Endothelial-mesenchymal Transition Research Articles

Construction of tissue-engineered vascular grafts with enhanced patency by integrating heparin, cell-adhesive peptide, and carbon monoxide nanogenerators into acellular blood vessels

Small-diameter tissue-engineered vascular grafts (sdTEVGs) have garnered significant attention as a potential treatment modality for vascular bypass grafting and replacement therapy. However, the intimal hyperplasia and thrombosis are two major complications that impair graft patency during transplantation. To address this issue, we fabricated the covalent-organic framework (COF)-based carbon monoxide (CO) nanogenerator-and co-immobilized with LXW-7 peptide and heparin to establish a multifunctional surface on TEVGs constructed from acellular blood vessels for preventing thrombosis and stenosis. The cell-adhesive peptide LXW-7 could capture endothelial-forming cells (EFCs) to promote endothelialization, while the antithrombotic molecule heparin prevented thrombus formation. The reactive oxygen species (ROS)-triggered CO release suppressed the adhesion and activation of macrophages, leading to the reduction of ROS and inflammatory factors. As a result, the endothelial-to-mesenchymal transition (EndMT) triggered by inflammation was restricted, facilitating the maintenance of the homeostasis of the neo-endothelium and preventing pathological remodeling in TEVGs. When transplanted in vivo, these vascular grafts exhibited negligible intimal hyperplasia and remained patent for 3 months. This achievement provided a novel approach for constructing antithrombotic and anti-hyperplastic TEVGs.

MiR-23b-3p Ameliorates LPS-Induced Pulmonary Fibrosis by Inhibiting EndMT via DPP4 Inhibition.

Acute respiratory distress syndrome is a disease triggered by severe pulmonary and systemic inflammation that may lead to fibrosis and the decline of lung function. Lung capillary endothelial-to-mesenchymal transition (EndMT) is one of the primary sources of fibroblasts in pulmonary fibrosis. The role of miRNAs as molecular markers of pulmonary fibrosis, and miRNAs as nucleic acid drugs has attracted increasing attention. To mock EndMT process, Human pulmonary microvascular endothelial cells (HPMECs) were induced with lipopolysaccharide (LPS). Similarly, LPS treatment was used to generate a mouse model of LPS-induced EndMT and pulmonary fibrosis. LPS-induced EndMT in HPMECs resulted in a significant reduction of miR-23b-3p. miR-23b-3p inhibited the interstitial transition of HPMECs, and miR-23b-3p could mediate this process via inhibiting dipeptidyl peptidase-4 (DPP4). Dual-luciferase assays confirmed the regulatory mechanism of miR-23b-3p. In our mouse model of LPS-induced pulmonary fibrosis, miR-23b-3p and a DPP4 inhibitor (sitagliptin) individually alleviated LPS-induced EndMT progression and pulmonary fibrosis, and their combined use achieved the strongest remission effect. To sum up, miR-23b-3p alleviates EndMT in pulmonary fibrosis by inhibiting the expression of DPP4.

CD40 is expressed in the subsets of endothelial cells undergoing partial endothelial-mesenchymal transition in tumor microenvironment.

Tumor progression and metastasis are regulated by endothelial cells undergoing endothelial-mesenchymal transition (EndoMT), a cellular differentiation process in which endothelial cells lose their properties and differentiate into mesenchymal cells. The cells undergoing EndoMT differentiate through a spectrum of intermediate phases, suggesting that some cells remain in a partial EndoMT state and exhibit an endothelial/mesenchymal phenotype. However, detailed analysis of partial EndoMT has been hampered by the lack of specific markers. Transforming growth factor-β (TGF-β) plays a central role in the induction of EndoMT. Here, we showed that inhibition of TGF-β signaling suppressed EndoMT in a human oral cancer cell xenograft mouse model. By using genetic labeling of endothelial cell lineage, we also established a novel EndoMT reporter cell system, the EndoMT reporter endothelial cells (EMRECs), which allow visualization of sequential changes during TGF-β-induced EndoMT. Using EMRECs, we characterized the gene profiles of multiple EndoMT stages and identified CD40 as a novel partial EndoMT-specific marker. CD40 expression was upregulated in the cells undergoing partial EndoMT, but decreased in the full EndoMT cells. Furthermore, single-cell RNA sequencing analysis of human tumors revealed that CD40 expression was enriched in the population of cells expressing both endothelial and mesenchymal cell markers. Moreover, decreased expression of CD40 in EMRECs enhanced TGF-β-induced EndoMT, suggesting that CD40 expressed during partial EndoMT inhibits transition to full EndoMT. The present findings provide a better understanding of the mechanisms underlying TGF-β-induced EndoMT and will facilitate the development of novel therapeutic strategies targeting EndoMT-driven cancer progression and metastasis.

Multiscale computational modeling of aortic valve calcification.

Calcific aortic valve disease (CAVD) is a common cardiovascular disease that affects millions of people worldwide. The disease is characterized by the formation of calcium nodules on the aortic valve leaflets, which can lead to stenosis and heart failure if left untreated. The pathogenesis of CAVD is still not well understood, but involves several signaling pathways, including the transforming growth factor beta (TGF ) pathway. In this study, we developed a multiscale computational model for TGF -stimulated CAVD. The model framework comprises cellular behavior dynamics, subcellular signaling pathways, and tissue-level diffusion fields of pertinent chemical species, where information is shared among different scales. Processes such as endothelial to mesenchymal transition (EndMT), fibrosis, and calcification are incorporated. The results indicate that the majority of myofibroblasts and osteoblast-like cells ultimately die due to lack of nutrients as they become trapped in areas with higher levels of fibrosis or calcification, and they subsequently act as sources for calcium nodules, which contribute to a polydispersed nodule size distribution. Additionally, fibrosis and calcification processes occur more frequently in regions closer to the endothelial layer where the cell activity is higher. Our results provide insights into the mechanisms of CAVD and TGF signaling and could aid in the development of novel therapeutic approaches for CAVD and other related diseases such as cancer. More broadly, this type of modeling framework can pave the way for unraveling the complexity of biological systems by incorporating several signaling pathways in subcellular models to simulate tissue remodeling in diseases involving cellular mechanobiology.

Neovascularization directed by CAVIN1/CCBE1/VEGFC confers TMZ-resistance in glioblastoma

Acquisition of resistance to temozolomide (TMZ) poses a significant challenge in glioblastoma (GBM) therapy. Neovascularization, a pivotal process in tumorigenesis and development, remains poorly understood in its contribution to chemoresistance in GBMs. This study unveils aberrant vascular networks within TMZ-resistant (TMZ-R) GBM tissues and identifies the extracellular matrix (ECM) protein CCBE1 as a potential mediator. Through in vivo and in vitro experiments involving gain and loss of function assessments, we demonstrate that high expression of CCBE1 promotes hyper-angiogenesis and orchestrates partial endothelial-to-mesenchymal transition (EndMT) in human microvascular endothelial cells (HCMEC/d3) within GBM. This is likely driven by VEGFC/Rho signaling. Intriguingly, CCBE1 overexpression substantially fails to promote tumor growth, but endows resistance to GBM cells in a vascular endothelial cell-dependent manner. Mechanically, the constitutive phosphorylation of SP1 at Ser101 drives the upregulation of CCBE1 transcription in TMZ resistant tumors, and the excretion of CCBE1 depends on caveolae associated protein 1 (CAVIN1) binding and assembling. Tumor cells derived CCBE1 promotes VEGFC maturation, activates VEGFR2/VEGFR3/Rho signaling in vascular endothelial cells, and ultimately results in hyper-angiogenesis in TMZ-R tumors. Collectively, the current study uncovers the cellular and molecular basis of abnormal angiogenesis in a chemo resistant microenvironment, implying that curbing CCBE1 is key to reversing TMZ resistance.

Maternal exposure to nano-titanium dioxide impedes fetal development via endothelial-to-mesenchymal transition in the placental labyrinth in mice

BackgroundExtensive production and usage of commercially available products containing TiO2 NPs have led to accumulation in the human body. The deposition of TiO2 NPs has even been detected in the human placenta, which raises concerns regarding fetal health. Previous studies regarding developmental toxicity have frequently focused on TiO2 NPs < 50 nm, whereas the potential adverse effects of large-sized TiO2 NPs received less attention. Placental vasculature is essential for maternal–fetal circulatory exchange and ensuring fetal growth. This study explores the impacts of TiO2 NPs (100 nm in size) on the placenta and fetal development and elucidates the underlying mechanism from the perspective of placental vasculature. Pregnant C57BL/6 mice were exposed to TiO2 NPs by gavage at daily dosages of 10, 50, and 250 mg/kg from gestational day 0.5–16.5.ResultsTiO2 NPs penetrated the placenta and accumulated in the fetal mice. The fetuses in the TiO2 NP-exposed groups exhibited a dose-dependent decrease in body weight and length, as well as in placental weight and diameter. In vivo imaging showed an impaired placental barrier, and pathological examinations revealed a disrupted vascular network of the labyrinth upon TiO2 NP exposure. We also found an increase in gene expression related to the transforming growth factor-β (TGF-β) -SNAIL pathway and the upregulation of mesenchymal markers, accompanied by a reduction in endothelial markers. In addition, TiO2 NPs enhanced the gene expression responsible for the endothelial-to-mesenchymal transition (EndMT) in cultured human umbilical vein endothelial cells, whereas SNAIL knockdown attenuated the induction of EndMT phenotypes.ConclusionOur study revealed that maternal exposure to 100 nm TiO2 NPs disrupts placental vascular development and fetal mice growth through aberrant activation of EndMT in the placental labyrinth. These data provide novel insight into the mechanisms of developmental toxicity posed by NPs.

Understanding how MSCs reverse radiation-induced fibrosis: HGF vs. TGF-B1

Understanding how MSCs reverse radiation-induced fibrosis: HGF <i>vs.</i> TGF-B1

Abstract LB_C18: A novel WNT-RIP1 signaling pathway promotes colorectal cancer metastasis via induction of EMT

Abstract We identified new potential roles of RIP1 (receptor-interacting protein kinase 1) in controlling WNT signaling to enhance metastasis of colorectal cancer (CRC). First, we showed that WNT3A treatment sequentially increased the expression of RIP1 and β-catenin. Next, Immunohistochemical analyses of human CRC tissue arrays consisting of normal, primary, and metastatic cancers showed that elevated RIP1 expression might be related to β-catenin expression and it also indicated inductions of carcinogenesis and metastasis. In in vivo experiments with mice, intravenous injection of RIP1 over-expressed CRC cells has demonstrated that RIP1 may promote metastasis. These results implied RIP1 might be major component of WNT signaling. Next, we performed immunoprecipitation (IP) to revealed intracellular signaling mechanism that WNT3A treatment could induce direct binding between RIP1 and β-catenin, and observed direct binding and stabilization of the β-catenin protein via regulation of RIP1 ubiquitination by a downregulation of the E3 ligase, cIAP1/2. Down-regulation of cIAP1/2 expression with siRNA treatment and inhibition of its ubiquitinase activity with pharmacological inhibitor treatment could enhance WNT3A-induced RIP1 and β-catenin protein expression and binding. These results also enhance the migration and invasion of CRC cells in vitro via induction of endothelial-mesenchymal transition (EMT). The in vitro binding assay and IP of exogenous RIP1-containing CRC cells additionally result in the direct binding of RIP1 and β-catenin. The enhanced RIP1 expression can destroy the β-catenin–β-TrCP complex. Additionally, we also identified GDF15 (Growth and differentiation factor 15) is located at down-stream of WNT3A-RIP1 pathway and involved in EM induction. Taken together, these results suggest an identification of novel WNT-RIP1 pathway to enhance EMT and suggest GDF15 also might contribute CRC malignancy. Citation Format: A-RAM KANG, DO HOON KIM, JONG KUK PARK. A novel WNT-RIP1 signaling pathway promotes colorectal cancer metastasis via induction of EMT [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr LB_C18.

Baicalin attenuates pulmonary vascular remodeling by inhibiting calpain-1 mediated endothelial-to-mesenchymal transition

BackgroundPrevious studies have demonstrated the beneficial effect of baicalin on pulmonary arterial hypertension (PAH), but the mechanism is unclear. AimThe aim of the present study was to evaluate the effect of baicalin on pulmonary vascular remodeling (PVR) with a focus on calpain-1-mediated endothelial-to-mesenchymal transition (EndMT). MethodsPAH was induced by intraperitoneal injection of monocrotaline (MCT) in rats and hypoxia in calpain-1 gene knockout (Capn1−/−) and wild-type C57BL/6 mice. An in vitro PVR model was established in PASMCs and HPAECs. ResultsThe data showed that baicalin treatment and calpain-1 inhibition alleviated MCT and hypoxia-induced increases in right ventricular systolic pressure (RVSP), prevented right ventricle hypertrophy and PVR, and attenuated cardiopulmonary fibrosis. Moreover, baicalin ameliorated PAH-induced EndMT, as evidenced by the suppressed expression of mesenchymal markers vimentin, and α-SMA and restored expression of endothelial markers CD31, and VE-cadherin. In vitro studies showed that baicalin treatment blocked TGF-β1-induced EndMT in HPAECs and abolished hypoxia-induced PASMC proliferation and migration. All the beneficial effects of baicalin on PVR in vitro and in vivo were accompanied by suppressed calpain-1 expression. Further study demonstrated that baicalin treatment and calpain-1 inhibition inhibited the enhanced expression of PI3K and p-AKT both in vitro and in vivo. ConclusionsIn conclusion, baicalin treatment attenuates PVR by inhibiting calpain-1 and PI3K/Akt-mediated EndMT.

Human placental vascular and perivascular cell heterogeneity differs between first trimester and term, and in pregnancies affected by foetal growth restriction.

Growth-restricted placentae have a reduced vascular network, impairing exchange of nutrients and oxygen. However, little is known about the differentiation events and cell types that underpin normal/abnormal placental vascular formation and function. Here, we used 23-colour flow cytometry to characterize placental vascular/perivascular populations between first trimester and term, and in foetal growth restriction (FGR). First-trimester endothelial cells had an immature phenotype (CD144+/lowCD36-CD146low), while term endothelial cells expressed mature endothelial markers (CD36+CD146+). At term, a distinct population of CD31low endothelial cells co-expressed mesenchymal markers (CD90, CD26), indicating a capacity for endothelial to mesenchymal transition (EndMT). In FGR, compared with normal pregnancies, endothelial cells constituted 3-fold fewer villous core cells (P < 0.05), contributing to an increased perivascular: endothelial cell ratio (2.6-fold, P < 0.05). This suggests that abnormal EndMT may play a role in FGR. First-trimester endothelial cells underwent EndMT in culture, losing endothelial (CD31, CD34, CD144) and gaining mesenchymal (CD90, CD26) marker expression. Together this highlights how differences in villous core cell heterogeneity and phenotype may contribute to FGR pathophysiology across gestation.

Interferon-Alpha Impairs Neoplastic Vasculogenesis in a 3D iPSC-Based Model of JAK2V617F+ Myeloproliferative Neoplasms

Overt Myelofibrosis (MF) is an end-stage subtype of BCR-ABL1 negative myeloproliferative neoplasms (MPN), which is characterized by progressive bone marrow (BM) fibrosis resulting in loss of normal hematopoietic support as well as inflammatory and vascular complications. While aberrant neoangiogenesis is known to participate in the pathogenesis of MF, Erba et al. (Am J Pathol, 2017) suggested the occurrence of endothelial-to-mesenchymal transition (EndMT) in BM and spleen of MF patients (pts). Given the relevance of endothelial cells (EC) for MF development and the occurrence of JAK2V617F-mutated EC in MPN pts, targeting of the vascular niche has emerged as a promising therapeutic strategy. To untangle the impact of the JAK2V617F mutation on human vasculogenesis, we leveraged high-purity and clonal patient-specific induced pluripotent stem cell (iPSC)-derived EC (iEC) harboring either the JAK2V617F mutation in hetero- (JAK2V617F HET) or homozygosis (JAK2V617F HOM). JAK2 WT and CRISPR-repaired isogenic JAK2 WT (both referred to as JAK2 WT) were used as controls. In a first set of in vitro experiments, JAK2V617F mutated iEC showed a significantly increased proliferation rate in comparison to JAK2 WT iEC. We next evaluated the effect of selected drugs on iEC viability to assess their vascular toxicity. While treatment with 1 µM each of fedratinib, anagrelide or venetoclax led to a decrease in iEC viability (all **p ≤ .01), no significant alterations were observed with 1 µM ruxolitinib (RUX) or 1000 U/ml interferon-alpha (IFNa). Overall, no differences between the 3 genotypes were observed, pointing towards a genotype-independent mode of action. Given the favorable vascular toxicity profile of IFNa, as shown above, its anti-angiogenic potential was then assessed via endothelial tube formation assays. Pre-incubation with 1000 U/ml IFNa prior to seeding of the cells onto a reconstituted basement membrane matrix led to a significant inhibition of capillary-like structures formation in JAK2 WT and JAK2V617F HET or HOM iEC. One of the limitations of 2D culture assays is the lack of 3D homotypic cellular organization, compromising its translational value. Therefore, we established an adaptive 3D fibrin-based model to recapitulate, in vitro, the critical EC-pericyte crosstalk required for formation and maturation of blood vessels. Recent studies highlighted the capacity of BM mesenchymal stem cells (MSC) to differentiate into pericytes. Therefore, we seeded JAK2 WT and JAK2V617F HETor HOM iEC with or without MSC in fibrin hydrogels. MSC and iEC were visualized using different PKH dyes as fluorescent cell linkers to enable live tracking of vascular tree formation. Although self-assembly of JAK2 WT and JAK2V617F HET or HOM iEC into vessel-like structures was observed in the generated monocultures, the presence of MSC in the cocultures led to a significant increase of the formed network area (Fig. 1), hence recapitulating the critical support of pericytes. While acute IFNa exposure did not alter vascular tree formation (Fig. 1), a separate pre-treatment of iEC and MSC prior to cocultivation, significantly impaired neoplastic vasculogenesis (Fig. 2). Interestingly, interactive microscopy image analysis revealed an increased MSC/iEC interaction in JAK2V617F HOM pre-treated cocultures (*p ≤ .05). Bulk RNA-sequencing of JAK2 WT and JAK2V617F HET or HOM iEC treated for 24h with 1000 U/ml showed a strong response to IFNa. Future analysis may unravel a JAK2V617F specific transcription signature. Moreover, we induced EndMT in our 3D iEC-MSC coculture model by treatment with pro-inflammatory cytokines, reflected by the loss of EC markers (e.g. Claudin 5) and upregulation of mesenchymal markers (e.g. aSMA) by immunofluorescence. We are currently evaluating the capacity of RUX vs IFNa to inhibit EndMT. In summary, we show that IFNa impairs neoplastic vasculogenesis in a robust in vitro 3D coculture system that enables precise control of cellularity and genotype. Our model is a valuable tool to decipher the poorly investigated impact of IFNa on the BM microenvironment. In addition, its translational and scalable properties (e.g. by integrating primary or iPSC-derived hematopoietic cells) will allow us to study the impact of additional drugs on MPN-associated fibrotic transformation of the BM.

Unlocking the Role of Endothelial MPL Receptor and JAK2V617F Mutation: Insights into Cardiovascular Dysfunction in MPNs and Chip

Introduction Patients with JAK2V617F-positive myeloproliferative neoplasms (MPNs) and clonal hematopoiesis of indeterminate potential (CHIP) are at a significantly higher risk of cardiovascular diseases (CVDs). Vascular endothelial cells (ECs) carrying the JAK2V617F mutation can be detected in many MPN patients. The thrombopoietin receptor MPL is expressed on vascular ECs, though its role in endothelial function is unclear. In this study, we investigated the mechanisms through which the JAK2V617F mutation induces endothelial dysfunction to accelerate CVDs, shedding light on endothelial MPL as a potential therapeutic target for preventing or mitigating cardiovascular complications in JAK2V617F-positive MPNs. Methods JAK2V617F Flip-Flop mice (FF1; provided by Dr. Radek Skoda) were crossed with VEcadherin-creERT2 mice (CDH5) to generate CDH5 +/-FF1 +/- mice, which can be induced by tamoxifen to express human JAK2V617F specifically in vascular ECs but not in blood cells. MPL fl mice (provided by Dr. Warren Alexander) were crossed with CDH5 +FF1 + mice to generate CDH5 +FF1 +MPL fl/fl mice. To validate findings in transgenic murine models in human cells, we utilized a pair of isogenic induced pluripotent stem (iPS) cell lines derived from the same MPN patient, one carrying the JAK2V617F mutation (PVB1.4) and the other being JAK2 wild-type (PVB1.11). These iPS cell lines were differentiated into human ECs using a modified iPS differentiation protocol. Results CDH5 +FF1 + mice exhibited mild thrombocytosis but no cardiac dysfunction. However, when challenged with a high-fat diet, these mice developed dilated cardiomyopathy with significant decreases in LV ejection fraction and increases in LV end-diastolic and end-systolic volumes. Pathological evaluation revealed the presence of thromboses in segment pulmonary arteries and scattered coronary capillaries. There was intimal thickening, smooth muscle cell thickening, and perivascular fibrosis of scattered coronary arterioles in CDH5 +FF1 + mice compared to control mice. These findings, along with impaired cardiac EC function (measured by angiogenesis in vitro) and loss of EC markers, as well as significant enrichment of gene expression signatures associated with inflammatory response and epithelial-mesenchymal transition in JAK2V617F mutant cardiac ECs, suggest that the JAK2V617F mutation induces endothelial-to-mesenchymal transition (EndMT) in cardiac ECs from the CDH5 +FF1 + mice. Similarly, JAK2 wild-type ECs derived from PVB1.11 iPS cell line maintained the expression of EC markers and the characteristic cobblestone endothelial morphology throughout serial passages in vitro; in contrast, JAK2V617F mutant ECs derived from PVB1.4 exhibited a gradual loss of EC marker expression, decreased EC function, and underwent a phenotypical transition toward a fibroblastoid morphology, providing compelling evidence of EndMT induction by the JAK2V617F mutation in human ECs. We noticed that the thrombopoietin receptor MPL is abundantly expressed in the heart's vascular endothelium, compared to other tissues (e.g., lung, marrow, spleen). MPL expression is upregulated in JAK2V617F mutant ECs compared to wild-type ECs, and Inhibiting JAK-STAT signaling using Ruxolitinib abolished this MPL upregulation. To investigate the role of endothelial TPO/MPL signaling in JAK2V617F-induced cardiovascular dysfunction, we generated CDH5 +FF1 +MPL fl/fl mice to knock down MPL in JAK2V617F-bearing vascular ECs. The CDH5 +FF1 +MPL fl/fl mice maintained normal blood counts and cardiac function even after a high-fat diet challenge. In JAK2V617F mutant human ECs derived from PVB1.4 iPS cell line, treatment with AMM2, an anti-MPL neutralizing antibody, preserved EC markers and endothelial morphology compared to untreated mutant ECs. These results demonstrated that inhibiting the endothelial MPL can suppress JAK2V617F-induced EndMT and prevent cardiovascular dysfunction caused by mutant ECs. Notably, the endothelial MPL receptor is not indispensable for the normal physiological regulation of blood cell counts and cardiac function. Conclusion Our study provides valuable insights into the increased risk of CVDs observed in patients with JAK2V617F-positive CHIP and MPNs. Further investigations into the role of EndMT in other CHIP-associated mutations may shed light on the diverse CVD risks associated with different CHIP mutations.

Single Cell Analysis of Bone Marrow Stromal Cells Shows That a Pro-Inflammatory and Stress Response Together with Polarized Differentiation of Stromal Elements Characterize the Bone Marrow Microenvironment during Multiple Myeloma Development

Current knowledge of the biological role of the non-hemopoietic components of the bone marrow (BM) niche to the pathogenesis of multiple myeloma (MM) is poorly understood. We utilized a murine model to interrogate niche forming cells early in the natural history of MM, at a precursor stage (MGUS/smoldering-like) in more detail. Studying interactions between the MM clone and the stromal components of the MM niche are challenging as they represent only approximately 0.2% of the total marrow content and are difficult to isolate. However, by isolating the stromal compartment of the BM by depleting hemopoietic cells via flow sorting combined with the use of single cell RNA sequencing (scRNA-seq) it is possible to perform an in-vivo analysis of the individual cellular components of the stromal microenvironment and to characterize their relative abundance, cellular differentiation state, and transcriptomic profile. To comprehensively assess changes in the stromal cells during the early stage of MM, 5TGM1 cells were intravenously injected into aged (6 month old) KaLwRij mice. KaLwRij mice without MM were used as controls. Stromal cells were isolated following tumor engraftment in the marrow at a precursor stage and enriched as previously described (Baryawno et al, Cell 2019). scRNA-seq was performed on 5 libraries of cells using the 10X Genomics Chromium platform. All data analysis was performed in R. After filtering out low quality cells, 45,030 cells remained for analysis. The 5 libraries were integrated with Seurat and run through a standard clustering workflow involving log-normalization, finding variable features, dimensional reduction, and clustering. Cell type annotation for each cluster was performed manually using established markers for both the stromal and immune compartments. After excluding immune cell populations, 14,219 cells remained. Select subpopulations were re-clustered by isolating the cell types of interest and running them through separate standard clustering workflows. For each population of interest, differentially expressed genes were determined using the Wilcox rank sum test in Seurat, trajectory analysis and pseudotime were computed using Monocle3, and enriched gene sets were computed using GSEAPreranked. We identified 7 distinct populations of stromal cells including mesenchymal stromal cells (MSCs) ( Lepr, Adipoq, and Cxcl12), osteo-lineage cells (OLCs) ( Bglap, Spp1, and Sp7), fibroblasts ( S100a4, Fn1, and Dcn), chondrocytes ( Col2a1, Sox9, and Acan), pericytes ( Acta2, Myh11, and Mcam), and two endothelial cell (ECs) populations, arterial (AEC) and sinusoidal (SEC) ( Cdh5, Cd34, and Pecam1). Compared to normal BM, MM engraftment was associated with numerical differences in stromal cell populations between normal and MM. Gene set enrichment analysis showed an inflammatory and oxidative stress signal associated with the MM microenvironment. Sub-clustering analysis showed MSC differentiation was polarized away from osteocyte formation towards adipocytes with the identification of a novel population only seen in MM. Bone marrow endothelial cell populations were also substantially altered at this early disease stage, with differentiation polarized towards sinusoidal endothelial cells generating a pro-angiogenic /pro-inflammatory phenotype. An increase in cells undergoing endothelial to mesenchymal transition (EndMT) was also present. Taken together, we show, for the first time, existence of remodeling of the stromal populations induced by the MM clone characterized by a pro-inflammatory phenotype together with polarized differentiation. These changes result in the expansion of a number of key populations that increase the MM niche contributing to growth and survival signals and shaping of the content of the immune microenvironment. These changes result in a self-perpetuating signaling loop between cells, which needs to be broken therapeutically in order to stop progression, induce remission and long-term disease outcomes. Conclusion - In early stages of MM pathogenesis, MM cells remodel the stromal microenvironment by altering the amount and function of MSCs and endothelial cells. Through favoring an adipocytic fate of MSCs, endothelial mesenchymal transition and altering the balance between arterial and sinusoidal endothelial cells, MM cells promote an inflammatory environment that contributes to MM development and progression.

TMIC-55. TURNING ENEMY INTO ALLY: HIJACK BRAIN TUMOR CELLS TO BREAK DOWN THE BLOOD-TUMOR BARRIER

Abstract A major obstacle in brain cancer treatment is the blood-tumor barrier (BTB), which limits the delivery of a vast majority of therapeutic agents. Medulloblastoma (MB), the most common pediatric malignant brain tumor, consists of four subgroups (WNT, SHH, Group 3, Group 4). Increasing BTB permeability of non-WNT MB is essential for effectively treating patients by overcoming this drug delivery impediment. Since the BTB is exposed to biofluids such as blood and brain interstitial fluid, which present dynamic osmotic challenges, we hypothesized that cell volume regulation plays a crucial role in BTB integrity. Using a genetically engineered mouse model of SHH MB, we show that tumor-specific knockout of volume-regulated ion channel, Lrrc8a, significantly increases BTB permeability and enhances the therapeutic response of MB-bearing mice to vismodegib, an FDA-approved antagonist of the SHH pathway. Lrrc8a-deficient tumor cells develop ectopic contact with blood vessels, permitting tumor cell-derived Tgfβ2 to activate Tgfβ signaling in endothelial cells. Consequently, endothelial cells in Lrrc8a knockout MB lose endothelial characteristics and gain mesenchymal features, indicative of Tgfβ signaling-induced endothelial-mesenchymal transition (EndMT). Furthermore, tumor-specific LRRC8A knockdown enhances BTB permeability in a xenograft human Group 3 MB model. Collectively, our findings establish Lrrc8a/LRRC8A as a therapeutic target to increase the therapy response of MB and provide evidence that inducing EndMT could be a strategy for enhancing BTB permeability to treat brain cancer.

RNA elongation contributes to gene expression regulation during early endothelial-to-mesenchymal transition

Abstract Background Endothelial dysfunction is characterized by endothelial-to-mesenchymal transition (EndMT), a process in which endothelial cells (EC) transform into mesenchymal cells and lose part of their endothelial identity. EndMT-positive cells are present in vulnerable atherosclerotic plaques. EndMT is triggered by stress stimuli such as inflammation or hypoxia that require an adaptive change in gene expression mediated at the level of RNA elongation. RNA elongation is controlled by the super elongation complex (SEC), which is built around scaffolding proteins of the AF family (AFF1-AFF4). The SEC controls the pausing of RNA Polymerase II (RNAPII). We hypothesized that RNA elongation plays a regulatory role in EndMT. Methods and Results Single cell sequencing data revealed that the SEC scaffold proteins AFF1 and AFF4 are ubiquitously expressed in human carotid artery plaques. AFF1 and AFF4 are higher expressed in EC compared to AFF2 and AFF3. In an in vitro EndMT model, AFF1 and AFF4 were upregulated compared to controls (AFF1: 1.9-fold; AFF4: 2.6-fold). SEC inhibition using chemical compounds reduced the protein levels of AFF1 (-67.4%) and AFF4 (-46.5%). EndMT induction was reduced by SEC inhibition, as measured by mesenchymal marker gene expression (SM22: -88.8%; CNN1: -94.0%). The rapid induction of gene expression depends on the release of paused RNAPII present at the promoter site. ChIP-sequencing revealed a reduced occupancy of RNAPII at promoter sites in EndMT as early as 2 h compared to controls, suggesting a rapid pause release of RNAPII during EndMT. Indeed, transcriptome-wide RNA elongation rates were increased by 20.2% as early as 10 min after induction of EndMT, as determined by analysis of newly synthesized 4sU-labelled RNA. SEC inhibition reduced transcriptome-wide RNA elongation rates (-26.8%). These data suggest a regulatory contribution of RNA elongation in early EndMT. Among the genes that were immediately and prominently upregulated after the induction of EndMT was the SPARC mRNA. RNA initiation and elongation of SPARC mRNA was increased 10 min after EndMT induction, which was reduced by SEC inhibition. 72 hours after EndMT induction, inhibition of SEC resulted in a reduction in SPARC mRNA (-72.2%), protein concentration (-97.2%) and reduced SPARC delivery to the supernatant (-43.9%). Knockdown of SPARC enhanced EndMT induction (SM22: 1.6-fold; CNN1: 3.6-fold), which was attenuated by treatment with recombinant SPARC. Conclusions We observed increased RNA elongation rates during EndMT associated with decreased pausing of RNA Polymerase II. The RNA elongation mediated specific gene expression such as the upregulation of SPARC. Taken together, our results indicate that RNA elongation plays a regulatory role in EndMT.

Long noncoding RNA H19 is elevated in aortic valve stenosis and governs antigenic response and valvular endothelial cell phenotypes through endothelial to mesenchymal transition

Abstract Background Long noncoding RNAs (lncRNAs) have emerged as important regulators of cardiovascular disease, including aortic valve stenosis (AVS). Endothelial to mesenchymal transition (EndMT) is a transdifferentiation process that is associated with the development of AVS in the elderly population. Although several recent studies have reported that lncRNAs are dysregulated and might play a crucial role in EndMT, no specific role of lncRNA was reported in AVS pathogenesis. Here, we sought to investigate the role of H19 in EndMT during the pathogenesis of AVS. Methods and results High-throughput lncRNA sequencing of human aortic valve tissue explanted from patients with AVS due to severe stenosis during surgical aortic valve replacement (SAVR) demonstrated that certain lncRNAs [H19, AGAP2-AS1 (PUNISHER), GAS5, MALAT1] are significantly dysregulated compared to patients without AVS. To validate the RNA-seq data, 60 patients with AVS (n=30) or without AVS (n=30) were prospectively investigated. Among these, H19 (p=0.002), AGAP2-AS1 (p=0.002), and GAS5 (0.02) were significantly upregulated in patients with AVS, compared to non-AVS patients. Aortic valvular endothelial cells (VECs) were isolated from explanted valve tissue from AVS patients or obtained commercially. In vitro EndMT-promoting stimuli (TNFα or TGFß+IL1ß) were used for VEC stimulation for 5 days. RT-qPCR was used to quantify the expression of EndMT markers (EC markers, vWF, and NOS3, and mesenchymal markers, αSMA, SM22, Vimentin, and SNAI2). Loss of H19 led to dysregulation of the EC gene network and protein expression patterns that were analyzed by qRT-PCR, immunoblotting, and immunofluorescence, respectively. Further experiments show that silencing of H19 affects migration and proliferation, and promotes EndMT in EC. Functional assays suggested that H19 is a critical regulator of angiogenic properties. The molecular signature of angiogenesis was investigated using a RT-qPCR-based angiogenesis array to identify the regulation of angiogenesis with 84-angiogenesis-related genes. Mechanistically, the angiogenesis array revealed that H19 regulates Jagged Canonical Notch Ligand 1 (JAG1) (4.43-fold vs. control EC), an important regulator of NOTCH1 signaling, and pro-angiogenic factor in EC. Accordingly, EndMT marker expressions were dysregulated upon H19 depletion. A high-throughput luciferase reporter array demonstrated STAT3 activation upon H19 knockdown. Depletion of H19 increased the phosphorylation of STAT3 at TYR705 and pharmacological inhibition of STAT3 activation abolished the effects of H19 silencing on EndMT marker expression as well as on angiogenesis. Overexpression of H19 in VEC abrogated the H19-mediated promotion of JAG1- and VEGFA gene- and protein expression.

Growth differentiation factor 15 (GDF15) is elevated in human plaques and promotes endothelial-to-mesenchymal transition (EndMT)

Abstract Introduction and Purpose Growth Differentiation Factor 15 (GDF15) is a member of the TGF-β superfamily and is upregulated under conditions of injury and stress such as hypoxia. GDF15 serum concentrations correlate with inflammation, cardiac fibrosis and unfavorable prognosis in cardiovascular diseases. The functional role of GDF15 in endothelial cells is largely unknown. Here, we investigate a possible role of GDF15 in the transdifferentiation of endothelial cells (EC) into mesenchymal cells (EndMT). Methods and Results GDF15 is expressed at mRNA and protein level in primary human ECs and is secreted as determined by qPCR, single cell sequencing (scRNA-seq) and enzyme-linked immunosorbent assay (mean ± SEM, 743.8±39.3 pg/ml, n=3). Analysis of vascular sections from Ldlr-/- mice fed a high-fat diet using spatial transcriptomics revealed increased GDF15 expression. ScRNA-seq analysis of human plaques and normal vessel sections from the same individuals revealed a 22-fold ± 5.48 (p&amp;lt;0.05) increase in GDF15 in ECs located in plaques compared to ECs in control vessel regions. Experiments in cultured human endothelial cells showed increased GDF15 mRNA expression qPCR (+1.7-fold control, p&amp;lt;0.05) and scRNA-seq analysis after EndMT induction. Treatment with increasing levels of recombinant GDF15 (10, 50 and 150 ng/ml) induced EndMT as measured by expression of the EndMT marker calponin (+3.36, 7.99 and 9.53-fold, all p&amp;lt;0.05). Interestingly, EndMT induction decreased extracellular GDF15 levels (-54.6%, p&amp;lt;0.05), whereas intracellular levels in EC were increased (+1.9-fold control, p&amp;lt;0.05). The use of GDF15 neutralising antibodies (1 µg/ml) reduced soluble GDF15 levels by 97.7% as measured by ELISA (p&amp;lt;0.001). Treatment with neutralising antibodies against GDF15 reduced EndMT induction by 54% as measured by the EndMT marker calponin (p&amp;lt;0.05). Conclusion In conclusion, GDF15 is elevated in mouse and human plaques, and in EndMT. Treatment with GDF15 induces EndMT, whereas inhibition by neutralising antibodies reduces EndMT induction. These data are consistent with a functional role of GDF15 in endothelial dysfunction and atherogenesis.

HDAC9 Inhibition as a Novel Treatment for Stroke.

The identification of a variant in the HDAC9 gene as a risk factor for large-artery atherosclerotic stroke, and subsequently coronary artery disease, has opened novel treatment pathways for stroke and more widely atherosclerotic disease. This article describes the pathway from gene discovery to novel therapeutic approaches that are now entering man. HDAC9 expression is elevated in human atherosclerotic plaque, while in animal and cellular models, reducing HDAC9 (histone deacetylase 9) protein is associated with reduced disease. Several mechanisms have been proposed to account for the association between HDAC9 and atherosclerosis including alterations in the inflammatory response and cholesterol efflux and endothelial-mesenchymal transition. The association raises the possibility that inhibiting HDAC9 may provide a novel treatment approach for atherosclerotic cardiovascular disease. This is supported by intervention studies demonstrating HDAC9 inhibition reduces atherosclerosis in animal and cellular models. Indirect data support such an approach in man. The antiseizure drug sodium valproate, which has nonspecific HDAC inhibitory properties, both inhibits atherosclerosis in animal models and is epidemiologically associated with reduced stroke and myocardial infarction risk in man. It is now being trailed in phase 2 studies in large-artery stroke, while more specific HDAC9 inhibitors are being developed.

Abstract 13004: Blockade of Endothelial to Mesenchymal Transition (EndMT) by an AP-1 Inhibitor Attenuates Atherosclerosis in Diabetes

Background: Atherosclerotic cardiovascular disease is the leading cause of death in individuals with diabetes. Endothelial to mesenchymal transition (EndMT) is characterized by endothelial transformation to a mesenchymal like cellular state. EndMT-mediated endothelial cell dysfunction is known to be involved in cardiovascular complications of diabetes including atherosclerosis. Gene expression changes occur when endothelial cells transition to mesenchymal cells. These transcriptomic changes are regulated by multiple factors including transcription factors (TFs). Although, previous studies have implicated the role of EndMT in atherosclerosis, the role of AP-1 TF complex in EndMT in diabetes induced atherosclerosis is not known. Methods: Single cell transcriptomic (SCT) analysis of diabetic aorta in atheroprone Apoe -/- mice was performed using 10X Genomics platform. In vitro model mimicking diabetes-induced EndMT was established in human aortic endothelial cells (HAECs) using high glucose (25mM) and TNF- α ± a small molecular inhibitor of AP-1, T-5224. RNA and ChIP (chromatin Immunoprecipitation) sequencing was performed. Moreover, Apoe -/- mice made diabetic with streptozotocin, were treated with T-5224 (30 mg/kg daily for 5 weeks) in a 10-week intervention study. Results: SCT analysis of aorta identified increased expression of AP-1 members cFOS and Junb in diabetic endothelial cells in Apoe -/- mice. These genes were also upregulated in the HAECs-based in vitro EndMT model. Interestingly, AP-1 inhibition by T-5224 attenuated EndMT . RNA and ChIP sequencing identified several AP-1 target genes including Col1A2, Col4A1, TGFB, THBD, INSR, PIK3R3 (FDR &lt;0.05, Log2 fold change (2x)) that were common to many enriched pathways including “leukocyte trans-endothelial migration” and “AGE-RAGE signaling pathways in diabetic complications” directly relevant to EndMT in diabetes. Importantly, T-5224 treatment blocked EndMT resulting in reduced atherosclerosis in diabetic Apoe -/- mice. Conclusion: This study identified the AP-1 inhibition with T-5224 as a novel treatment for the first time for the diabetes induced EndMT and atherosclerosis.

Abstract 18853: Rescue of Pulmonary Hypertension-Induced Right Ventricular Failure by Silencing Snai1 Induces Alterations in Methylation Status of Critical Genes Regulating Endothelial-to-Mesenchymal-Transition and Fibrosis

Introduction: Pulmonary hypertension (PH)-induced RV failure (PH-RVF), a significant prognostic determinant, is characterized by RV endothelial-to-mesenchymal transition (EndMT), fibrosis, and remodeling. However, the regulatory control of RV EndMT and fibrosis remains unclear. Hypothesis: TGFβ1-Snai1-LOXL2 axis regulates RV EndMT and fibrosis in PH-RVF. Key gatekeeper transcription factor (TF) Snai1 mediates RV EndMT and fibrosis via differential methylation changes in EndMT and fibrotic genes and may serve as a novel therapeutic target. Methods: Male rats received s.c. Monocrotaline (MCT, 60mg/kg, n=9; 30-days), Sugen (20mg/kg, n=9; 3-wk hypoxia+2-wk normoxia; SuHx) or PBS (CTRL, n=9). For Snai1-knockdown (KD), MCT rats received siSnai1 (n=6; 5nM every 3-4d, IV) or scramble (n=7) from day 14-30. Echo, cath, RV-RNASeq, qPCR, WB, IF validation, and RV-DNA methylome RRBS-Seq were performed. Differentially methylated sites (DMS) and regions (DMR) were assessed. Secondary RNASeq analysis was performed on human decompensated-RVF vs Control (dRVF; GSE198618) and human RVs were assessed for EndMT, fibrosis, myofibroblast (MFB) transition, and Snai1+LOXL2. Snai1-KD was performed on human coronary artery endothelial cells (HCAECs) and human cardiac fibroblasts (HCFs) under hypoxia+TGFβ1. Results: MCT and SuHx had increased RVSP and Fulton index and decreased RVFAC (all p&lt;0.001). RNASeq showed EndMT and Snai1 as the top-upregulated pathway and TF respectively in MCT and SuHx and human dRVF. RV EndMT, fibrosis, MFB transition, TGFβ1-Snai1-LOXL2, and peri-nuclear colocalization of Snai1+LOXL2 were increased in MCT, SuHx and dRVF patients. Snai1-KD rescued PH-RVF via significantly reducing Snai1+LOXL2. RV-RNASeq demonstrated EndMT as the top-downregulated pathway and decreased fibrotic DEGs. RV RRBS-Seq showed significant DMS and DMR remodeling of Dnmt3a, Kdm1a, Snai1, TGFβ1/2, and other critical EndMT and fibrotic genes. Snai1-KD inhibited hypoxia+TGFβ1-induced EndMT in HCAEC and MFB transition in HCF by decreasing Snai1+LOXL2 expression and reversing EndMT and fibrotic DEGs respectively. Conclusions: Rescue of PH-RVF by silencing Snai1 induces alterations in methylation status of critical genes regulating EndMT and fibrosis.