbpj and enhanced EndMT. Importantly, using topical administration of siRNA against Sox9 on skin wounds can substantially reduce scar area by blocking pathological EndMT. Overall, here we report distinct fates of EVPs according to the relative expression of Rbpj or Notch signalling and Sox9, highlighting their potential plasticity and opening exciting avenues for more effective therapies in fibrotic diseases.

How endothelial to mesenchymal transition is regulated in endovascular progenitors is unclear. Here, the authors show that blocking Sox9 expression in murine endovascular progenitors regulates this transition on skin wounding, affecting the size of scarring, with changes in Rbpj having the opposite effect.

Drug Resistance in Metastatic Breast Cancer: Tumor Targeted Nanomedicine to the Rescue

Breast cancer, specifically metastatic breast, is a leading cause of morbidity and mortality in women. This is mainly due to relapse and reoccurrence of tumor. The primary reason for cancer relapse is the development of multidrug resistance (MDR) hampering the treatment and prognosis. MDR can occur due to a multitude of molecular events, including increased expression of efflux transporters such as P-gp, BCRP, or MRP1; epithelial to mesenchymal transition; and resistance development in breast cancer stem cells. Excessive dose dumping in chemotherapy can cause intrinsic anti-cancer MDR to appear prior to chemotherapy and after the treatment. Hence, novel targeted nanomedicines encapsulating chemotherapeutics and gene therapy products may assist to overcome cancer drug resistance. Targeted nanomedicines offer innovative strategies to overcome the limitations of conventional chemotherapy while permitting enhanced selectivity to cancer cells. Targeted nanotheranostics permit targeted drug release, precise breast cancer diagnosis, and importantly, the ability to overcome MDR. The article discusses various nanomedicines designed to selectively target breast cancer, triple negative breast cancer, and breast cancer stem cells. In addition, the review discusses recent approaches, including combination nanoparticles (NPs), theranostic NPs, and stimuli sensitive or “smart” NPs. Recent innovations in microRNA NPs and personalized medicine NPs are also discussed. Future perspective research for complex targeted and multi-stage responsive nanomedicines for metastatic breast cancer is discussed.

Endothelium-derived stromal cells contribute to hematopoietic bone marrow niche formation

Bone marrow stromal cells (BMSCs) play pivotal roles in tissue maintenance and regeneration. Their origins, however, remain incompletely understood. Here we identify rare LNGFR⁺ cells in human fetal and regenerative bone marrow that co-express endothelial and stromal markers. This endothelial subpopulation displays transcriptional reprogramming consistent with endothelial-to-mesenchymal transition (EndoMT) and can generate multipotent stromal cells that reconstitute the bone marrow (BM) niche upon transplantation. Single-cell transcriptomics and lineage tracing in mice confirm robust and sustained contributions of EndoMT to bone precursor and hematopoietic niche pools. Interleukin-33 (IL-33) is overexpressed in subsets of EndoMT cells and drives this conversion process through ST2 receptor signaling. These data reveal generation of tissue-forming BMSCs from mouse and human endothelial cells and may be instructive for approaches to human tissue regeneration.

SOX7 suppresses endothelial-to-mesenchymal transitions by enhancing VE-cadherin expression during outflow tract development

The endothelial-to-mesenchymal transition (EndMT) is a critical process that occurs during the development of the outflow tract (OFT). Malformations of the OFT can lead to the occurrence of conotruncal defect (CTD). SOX7 duplication has been reported in patients with congenital CTD, but its specific role in OFT development remains poorly understood. To decipher this, histological analysis showed that SRY-related HMG-box 7 (SOX7) was regionally expressed in the endocardial endothelial cells and in the mesenchymal cells of the OFT, where EndMT occurs. Experiments, using in vitro collagen gel culture system, revealed that SOX7 was a negative regulator of EndMT that inhibited endocardial cell (EC) migration and resulted in decreased number of mesenchymal cells. Forced expression of SOX7 in endothelial cells blocked further migration and improved the expression of the adhesion protein vascular endothelial (VE)-cadherin (VE-cadherin). Moreover, a VE-cadherin knockdown could partly reverse the SOX7-mediated repression of cell migration. Luciferase and electrophoretic mobility shift assay (EMSA) demonstrated that SOX7 up-regulated VE-cadherin by directly binding to the gene's promoter in endothelial cells. The coding exons and splicing regions of the SOX7 gene were also scanned in the 536 sporadic CTD patients and in 300 unaffected controls, which revealed four heterozygous SOX7 mutations. Luciferase assays revealed that two SOX7 variants weakened the transactivation of the VE-cadherin promoter. In conclusion, SOX7 inhibited EndMT during OFT development by directly up-regulating the endothelial-specific adhesion molecule VE-cadherin. SOX7 mutations can lead to impaired EndMT by regulating VE-cadherin, which may give rise to the molecular mechanisms associated with SOX7 in CTD pathogenesis.

Simvastatin inhibits POVPC-mediated induction of endothelial-to-mesenchymal cell transition

Endothelial-to-mesenchymal transition (EndMT), the process by which an endothelial cell (EC) undergoes a series of molecular events that result in a mesenchymal cell phenotype, plays an important role in atherosclerosis. 1-Palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC), derived from the oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphatidylcholine, is a proinflammatory lipid found in atherosclerotic lesions. Whether POVPC promotes EndMT and how simvastatin influences POVPC-mediated EndMT remains unclear. Here, we treated human umbilical vein ECs with POVPC, simvastatin, or both, and determined their effect on EC viability, morphology, tube formation, proliferation, and generation of NO and superoxide anion (O2•-). Expression of specific endothelial and mesenchymal markers was detected by immunofluorescence and immunoblotting. POVPC did not affect EC viability but altered cellular morphology from cobblestone-like ECs to a spindle-like mesenchymal cell morphology. POVPC increased O2- generation and expression of alpha-smooth muscle actin, vimentin, Snail-1, Twist-1, transforming growth factor-beta (TGF-β), TGF-β receptor II, p-Smad2/3, and Smad2/3. POVPC also decreased NO production and expression of CD31 and endothelial NO synthase. Simvastatin inhibited POVPC-mediated effects on cellular morphology, production of O2•- and NO, and expression of specific endothelial and mesenchymal markers. These data demonstrate that POVPC induces EndMT by increasing oxidative stress, which stimulates TGF-β/Smad signaling, leading to Snail-1 and Twist-1 activation. Simvastatin inhibited POVPC-induced EndMT by decreasing oxidative stress, suppressing TGF-β/Smad signaling, and inactivating Snail-1 and Twist-1. Our findings reveal a novel mechanism of atherosclerosis that can be inhibited by simvastatin.

TGF-β-Induced Endothelial to Mesenchymal Transition Is Determined by a Balance Between SNAIL and ID Factors

Endothelial-to-mesenchymal transition (EndMT) plays an important role in embryonic development and disease progression. Yet, how different members of the transforming growth factor-β (TGF-β) family regulate EndMT is not well understood. In the current study, we report that TGF-β2, but not bone morphogenetic protein (BMP)9, triggers EndMT in murine endothelial MS-1 and 2H11 cells. TGF-β2 strongly upregulates the transcription factor SNAIL, and the depletion of Snail is sufficient to abrogate TGF-β2-triggered mesenchymal-like cell morphology acquisition and EndMT-related molecular changes. Although SLUG is not regulated by TGF-β2, knocking out Slug also partly inhibits TGF-β2-induced EndMT in 2H11 cells. Interestingly, in addition to SNAIL and SLUG, BMP9 stimulates inhibitor of DNA binding (ID) proteins. The suppression of Id1, Id2, or Id3 expression facilitated BMP9 in inducing EndMT and, in contrast, ectopic expression of ID1, ID2, or ID3 abrogated TGF-β2-mediated EndMT. Altogether, our results show that SNAIL is critical and indispensable for TGF-β2-mediated EndMT. Although SLUG is also involved in the EndMT process, it plays less of a crucial role in it. In contrast, ID proteins are essential for maintaining endothelial traits and repressing the function of SNAIL and SLUG during the EndMT process. These data suggest that the control over endothelial vs. mesenchymal cell states is determined, at least in part, by a balance between the expression of SNAIL/SLUG and ID proteins.

Clinicopathologic Correlations of Retrocorneal Membranes Associated With Endothelial Corneal Graft Failure

PURPOSE

To provide clinicopathologic correlations for retrocorneal membranes associated with Descemet stripping automated endothelial keratoplasty (DSAEK) failure.

DESIGN

Retrospective case series.

METHODS

The specimens and medical records of the patients diagnosed with clinically significant retrocorneal membranes associated with DSAEK failure at the Bascom Palmer Eye Institute or the University of Miami Veterans Hospital between October 2015 and March 2020 were reviewed for demographics, clinical presentation, comorbidities, and surgeries performed. Histopathologic analysis was performed on hematoxylin-eosin and periodic acid-Schiff sections. Immunohistochemical studies were performed for smooth muscle actin (α-SMA), pancytokeratin, and CK7. Immunofluorescence was performed for vimentin, N-cadherin, ROCK1, RhoA, ZEB1, and Snail.

RESULTS

A total of 7 patients (3 male and 4 female) were identified to have a clinically significant retrocorneal membranes at the time of graft failure. The average age at the time of first DSAEK was 70 years (range: 55-85 years). All patients were pseudophakic and had a glaucoma drainage device in place; 1 had a history of failed DSAEK. Ranging from 0 to 47 months after surgery, a variably thick retrocorneal fibrous membrane was observed, eventually leading to graft failure. Four patients underwent subsequent penetrating keratoplasty and 3 underwent repeat DSAEK. On histopathologic evaluation, a pigmented fibrocellular tissue was identified along the posterior margin of the corneas and DSAEK buttons in all cases. Further characterization with immunohistochemistry and immunofluorescence demonstrated membranes to be negative for pancytokeratin and positive for α-SMA, vimentin, CK7, N-cadherin, ZEB1, Snail, ROCK1, and RhoA.

CONCLUSIONS

Fibrocellular retrocorneal membrane proliferation may be associated with DSAEK failure in patients with previous glaucoma drainage device surgery. Our results demonstrate myofibroblastic differentiation and a lack of epithelial differentiation. Positivity for markers of an endothelial-to-mesenchymal transition indicates possible endothelial origin and could be the hallmark for future targeted pharmacotherapy.

Pyrogallol-Phloroglucinol-6 6-Bieckol on Attenuates High-Fat Diet-Induced Hypertension by Modulating Endothelial-to-Mesenchymal Transition in the Aorta of Mice

Endothelial-to-mesenchymal transition (EndMT), which is involved in the development of various cardiovascular diseases, is induced by dyslipidemia or obesity. In dyslipidemia, the increased levels of oxidized low-density lipoproteins (oxLDL) upregulated the lectin-type oxidized LDL receptor 1 (Lox-1), which then upregulated the down signaling pathways of PKC-α/MMPs/TGF-β/SMAD2 or 3 and increased the EndMT. In this study, we investigated the effect of pyrogallol-phloroglucinol-6,6-bieckol (PPB), which is a compound of Ecklonia cava (E. cava), on decreased blood pressure (BP) by attenuating the EndMT in a high-fat diet- (HFD-) fed animal model. We also investigated PPB's attenuation effect on EndMT in oxLDL-treated mouse endothelial cells as an in vitro model. The results indicated that, in the aorta or endothelial cells of mice, the HFD or oxLDL treatment significantly increased the expression of Lox-1/PKC-α/MMP9/TGF-β/SMAD2/SMAD3. The PPB treatment significantly decreased its expression. In contrast, the HFD or oxLDL treatment significantly decreased the expression of the EC markers (PECAM-1 and vWF) while the PPB treatment significantly increased them. Moreover, the HFD or oxLDL treatment significantly increased the expression of the mesenchymal cell markers (α-SMA and vimentin) while PPB treatment significantly decreased them. PPB decreased the intima-media thickness and extracellular matrix amount of the aorta and attenuated the BP, which was increased by the HFD. In conclusion, PPB attenuated the upregulation of Lox-1/PKC-α/MMP9/TGF-β/SMAD2 and 3 and restored the EndMT in HFD-fed animals. Moreover, PPB showed a restoring effect on HFD-induced hypertension.

TGF-β in Cancer: Metabolic Driver of the Tolerogenic Crosstalk in the Tumor Microenvironment

Overcoming tumor immunosuppression still represents one ambitious achievement for cancer immunotherapy. Of note, the cytokine TGF-β contributes to immune evasion in multiple cancer types, by feeding the establishment of a tolerogenic environment in the host. Indeed, it fosters the expansion and accumulation of immunosuppressive regulatory cell populations within the tumor microenvironment (TME), where it also activates resident stromal cells and enhances angiogenesis programs. More recently, TGF-β has also turned out as a key metabolic adjuster in tumors orchestrating metabolic pathways in the TME. In this review, we will scrutinize TGF-β-mediated immune and stromal cell crosstalk within the TME, with a primary focus on metabolic programs.

Protective Effects of Eicosapentaenoic Acid on the Glomerular Endothelium via Inhibition of EndMT in Diabetes

Diabetes-induced endothelial pathologies are hypothesized to lead to the progression of diabetic kidney disease (DKD). The endothelial to mesenchymal transition (EndMT) possibly induces fibrosis, leading to glomerulosclerosis in the kidney. Furthermore, this could lead to albuminuria in diabetic nephropathy due to glomerular endothelial dysfunction. Eicosapentaenoic acid (EPA), purified from fish oil, decreases inflammatory cytokine levels in glomerulonephritis. Here, we aimed at finding whether ethyl eicosapentaenoate (EPA-E) exerts renal protective effects via EndMT inhibition. To find out whether EPA inhibits EndMT in vitro, the changes in CD31 expression were studied in cultured mouse endothelial cells. The addition of the conditioned medium from the adipocyte culture significantly decreased the protein levels of CD31, while the addition of EPA-E partially reversed this inhibition. Further, EndMT inhibition by EPA-E treatment might occur via the inhibition of the protein kinase Cβ (PKCβ)/transforming growth factor-β (TGF-β)/plasminogen activator inhibitor-1 (PAI-1) signaling and not via microRNAs. Streptozotocin-induced diabetic mice fed a high-fat diet (60% from fat) exhibited mesangial expansion and albuminuria. Induction of EPA-E ameliorated the mesangial expansion and decreased albuminuria without affecting blood pressure, triglyceride and free fatty acid levels, and intraperitoneal glucose. These findings suggest that EPA-E exerts renal protective effects on endothelial cells, by normalizing EndMT followed by the PKCβ/TGF-β/PAI-1 signaling. Thus, EPA-E has the potential for imparting renal protection by regulating EndMT in DKD.

Diverse origins and activation of fibroblasts in cardiac fibrosis

Cardiac fibroblasts (cFBs) have emerged as a heterogenous cell population. Fibroblasts are considered the main cell source for synthesis of the extracellular matrix (ECM) and as such a dysregulation in cFB function, activity, or viability can lead to disrupted ECM structure or fibrosis. Fibrosis can be initiated in response to different injuries and stimuli, and can be reparative (beneficial) or reactive (damaging). FBs need to be activated to myofibroblasts (MyoFBs) which have augmented capacity in synthesizing ECM proteins, causing fibrosis. In addition to the resident FBs in the myocardium, a number of other cells (pericytes, fibrocytes, mesenchymal, and hematopoietic cells) can transform into MyoFBs, further driving the fibrotic response. Multiple molecules including hormones, cytokines, and growth factors stimulate this process leading to generation of activated MyoFBs. Contribution of different cell types to cFBs and MyoFBs can result in an exponential increase in the number of MyoFBs and an accelerated pro-fibrotic response. Given the diversity of the cell sources, and the array of interconnected signalling pathways that lead to formation of MyoFBs and subsequently fibrosis, identifying a single target to limit the fibrotic response in the myocardium has been challenging. This review article will delineate the importance and relevance of fibroblast heterogeneity in mediating fibrosis in different models of heart failure and will highlight important signalling pathways implicated in myofibroblast activation.

Vascular calcification: New insights into endothelial cells

Vascular calcification, a common pathological basis of vascular disease, is caused by various diseases and is an independent risk factor for cardiovascular events. Therefore, elucidating the pathogenesis of vascular calcification has significant clinical benefits. It is generally believed that vascular calcification is similar to the processes of bone development and cartilage formation. The transformation of vascular smooth muscle cells into osteoblast- and chondrocyte-like cells is a key event. However, recent studies have found that under certain conditions, endothelial cells participate in vascular calcification via endothelial-mesenchymal transition, cytokine secretion, extracellular vesicle synthesis, angiogenesis regulation and hemodynamics. This review aims to explore the relationship between endothelial cells and vascular calcification and to provide a theoretical basis and new ideas for the active prevention and treatment of vascular calcification in the clinic.

The landscape of long non-coding RNAs in tumor stroma

AIMS

Long non-coding RNAs (lncRNAs) are associated with cancer development, while their relationship with the cancer-associated stromal components remains poorly understood. In this review, we performed a broad description of the functional landscape of stroma-associated lncRNAs in various cancers and their roles in regulating the tumor-stroma crosstalk.

MATERIALS AND METHODS

We carried out a systematic literature review of PubMed, Scopus, Medline, Bentham, and EMBASE (Elsevier) databases by using the keywords "LncRNAs in cancer," "LncRNAs in tumor stroma," "stroma," "cancer-associated stroma," "stroma in the tumor microenvironment," "tumor-stroma crosstalk," "drug resistance of stroma," and "stroma in immunosuppression" till July 2020. We collected the latest articles addressing the biological functions of stroma-associated lncRNAs in cancer.

KEY FINDINGS

These articles reported that dysregulated stroma-associated lncRNAs play significant roles in modulating the tumor microenvironment (TME) by the regulation of tumor-stroma crosstalk, epithelial to mesenchymal transition (EMT), endothelial to mesenchymal transition (EndMT), extracellular matrix (ECM) turnover, and tumor immunity.

SIGNIFICANCE

The tumor stroma is a substantial portion of the TME, and the dysregulation of tumor stroma-associated lncRNAs significantly contributes to cancer initiation, progression, angiogenesis, immune evasion, metastasis, and drug resistance. Thus, stroma-associated lncRNAs could be potentially useful targets for cancer therapy.

New Concepts in the Development and Malformation of the Arterial Valves

Although in many ways the arterial and atrioventricular valves are similar, both being derived for the most part from endocardial cushions, we now know that the arterial valves and their surrounding structures are uniquely dependent on progenitors from both the second heart field (SHF) and neural crest cells (NCC). Here, we will review aspects of arterial valve development, highlighting how our appreciation of NCC and the discovery of the SHF have altered our developmental models. We will highlight areas of research that have been particularly instructive for understanding how the leaflets form and remodel, as well as those with limited or conflicting results. With this background, we will explore how this developmental knowledge can help us to understand human valve malformations, particularly those of the bicuspid aortic valve (BAV). Controversies and the current state of valve genomics will be indicated.

Endothelial-to-Mesenchymal Transition: Role in Cardiac Fibrosis

Endothelial-to-mesenchymal transition (EndMT) is a complex biological process by which endothelial cells lose their endothelial cell characteristics and acquire mesenchymal cell properties under certain physiological or pathological conditions. Recently, it has been found that EndMT plays an important role in the occurrence and development of fibrotic cardiovascular diseases. In this review, we first summarize the main induction pathways involved in EndMT process. In addition, we discuss the role of EndMT in fibrotic cardiovascular diseases and its potential implication in new therapeutic interventions.

It Takes Two to Tango: Endothelial TGFβ/BMP Signaling Crosstalk with Mechanobiology

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta (TGFβ) superfamily of cytokines. While some ligand members are potent inducers of angiogenesis, others promote vascular homeostasis. However, the precise understanding of the molecular mechanisms underlying these functions is still a growing research field. In bone, the tissue in which BMPs were first discovered, crosstalk of TGFβ/BMP signaling with mechanobiology is well understood. Likewise, the endothelium represents a tissue that is constantly exposed to multiple mechanical triggers, such as wall shear stress, elicited by blood flow or strain, and tension from the surrounding cells and to the extracellular matrix. To integrate mechanical stimuli, the cytoskeleton plays a pivotal role in the transduction of these forces in endothelial cells. Importantly, mechanical forces integrate on several levels of the TGFβ/BMP pathway, such as receptors and SMADs, but also global cell-architecture and nuclear chromatin re-organization. Here, we summarize the current literature on crosstalk mechanisms between biochemical cues elicited by TGFβ/BMP growth factors and mechanical cues, as shear stress or matrix stiffness that collectively orchestrate endothelial function. We focus on the different subcellular compartments in which the forces are sensed and integrated into the TGFβ/BMP growth factor signaling.

Endothelial-to-Mesenchymal Transition and Inflammation Play Key Roles in Cyclophilin A-Induced Pulmonary Arterial Hypertension

Oxidative stress and inflammation play key roles in development of pulmonary arterial hypertension (PAH). We previously reported that an endothelial cell (EC)-specific cyclophilin A overexpression mouse developed many characteristics of PAH. In other models of cardiovascular disease, cyclophilin A stimulates smooth muscle proliferation and vascular inflammation, but mechanisms responsible for PAH have not been defined. In particular, the contribution of endothelial-to-mesenchymal transition in cyclophilin A-mediated PAH has not been studied. We identified increased levels of cyclophilin A in endothelial and neointimal cells of pulmonary arteries in patients with PAH and animal pulmonary hypertension models. In the EC-specific cyclophilin A overexpression mouse that exhibited features characteristic of PAH, lineage tracing showed high level expression of mesenchymal markers in pulmonary ECs. A significant number of mesenchymal cells in media and perivascular regions of pulmonary arterioles and alveoli were derived from ECs. Pulmonary ECs isolated from these mice showed phenotypic changes characteristic of endothelial-to-mesenchymal transition in culture. Cultured pulmonary ECs stimulated with extracellular cyclophilin A and acetylated cyclophilin A demonstrated functional changes associated with endothelial-to-mesenchymal transition such as increased cytokine release, migration, proliferation, and mitochondrial dysfunction. Acetylated cyclophilin A stimulated greater increases for most features of endothelial-to-mesenchymal transition. In conclusion, extracellular cyclophilin A (especially acetylated form) contributes to PAH by mechanisms involving increased endothelial-to-mesenchymal transition, cytokine release, EC migration, proliferation, and mitochondrial dysfunction; strengthening the basis for studying cyclophilin A inhibition as a therapy for PAH.

The New Model of Snail Expression Regulation: The Role of MRTFs in Fast and Slow Endothelial-Mesenchymal Transition

Endothelial–mesenchymal transition (EndMT) is a crucial phenomenon in regulating the development of diseases, including cancer metastasis and fibrotic disorders. The primary regulators of disease development are zinc-finger transcription factors belonging to the Snail family. In this study, we characterized the myocardin-related transcription factor (MRTF)-dependent mechanisms of a human snail promoter regulation in TGF-β-stimulated human endothelial cells. Although in silico analysis revealed that the snail promoter’s regulatory fragment contains one GCCG and two SP1 motifs that could be occupied by MRTFs, the genetic study confirmed that MRTF binds only to SP1 sites to promote snail expression. The more accurate studies revealed that MRTF-A binds to both SP1 elements, whereas MRTF-B to only one (SP1near). Although we found that each MRTF alone is capable of inducing snail expression, the direct cooperation of these proteins is required to reinforce snail expression and promote the late stages of EndMT within 48 hours. Furthermore, genetic and biochemical analysis revealed that MRTF-B alone could induce the late stage of EndMT. However, it requires a prolonged time. Therefore, we concluded that MRTFs might cause EndMT in a fast- and slow-dependent manner. Based on MRTF-dependent Snail upregulation, we recognized that TGF-β1, as an MRTF-B regulator, is involved in slow EndMT induction, whereas TGF-β2, which altered both MRTF-A and MRTF-B expression, promotes a fast EndMT process.

Endothelial-to-Mesenchymal Transition in Cancer

Cancer is one of the most important causes of morbidity and mortality worldwide. Tumor cells grow in a complex microenvironment constituted of immune, stromal, and vascular cells that supports growth, angiogenesis, and metastasis. Endothelial cells (ECs) are major components of the vascular microenvironment. These cells have been described for their plasticity and potential to transdifferentiate into mesenchymal cells through a process known as endothelial-to-mesenchymal transition (EndMT). This complex process is controlled by various factors, by which ECs convert into a phenotype characterized by mesenchymal protein expression and motile, contractile morphology. Initially described in normal heart development, EndMT is now identified in several pathologies, and especially in cancer. In this review, we highlight the process of EndMT in the context of cancer and we discuss it as an important adaptive process of the tumor microenvironment that favors tumor growth and dissemination but also resistance to treatment. Thus, we underline targeting of EndMT as a potential therapeutic strategy.

Dual roles of chromatin remodeling protein BRG1 in angiotensin II-induced endothelial-mesenchymal transition

Endothelial–mesenchymal transition (EndMT) is considered one of the processes underlying tissue fibrosis by contributing to the pool of myofibroblasts. In the present study, we investigated the epigenetic mechanism whereby angiotensin II (Ang II) regulates EndMT to promote cardiac fibrosis focusing on the role of chromatin remodeling protein BRG1. BRG1 knockdown or inhibition attenuated Ang II-induced EndMT, as evidenced by down-regulation of CDH5, an endothelial marker, and up-regulation of COL1A2, a mesenchymal marker, in cultured vascular endothelial cells. On the one hand, BRG1 interacted with and was recruited by Sp1 to the SNAI2 (encoding SLUG) promoter to activate SNAI2 transcription in response to Ang II stimulation. Once activated, SLUG bound to the CDH5 promoter to repress CDH5 transcription. On the other hand, BRG1 interacted with and was recruited by SRF to the COL1A2 promoter to activate COL1A2 transcription. Mechanistically, BRG1 evicted histones from the target promoters to facilitate the bindings of Sp1 and SRF. Finally, endothelial conditional BRG1 knockout mice (CKO) exhibited a reduction in cardiac fibrosis, compared to the wild type (WT) littermates, in response to chronic Ang II infusion. In conclusion, our data demonstrate that BRG1 is a key transcriptional coordinator programming Ang II-induced EndMT to contribute to cardiac fibrosis.

TNF-α enhances TGF-β-induced endothelial-to-mesenchymal transition via TGF-β signal augmentation

The tumor microenvironment (TME) consists of various components including cancer cells, tumor vessels, cancer-associated fibroblasts (CAFs), and inflammatory cells. These components interact with each other via various cytokines, which often induce tumor progression. Thus, a greater understanding of TME networks is crucial for the development of novel cancer therapies. Many cancer types express high levels of TGF-β, which induces endothelial-to-mesenchymal transition (EndMT), leading to formation of CAFs. Although we previously reported that CAFs derived from EndMT promoted tumor formation, the molecular mechanisms underlying these interactions remain to be elucidated. Furthermore, tumor-infiltrating inflammatory cells secrete various cytokines, including TNF-α. However, the role of TNF-α in TGF-β-induced EndMT has not been fully elucidated. Therefore, this study examined the effect of TNF-α on TGF-β-induced EndMT in human endothelial cells (ECs). Various types of human ECs underwent EndMT in response to TGF-β and TNF-α, which was accompanied by increased and decreased expression of mesenchymal cell and EC markers, respectively. In addition, treatment of ECs with TGF-β and TNF-α exhibited sustained activation of Smad2/3 signals, which was presumably induced by elevated expression of TGF-β type I receptor, TGF-β2, activin A, and integrin αv, suggesting that TNF-α enhanced TGF-β-induced EndMT by augmenting TGF-β family signals. Furthermore, oral squamous cell carcinoma-derived cells underwent epithelial-to-mesenchymal transition (EMT) in response to humoral factors produced by TGF-β and TNF-α-cultured ECs. This EndMT-driven EMT was blocked by inhibiting the action of TGF-βs. Collectively, our findings suggest that TNF-α enhances TGF-β-dependent EndMT, which contributes to tumor progression.

Blocking protein phosphatase 2A with a peptide protects mice against bleomycin-induced pulmonary fibrosis

Emerging data indicate that endothelial-mesenchymal transition (EndMT) is involved in the pathogenesis of idiopathic pulmonary fibrosis (IPF). A previous study noted that blocking the activity of protein phosphatase 2 A (PP2A) could attenuate EndMT. However, the treatment effects of PP2A inhibitors in pulmonary fibrosis remain not investigated. In the present study, we used a PP2A inhibitor, a newly designed peptide named TAT-Y127WT, to determine the role of PP2A in pulmonary fibrosis. Herein, we showed that TAT-Y127WT protected mice against BLM-induced pulmonary fibrosis by attenuating lung injury and fibrosis. Furthermore, a mechanistic study indicated that TAT-Y127WT could alleviate EndMT in the lungs following BLM induction. Overall, our data showed that PP2A might participate in pulmonary fibrogenesis by promoting EndMT, and TAT-Y127WT could be a potential candidate for new anti-fibrotic therapies for IPF patients.

Positive Feedback Loop of SNAIL-IL-6 Mediates Myofibroblastic Differentiation Activity in Precancerous Oral Submucous Fibrosis

Oral submucosal fibrosis (OSF) is a premalignant disorder of the oral cavity, and areca nut chewing is known to be a major etiological factor that could induce epithelial to mesenchymal transition (EMT) and activate buccal mucosal fibroblasts (BMFs). However, this detailed mechanism is not fully understood. In this study, we showed that the upregulation of Snail in OSF samples and fibrotic BMFs (fBMFs) may result from constant irritation by arecoline, a major alkaloid of the areca nut. The elevation of Snail triggered myofibroblast transdifferentiation and was crucial to the persistent activation of fBMFs. Meanwhile, Snail increased the expression of numerous fibrosis factors (e.g., α-SMA and collagen I) as well as IL-6. Results from bioinformatics software and a luciferase-based reporter assay revealed that IL-6 was a direct target of Snail. Moreover, IL-6 in BMFs was found to further increase the expression of Snail and mediate Snail-induced myofibroblast activation. These findings suggested that there was a positive loop between Snail and IL-6 to regulate the areca nut-associated myofibroblast transdifferentiation, which implied that the blockage of Snail may serve as a favorable therapeutic strategy for OSF treatment.

EMT and EndMT: Emerging Roles in Age-Related Macular Degeneration

Epithelial–mesenchymal transition (EMT) and endothelial–mesenchymal transition (EndMT) are physiological processes required for normal embryogenesis. However, these processes can be hijacked in pathological conditions to facilitate tissue fibrosis and cancer metastasis. In the eye, EMT and EndMT play key roles in the pathogenesis of subretinal fibrosis, the end-stage of age-related macular degeneration (AMD) that leads to profound and permanent vision loss. Predominant in subretinal fibrotic lesions are matrix-producing mesenchymal cells believed to originate from the retinal pigment epithelium (RPE) and/or choroidal endothelial cells (CECs) through EMT and EndMT, respectively. Recent evidence suggests that EMT of RPE may also be implicated during the early stages of AMD. Transforming growth factor-beta (TGFβ) is a key cytokine orchestrating both EMT and EndMT. Investigations in the molecular mechanisms underpinning EMT and EndMT in AMD have implicated a myriad of contributing factors including signaling pathways, extracellular matrix remodelling, oxidative stress, inflammation, autophagy, metabolism and mitochondrial dysfunction. Questions arise as to differences in the mesenchymal cells derived from these two processes and their distinct mechanistic contributions to the pathogenesis of AMD. Detailed discussion on the AMD microenvironment highlights the synergistic interactions between RPE and CECs that may augment the EMT and EndMT processes in vivo. Understanding the differential regulatory networks of EMT and EndMT and their contributions to both the dry and wet forms of AMD can aid the development of therapeutic strategies targeting both RPE and CECs to potentially reverse the aberrant cellular transdifferentiation processes, regenerate the retina and thus restore vision.

Endothelial-to-mesenchymal transition compromises vascular integrity to induce Myc-mediated metabolic reprogramming in kidney fibrosis

Endothelial-to-mesenchymal transition (EndMT) is a cellular transdifferentiation program in which endothelial cells partially lose their endothelial identity and acquire mesenchymal-like features. Renal capillary endothelial cells can undergo EndMT in association with persistent damage of the renal parenchyma. The functional consequence(s) of EndMT in kidney fibrosis remains unexplored. Here, we studied the effect of Twist or Snail deficiency in endothelial cells on EndMT in kidney fibrosis. Conditional deletion of Twist1 (which encodes Twist) or Snai1 (which encodes Snail) in VE-cadherin⁺ or Tie1⁺ endothelial cells inhibited the emergence of EndMT and improved kidney fibrosis in two different kidney injury/fibrosis mouse models. Suppression of EndMT limited peritubular vascular leakage, reduced tissue hypoxia, and preserved tubular epithelial health and function. Hypoxia, which was exacerbated by EndMT, resulted in increased Myc abundance in tubular epithelial cells, enhanced glycolysis, and suppression of fatty acid oxidation. Pharmacological suppression or epithelial-specific genetic ablation of Myc in tubular epithelial cells ameliorated fibrosis and restored renal parenchymal function and metabolic homeostasis. Together, these findings demonstrate a functional role for EndMT in the response to kidney capillary endothelial injury and highlight the contribution of endothelial-epithelial cross-talk in the development of kidney fibrosis with a potential for therapeutic intervention.

TGF-beta and TNF-alpha cooperatively induce mesenchymal transition of lymphatic endothelial cells via activation of Activin signals

Lymphatic systems play important roles in the maintenance of fluid homeostasis and undergo anatomical and physiological changes during inflammation and aging. While lymphatic endothelial cells (LECs) undergo mesenchymal transition in response to transforming growth factor-β (TGF-β), the molecular mechanisms underlying endothelial-to-mesenchymal transition (EndMT) of LECs remain largely unknown. In this study, we examined the effect of TGF-β2 and tumor necrosis factor-α (TNF-α), an inflammatory cytokine, on EndMT using human skin-derived lymphatic endothelial cells (HDLECs). TGF-β2-treated HDLECs showed increased expression of SM22α, a mesenchymal cell marker accompanied by increased cell motility and vascular permeability, suggesting HDLECs to undergo EndMT. Our data also revealed that TNF-α could enhance TGF-β2-induced EndMT of HDLECs. Furthermore, both cytokines induced the production of Activin A while decreasing the expression of its inhibitory molecule Follistatin, and thus enhancing EndMT. Finally, we demonstrated that human dermal lymphatic vessels underwent EndMT during aging, characterized by double immunostaining for LYVE1 and SM22α. These results suggest that both TGF-β and TNF-α signals play a central role in EndMT of LECs and could be potential targets for senile edema.

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.

Transforming Growth Factor-Beta1 in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) worldwide. Renin-angiotensin-aldosterone system (RAAS) inhibitors and sodium-glucose co-transporter 2 (SGLT2) inhibitors have shown efficacy in reducing the risk of ESRD. However, patients vary in their response to RAAS blockades, and the pharmacodynamic responses to SGLT2 inhibitors decline with increasing severity of renal impairment. Thus, effective therapy for DKD is yet unmet. Transforming growth factor-β1 (TGF-β1), expressed by nearly all kidney cell types and infiltrating leukocytes and macrophages, is a pleiotropic cytokine involved in angiogenesis, immunomodulation, and extracellular matrix (ECM) formation. An overactive TGF-β1 signaling pathway has been implicated as a critical profibrotic factor in the progression of chronic kidney disease in human DKD. In animal studies, TGF-β1 neutralizing antibodies and TGF-β1 signaling inhibitors were effective in ameliorating renal fibrosis in DKD. Conversely, a clinical study of TGF-β1 neutralizing antibodies failed to demonstrate renal efficacy in DKD. However, overexpression of latent TGF-β1 led to anti-inflammatory and anti-fibrosis effects in non-DKD. This evidence implied that complete blocking of TGF-β1 signaling abolished its multiple physiological functions, which are highly associated with undesirable adverse events. Ideal strategies for DKD therapy would be either specific and selective inhibition of the profibrotic-related TGF-β1 pathway or blocking conversion of latent TGF-β1 to active TGF-β1.

Rupatadine, a dual antagonist of histamine and platelet-activating factor (PAF), attenuates experimentally induced diabetic nephropathy in rats

The role of histamine and platelet activating factor (PAF) as involved mediators in the pathophysiology of diabetic complications, in particular diabetic nephropathy (DN), has become a new focus of concern. Accordingly, the present study designed to explore the effect of rupatadine (RUP), a dual antagonist of histamine (H1) and PAF, on the progression of experimentally induced DN in rats. Rats were divided into five groups: control, RUP alone, streptozotocin (STZ)-diabetic model, STZ/RUP (3 mg/kg/day), and STZ/RUP (6 mg/kg/day). Treatment has continued for 4 weeks after diabetes confirmation. At the end of the study, serum was collected for measurement of glucose, insulin, urea, creatinine, histamine, and PAF. Renal tissue homogenates were prepared for measuring oxidative stress indices, tumor necrosis factor (TNF-α), cystatin C, and p21. Moreover, immunohistochemical expression of transforming growth factor-β1 (TGF-β1) and p53 along with histological pictures was also conducted. Antagonizing H1 and PAF receptors by RUP ameliorated the experimentally induced DN as evident by decreasing all serum parameters augmented by STZ together with improvement of the histopathological picture. RUP administration also improved oxidative-antioxidative agents with reduction in the anti-inflammatory marker, TNF-α. Additionally, the immunohistochemical expression of the fibrosis marker; TGF-β1, was also decreased. STZ-induced DN showed a p21/p53-dependent induction of premature senescence and RUP administration decreased the expression of p21 and p53 levels in injured renal tissue. RUP represents a novel promising drug to prevent DN complicated diabetes probably via its inhibitory effect on H1 and PAF receptors. The renal protection was also related to the anti-inflammatory and antioxidant roles and PAF-facilitated senescence effect via p21/p53 signaling.

A Computational Model of the Endothelial to Mesenchymal Transition

Endothelial cells (ECs) form the lining of lymph and blood vessels. Changes in tissue requirements or wounds may cause ECs to behave as tip or stalk cells. Alternatively, they may differentiate into mesenchymal cells (MCs). These processes are known as EC activation and endothelial-to-mesenchymal transition (EndMT), respectively. EndMT, Tip, and Stalk EC behaviors all require SNAI1, SNAI2, and Matrix metallopeptidase (MMP) function. However, only EndMT inhibits the expression of VE-cadherin, PECAM1, and VEGFR2, and also leads to EC detachment. Physiologically, EndMT is involved in heart valve development, while a defective EndMT regulation is involved in the physiopathology of cardiovascular malformations, congenital heart disease, systemic and organ fibrosis, pulmonary arterial hypertension, and atherosclerosis. Therefore, the control of EndMT has many promising potential applications in regenerative medicine. Despite the fact that many molecular components involved in EC activation and EndMT have been characterized, the system-level molecular mechanisms involved in this process have not been elucidated. Toward this end, hereby we present Boolean network model of the molecular involved in the regulation of EC activation and EndMT. The simulated dynamic behavior of our model reaches fixed and cyclic patterns of activation that correspond to the expected EC and MC cell types and behaviors, recovering most of the specific effects of simple gain and loss-of-function mutations as well as the conditions associated with the progression of several diseases. Therefore, our model constitutes a theoretical framework that can be used to generate hypotheses and guide experimental inquiry to comprehend the regulatory mechanisms behind EndMT. Our main findings include that both the extracellular microevironment and the pattern of molecular activity within the cell regulate EndMT. EndMT requires a lack of VEGFA and sufficient oxygen in the extracellular microenvironment as well as no FLI1 and GATA2 activity within the cell. Additionally Tip cells cannot undergo EndMT directly. Furthermore, the specific conditions that are sufficient to trigger EndMT depend on the specific pattern of molecular activation within the cell.

Activated FGF2 signaling pathway in tumor vasculature is essential for acquired resistance to anti-VEGF therapy

Anti-vascular endothelial growth factor (VEGF) therapy shows antitumor activity against various types of solid cancers. Several resistance mechanisms against anti-VEGF therapy have been elucidated; however, little is known about the mechanisms by which the acquired resistance arises. Here, we developed new anti-VEGF therapy-resistant models driven by chronic expression of the mouse VEGFR2 extracellular domain fused with the human IgG4 fragment crystallizable (Fc) region (VEGFR2-Fc). In the VEGFR2-Fc-expressing resistant tumors, we demonstrated that the FGFR2 signaling pathway was activated, and pericytes expressing high levels of FGF2 were co-localized with endothelial cells. Lenvatinib, a multiple tyrosine kinase inhibitor including VEGFR and FGFR inhibition, showed marked antitumor activity against VEGFR2-Fc-expressing resistant tumors accompanied with a decrease in the area of tumor vessels and suppression of phospho-FGFR2 in tumors. Our findings reveal the key role that intercellular FGF2 signaling between pericytes and endothelial cells plays in maintaining the tumor vasculature in anti-VEGF therapy-resistant tumors.

Clonally selected primitive endothelial cells promote occlusive pulmonary arteriopathy and severe pulmonary hypertension in rats exposed to chronic hypoxia

One current concept suggests that unchecked proliferation of clonally selected precursors of endothelial cells (ECs) contribute to severe pulmonary arterial hypertension (PAH). We hypothesized that clonally selected ECs expressing the progenitor marker CD117 promote severe occlusive pulmonary hypertension (PH). The remodelled pulmonary arteries of PAH patients harboured CD117⁺ ECs. Rat lung CD117⁺ ECs underwent four generations of clonal expansion to enrich hyperproliferative ECs. The resulting clonally enriched ECs behaved like ECs, as measured by in vitro and in vivo angiogenesis assays. The same primitive ECs showed a limited ability for mesenchymal lineage differentiation. Endothelial differentiation and function were enhanced by blocking TGF-β signalling, promoting bone morphogenic protein (BMP) signalling. The transplantation of the EC clones caused arterio-occlusive PH in rats exposed to chronic hypoxia. These EC clones engrafted in the pulmonary arteries. Yet cessation of chronic hypoxia promoted lung cell apoptosis and resolution of vascular lesions. In conclusion, this is to the best of our knowledge, the first report that clonally enriched primitive ECs promote occlusive pulmonary arteriopathy and severe PH. These primitive EC clones further give rise to cells of endothelial and mesenchymal lineage as directed by BMP and TGF-β signaling.

Heat shock protein 90 is downregulated in calcific aortic valve disease

Background

Calcific aortic valve disease (CAVD) is an atheroinflammatory process; finally it leads to progressive calcification of the valve. There is no effective pharmacological treatment for CAVD and many of the underlying molecular mechanisms remain unknown. We conducted a proteomic study to reveal novel factors associated with CAVD.

Methods

We compared aortic valves from patients undergoing valvular replacement surgery due to non-calcified aortic insufficiency (control group, n = 5) to a stenotic group (n = 7) using two-dimensional difference gel electrophoresis (2D-DIGE). Protein spots were identified with mass spectrometry. Western blot and immunohistochemistry were used to validate the results in a separate patient cohort and Ingenuity Pathway Analysis (IPA) was exploited to predict the regulatory network of CAVD.

Results

We detected an upregulation of complement 9 (C9), serum amyloid P-component (APCS) and transgelin as well as downregulation of heat shock protein (HSP90), protein disulfide isomerase A3 (PDIA3), annexin A2 (ANXA2) and galectin-1 in patients with aortic valve stenosis. The decreased protein expression of HSP90 was confirmed with Western blot.

Conclusions

We describe here a novel data set of proteomic changes associated with CAVD, including downregulation of the pro-inflammatory cytosolic protein, HSP90.

MKL1 promotes endothelial-to-mesenchymal transition and liver fibrosis by activating TWIST1 transcription

Excessive fibrogenic response in the liver disrupts normal hepatic anatomy and function heralding such end-stage liver diseases as hepatocellular carcinoma and cirrhosis. Sinusoidal endothelial cells contribute to myofibroblast activation and liver fibrosis by undergoing endothelial-mesenchymal transition (EndMT). The underlying mechanism remains poorly defined. Here we report that inhibition or endothelial-specific deletion of MKL1, a transcriptional modulator, attenuated liver fibrosis in mice. MKL1 inhibition or deletion suppressed EndMT induced by TGF-β. Mechanistically, MKL1 was recruited to the promoter region of TWIST1, a master regulator of EndMT, and activated TWIST1 transcription in a STAT3-dependent manner. A small-molecule STAT3 inhibitor (C188-9) alleviated EndMT in cultured cells and bile duct ligation (BDL) induced liver fibrosis in mice. Finally, direct inhibition of TWIST1 by a small-molecule compound harmine was paralleled by blockade of EndMT in cultured cells and liver fibrosis in mice. In conclusion, our data unveil a novel mechanism underlying EndMT and liver fibrosis and highlight the possibility of targeting the STAT3-MKL1-TWIST1 axis in the intervention of aberrant liver fibrogenesis.

Tight Junctions in Cell Proliferation

Tight junction (TJ) proteins form a continuous intercellular network creating a barrier with selective regulation of water, ion, and solutes across endothelial, epithelial, and glial tissues. TJ proteins include the claudin family that confers barrier properties, members of the MARVEL family that contribute to barrier regulation, and JAM molecules, which regulate junction organization and diapedesis. In addition, the membrane-associated proteins such as MAGUK family members, i.e., zonula occludens, form the scaffold linking the transmembrane proteins to both cell signaling molecules and the cytoskeleton. Most studies of TJ have focused on the contribution to cell-cell adhesion and tissue barrier properties. However, recent studies reveal that, similar to adherens junction proteins, TJ proteins contribute to the control of cell proliferation. In this review, we will summarize and discuss the specific role of TJ proteins in the control of epithelial and endothelial cell proliferation. In some cases, the TJ proteins act as a reservoir of critical cell cycle modulators, by binding and regulating their nuclear access, while in other cases, junctional proteins are located at cellular organelles, regulating transcription and proliferation. Collectively, these studies reveal that TJ proteins contribute to the control of cell proliferation and differentiation required for forming and maintaining a tissue barrier.

Role of HIF-1α-miR30a-Snai1 Axis in Neonatal Hyperoxic Lung Injury

Bronchopulmonary dysplasia (BPD) is characterized by a severe impairment in lung alveolarization and vascular development. We have previously shown that pulmonary angiogenesis is preserved in hyperoxia-exposed female mice accompanied by increased miR-30a expression, which is a proangiogenic miRNA. Also, miR-30a expression is decreased in human BPD. HIF-1α plays an essential role in postnatal lung development, especially in recovery from hyperoxic injury. Snai1 activation promotes pathological fibrosis through many mechanisms including Endo-MT, which may in turn adversely impact lung vascular development. Our objective was to test the hypothesis that higher miR-30a expression through HIF-1α decreases Snai1 expression in females and attenuates injury in the developing lung. Neonatal male and female mice (C57BL/6) were exposed to hyperoxia (P1-5, 0.95 FiO₂) and euthanized on P21. Neonatal human pulmonary microvascular endothelial cells (HPMECs; 18-24-week gestation donors; 3/group either sex) were subjected to hyperoxia (95% O₂ and 5% CO₂) or normoxia (air and 5% CO₂) up to 72 h. Snai1 expression was measured in HPMECs in vitro and in neonatal mouse lungs in vivo. Also, Snai1 expression was measured in HPMECs after miR-30a mimic and miR-30a inhibitor treatment. To further establish the potential regulation of miR-30a by Hif-1α, miR-30a expression after Hif-1α inhibition was measured in HPMECs. In vivo, Snai1 expression was decreased in neonatal female lungs compared to males at P7. Increased Snai1 expression was seen in male HPMECs upon exposure to hyperoxia in vitro. Treatment with the miR-30a mimic decreased Snai1 expression in HPMECs, while miR-30a inhibition significantly increased Snai1 expression in HPMECs. siRNA-mediated loss of Hif-1α expression in HPMECs decreased miR-30a expression. Hif-1α may lead to differential sex-specific miR-30a expression and may contribute to protection from hyperoxic lung injury in female neonatal mice through decreased Snai1 expression.

Down-regulation of miR-204 attenuates endothelial-mesenchymal transition by enhancing autophagy in hypoxia-induced pulmonary hypertension

Pulmonary arterial remodeling is a crucial cause of increased pulmonary artery pressure during pulmonary hypertension (PH). Recently, growing evidence has upheld the contribution of endothelial-mesenchymal transition (EndMT) to pulmonary arterial remodeling, but the underlying mechanisms remain largely unaddressed. miR-204 has been implicated in PH, being anti-proliferative and pro-apoptotic in pulmonary artery smooth muscles cells (PASMCs), but its role in EndMT is still unknown. Here we found that miR-204 was down-regulated by hypoxia in rat pulmonary arterial intima and human pulmonary artery endothelial cells (HPAECs), and its further down-regulation by using miR-204 inhibitor suppressed hypoxia-induced EndMT. Moreover, autophagy, evoked by hypoxia in rat pulmonary arterial intima and HPAECs, suppressed hypoxia-induced EndMT via p62-dependent degradation of Snail and Twist. Additionally, autophagy was regulated by miR-204 targeting ATG7. While down-regulation of miR-204 in PASMCs reportedly promoted monocrotaline-induced pulmonary arterial hypertension via increased cell proliferation, our data suggested an important, albeit dichotomous, role of miR-204 down-regulation in endothelial cells in the process of EndMT that it attenuated EndMT by enhancing autophagy, thereby ameliorating hypoxia-induced PH to some extent.

Adipose tissue-derived stromal cells' conditioned medium modulates endothelial-mesenchymal transition induced by IL-1β/TGF-β2 but does not restore endothelial function

Objectives

Endothelial cells undergo TGF‐β–driven endothelial‐mesenchymal transition (EndMT), representing up to 25% of cardiac myofibroblasts in ischaemic hearts. Previous research showed that conditioned medium of adipose tissue–derived stromal cells (ASC‐CMed) blocks the activation of fibroblasts into fibrotic myofibroblasts. We tested the hypothesis that ASC‐CMed abrogates EndMT and prevents the formation of adverse myofibroblasts.

Materials and methods

Human umbilical vein endothelial cells (HUVEC) were treated with IL‐1β and TGF‐β2 to induce EndMT, and the influence of ASC‐CMed was assessed. As controls, non‐treated HUVEC or HUVEC treated only with IL‐1β in the absence or presence of ASC‐CMed were used. Gene expression of inflammatory, endothelial, mesenchymal and extracellular matrix markers, transcription factors and cell receptors was analysed by RT‐qPCR. The protein expression of endothelial and mesenchymal markers was evaluated by immunofluorescence microscopy and immunoblotting. Endothelial cell function was measured by sprouting assay.

Results

IL‐1β/TGF‐β2 treatment induced EndMT, as evidenced by the change in HUVEC morphology and an increase in mesenchymal markers. ASC‐CMed blocked the EndMT‐related fibrotic processes, as observed by reduced expression of mesenchymal markers TAGLN (P = 0.0008) and CNN1 (P = 0.0573), as well as SM22α (P = 0.0501). The angiogenesis potential was impaired in HUVEC undergoing EndMT and could not be restored by ASC‐CMed.

Conclusions

We demonstrated that ASC‐CMed reduces IL‐1β/TGF‐β2‐induced EndMT as observed by the loss of mesenchymal markers. The present study supports the anti‐fibrotic effects of ASC‐CMed through the modulation of the EndMT process.

Reactive Oxygen Species (ROS), Intimal Thickening, and Subclinical Atherosclerotic Disease

Arteriosclerosis causes significant morbidity and mortality worldwide. Central to this process is the development of subclinical non-atherosclerotic intimal lesions before the appearance of pathologic intimal thickening and advanced atherosclerotic plaques. Intimal thickening is associated with several risk factors, including oxidative stress due to reactive oxygen species (ROS), inflammatory cytokines and lipid. The main ROS producing systems in-vivo are reduced nicotinamide dinucleotide phosphate (NADPH) oxidase (NOX). ROS effects are context specific. Exogenous ROS induces apoptosis and senescence, whereas intracellular ROS promotes stem cell differentiation, proliferation, and migration. Lineage tracing studies using murine models of subclinical atherosclerosis have revealed the contributory role of medial smooth muscle cells (SMCs), resident vascular stem cells, circulating bone-marrow progenitors and endothelial cells that undergo endothelial-mesenchymal-transition (EndMT). This review will address the putative physiological and patho-physiological roles of ROS in controlling vascular cell fate and ROS contribution to vascular regeneration and disease progression.

Endothelial-to-Mesenchymal Transition (EndoMT): Roles in Tumorigenesis, Metastatic Extravasation and Therapy Resistance

Cancer cells evolve in a very complex tumor microenvironment, composed of several cell types, among which the endothelial cells are the major actors of the tumor angiogenesis. Today, these cells are also characterized for their plasticity, as endothelial cells have demonstrated their potential to modify their phenotype to differentiate into mesenchymal cells through the endothelial-to-mesenchymal transition (EndoMT). This cellular plasticity is mediated by various stimuli including transforming growth factor-β (TGF-β) and is modulated dependently of experimental conditions. Recently, emerging evidences have shown that EndoMT is involved in the development and dissemination of cancer and also in cancer cell to escape from therapeutic treatment. In this review, we summarize current updates on EndoMT and its main induction pathways. In addition, we discuss the role of EndoMT in tumorigenesis, metastasis, and its potential implication in cancer therapy resistance.

Reciprocal enhancement of thrombosis by endothelial-to-mesenchymal transition induced by iliac vein compression

AIMS

Endothelial-to-mesenchymal transition (EndMT) is a pathophysiological change of vascular endothelium commonly seen in the cardiovascular system. Iliac vein compression syndrome (IVCS) is known to be often associated with intimal hyperplasia and thrombosis. However, whether EndMT exists in IVCS has not yet been reported. The purpose of this study was to investigate the relationship between EndMT and thrombosis in IVCS.

MAIN METHODS

Using IVCS models in pig and mouse, we detected intimal changes and thrombus in stenotic iliac vein by immunofluorescence staining. Primary human umbilical vein endothelial cells (HUVEC) were stimulated by transforming growth factor β1 (TGF-β1) and thrombin, and cell phenotypic transition and antithrombotic function of HUVEC were examined through q-PCR, western blot and ELISA. In the end, by immunofluorescence staining, we observed the effect of anticoagulant on interstitial changes of venous endothelial cells in IVCS models.

KEY FINDINGS

We showed that iliac vein compression induced EndMT, of which its inhibition reduced thrombus formation. Further studies showed that HUVECs undergoing EndMT lost their anticoagulation and thrombolytic function. Interestingly, thrombin aggravated EndMT through TGF-β/Smad3 signaling. Moreover, compared with wild type (WT) mice, EndMT in stenotic iliac vein was reduced in WT mice fed with rivaroxaban or factor VII knockout mice, implying that anticoagulation alleviated EndMT in IVCS models.

SIGNIFICANCE

Our findings indicate that EndMT and thrombosis reinforce reciprocally in IVCS, implying that targeting EndMT could be a potential strategy in prevention and treatment of thrombosis in IVCS.

Inhibition of prostaglandin E2 receptor 4 by lnc000908 to promote the endothelial-mesenchymal transition participation in cardiac remodelling

Long non‐coding RNAs (lncRNAs) have emerged as potent regulators of cardiac disease; however, the role of lncRNA in cardiac fibrosis remains partially understood. In this study, we identified a cardiac endothelial‐enriched lncRNA‐lnc000908, which was markedly up‐regulated in rats with cardiac fibrosis. In addition, the expression of prostaglandin E2 receptor 4 (EP4) was decreased in cardiac fibrosis. In vivo lnc000908 silencing by lentivirus increased the EP4 level, decreased endothelial‐mesenchymal transition (EndMT) and improved cardiac fibrosis and cardiac function. Consistently, the lnc000908 knockdown also up‐regulated EP4 and suppressed transforming growth factor‐beta (TGF‐β)‐induced EndMT in cardiac microvascular endothelial cells. In contrast, the lnc000908 overexpression by lentivirus decreased the EP4 level and induced EndMT. Of note, these pro‐ or anti‐EndMT effects were reversed by the EP4 overexpression or the EP4 antagonist AH‐23848, respectively. This study demonstrates that lnc000908 is a novel regulator of cardiac fibrosis by modulating the EP4 expression and EndMT.

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.

Liraglutide Inhibits Endothelial-to-Mesenchymal Transition and Attenuates Neointima Formation after Endovascular Injury in Streptozotocin-Induced Diabetic Mice

Hyperglycaemia causes endothelial dysfunction, which is the initial process in the development of diabetic vascular complications. Upon injury, endothelial cells undergo an endothelial-to-mesenchymal transition (EndMT), lose their specific marker, and gain mesenchymal phenotypes. This study investigated the effect of liraglutide, a glucagon-like peptide 1 (GLP-1) receptor agonist, on EndMT inhibition and neointima formation in diabetic mice induced by streptozotocin. The diabetic mice with a wire-induced vascular injury in the right carotid artery were treated with or without liraglutide for four weeks. The degree of neointima formation and re-endothelialisation was evaluated by histological assessments. Endothelial fate tracing revealed that endothelium-derived cells contribute to neointima formation through EndMT in vivo. In the diabetic mouse model, liraglutide attenuated wire injury-induced neointima formation and accelerated re-endothelialisation. In vitro, a high glucose condition (30 mmol/L) triggered morphological changes and mesenchymal marker expression in human umbilical vein endothelial cells (HUVECs), which were attenuated by liraglutide or Activin receptor-like 5 (ALK5) inhibitor SB431542. The inhibition of AMP-activated protein kinase (AMPK) signaling by Compound C diminished the liraglutide-mediated inhibitory effect on EndMT. Collectively, liraglutide was found to attenuate neointima formation in diabetic mice partially through EndMT inhibition, extending the potential therapeutic role of liraglutide.

Activated Fibroblast Program Orchestrates Tumor Initiation and Progression; Molecular Mechanisms and the Associated Therapeutic Strategies

: Neoplastic epithelial cells coexist in carcinomas with various non-neoplastic stromal cells, together creating the tumor microenvironment. There is a growing interest in the cross-talk between tumor cells and stromal fibroblasts referred to as carcinoma-associated fibroblasts (CAFs), which are frequently present in human carcinomas. CAF populations extracted from different human carcinomas have been shown to possess the ability to influence the hallmarks of cancer. Indeed, several mechanisms underlying CAF-promoted tumorigenesis are elucidated. Activated fibroblasts in CAFs are characterized as alpha-smooth muscle actin-positive myofibroblasts and actin-negative fibroblasts, both of which are competent to support tumor growth and progression. There are, however, heterogeneous CAF populations presumably due to the diverse sources of their progenitors in the tumor-associated stroma. Thus, molecular markers allowing identification of bona fide CAF populations with tumor-promoting traits remain under investigation. CAFs and myofibroblasts in wound healing and fibrosis share biological properties and support epithelial cell growth, not only by remodeling the extracellular matrix, but also by producing numerous growth factors and inflammatory cytokines. Notably, accumulating evidence strongly suggests that anti-fibrosis agents suppress tumor development and progression. In this review, we highlight important tumor-promoting roles of CAFs based on their analogies with wound-derived myofibroblasts and discuss the potential therapeutic strategy targeting CAFs.