Endoglin promotes transforming growth factor beta-mediated Smad 1/5/8 signaling and inhibits endothelial cell migration through its association with GIPC

Anti-Endoglin monoclonal antibody prevents the progression of liver sinusoidal endothelial inflammation and fibrosis in MASH

Liver sinusoidal endothelial inflammation/dysfunction and fibrosis are a crucial part of Metabolic Dysfunction Associated Steatohepatitis (MASH) development. TRC105 and M1043 are anti-endoglin (ENG) monoclonal antibodies that bind ENG. In this study, we hypothesized that treatment with anti-ENG antibodies would prevent the progression of LSECs inflammation and fibrosis in vivo and in vitro. MASH was induced in male C57BL/6 mice fed a choline-deficient L-amino acid-defined high-fat diet (CDAA-HFD) for 4 or 8 weeks. In the rescue study, mice were divided into three groups: a control group (chow diet), a MASH group (CDAA-HFD + IgG), and a rescue group (CDAA-HFD + M1043). Later, two groups received rat IgG1 (10 mg/kg) and M1043 (10 mg/kg). In in vitro experiments, inflammation was induced in human LSECs by ox-LDL (50 μg/mL) and treated with TRC105 (300 μg/mL). Liver sinusoidal endothelial inflammation/dysfunction in MASH animals was characterized by endothelial overexpression of ENG, VCAM-1, and ICAM-1 and reduced VE-cadherin and p-eNOS/eNOS expression. M1043 treatment prevented the overexpression of ENG, VCAM-1, and ICAM-1, the progression of liver fibrosis, and the increase of liver-to-body weight ratio. In vitro experiments with TRC105 confirmed the prevention of LSECs inflammation development by reduced ENG and VCAM-1 expression, as well as decreased THP-1 monocytic cell adhesion in ox-LDL activated LSECs. In conclusion, we demonstrate that anti-ENG antibody treatment can prevent LSECs inflammation and fibrosis progression in a MASH animal model and LSECs inflammation in vitro. Thus, we propose directly targeted ENG may represent a promising pharmacological approach for addressing LSECs inflammation and liver fibrosis.

Activins and Inhibins in Cardiovascular Pathophysiology

Activins and inhibins, members of the transforming growth factor β (TGFβ) superfamily, were initially recognized for their opposing effects on the secretion of follicle-stimulating hormone. Subsequent research has demonstrated their broader biological roles across various tissue types. Primarily, activins and inhibins function through the classical TGFβ SMAD signaling pathway, but studies suggest that they also act through other pathways, with their specific signaling being complex and context-dependent. Recent research has identified significant roles for activins and inhibins in the cardiovascular system. Their actions in other systems and their signaling pathways show strong correlations with the development and progression of cardiovascular diseases, indicating potential broader roles in the cardiovascular system. This review summarizes the progress in research on the biological functions and mechanisms of activins and inhibins and their signaling pathways in cardiovascular diseases, offering new insights for the prevention and treatment of cardiovascular diseases.

Antisense oligonucleotide-mediated terminal intron retention of endoglin: A potential strategy to inhibit renal interstitial fibrosis

TGF-β is considered an important cytokine in the development of interstitial fibrosis in chronic kidney disease. The TGF-β co-receptor endoglin (ENG) tends to be upregulated in kidney fibrosis. ENG has two membrane bound isoforms generated via alternative splicing. Long-ENG was shown to enhance the extent of renal fibrosis in an unilateral ureteral obstruction mouse model, while short-ENG inhibited renal fibrosis. Here we aimed to achieve terminal intron retention of endoglin using antisense-oligo nucleotides (ASOs), thereby shifting the ratio towards short-ENG to inhibit the TGF-β1-mediated pro-fibrotic response. We isolated mRNA from kidney biopsies of patients with chronic allograft disease (CAD) (n = 12) and measured total ENG and short-ENG mRNA levels. ENG mRNA was upregulated 2.3 fold (p < 0.05) in kidneys of CAD patients compared to controls, while the percentage short-ENG of the total ENG mRNA was significantly lower (1.8 fold; p < 0.05). Transfection of ASOs that target splicing regulatory sites of ENG into TK173 fibroblasts led to higher levels of short-ENG (2 fold; p < 0.05). In addition, we stimulated these cells with TGF-β1 and measured a decrease in upregulation of ACTA2, COL1A1 and FN1 mRNA levels, and protein expression of αSMA, collagen type I, and fibronectin. These results show a potential for ENG ASOs as a therapy to reduce interstitial fibrosis in CKD.

TEM1/endosialin/CD248 promotes pathologic scarring and TGF-β activity through its receptor stability in dermal fibroblasts

BACKGROUND

Pathologic scars, including keloids and hypertrophic scars, represent a common form of exaggerated cutaneous scarring that is difficult to prevent or treat effectively. Additionally, the pathobiology of pathologic scars remains poorly understood. We aim at investigating the impact of TEM1 (also known as endosialin or CD248), which is a glycosylated type I transmembrane protein, on development of pathologic scars.

METHODS

To investigate the expression of TEM1, we utilized immunofluorescence staining, Western blotting, and single-cell RNA-sequencing (scRNA-seq) techniques. We conducted in vitro cell culture experiments and an in vivo stretch-induced scar mouse model to study the involvement of TEM1 in TGF-β-mediated responses in pathologic scars.

RESULTS

The levels of the protein TEM1 are elevated in both hypertrophic scars and keloids in comparison to normal skin. A re-analysis of scRNA-seq datasets reveals that a major profibrotic subpopulation of keloid and hypertrophic scar fibroblasts greatly expresses TEM1, with expression increasing during fibroblast activation. TEM1 promotes activation, proliferation, and ECM production in human dermal fibroblasts by enhancing TGF-β1 signaling through binding with and stabilizing TGF-β receptors. Global deletion of Tem1 markedly reduces the amount of ECM synthesis and inflammation in a scar in a mouse model of stretch-induced pathologic scarring. The intralesional administration of ontuxizumab, a humanized IgG monoclonal antibody targeting TEM1, significantly decreased both the size and collagen density of keloids.

CONCLUSIONS

Our data indicate that TEM1 plays a role in pathologic scarring, with its synergistic effect on the TGF-β signaling contributing to dermal fibroblast activation. Targeting TEM1 may represent a novel therapeutic approach in reducing the morbidity of pathologic scars.

NRP1 interacts with endoglin and VEGFR2 to modulate VEGF signaling and endothelial cell sprouting

Endothelial cells express neuropilin 1 (NRP1), endoglin (ENG) and vascular endothelial growth factor receptor 2 (VEGFR2), which regulate VEGF-A-mediated vascular development and angiogenesis. However, the link between complex formation among these receptors with VEGF-A-induced signaling and biology is yet unclear. Here, we quantify surface receptor interactions by IgG-mediated immobilization of one receptor, and fluorescence recovery after photobleaching (FRAP) measurements of the mobility of another coexpressed receptor. We observe stable ENG/NRP1, ENG/VEGFR2, and NRP1/VEGFR2 complexes, which are enhanced by VEGF-A. ENG augments NRP1/VEGFR2 interactions, suggesting formation of tripartite complexes bridged by ENG. Effects on signaling are measured in murine embryonic endothelial cells expressing (MEEC+/+) or lacking (MEEC-/-) ENG, along with NRP1 and/or ENG overexpression or knockdown. We find that optimal VEGF-A-mediated phosphorylation of VEGFR2 and Erk1/2 requires ENG and NRP1. ENG or NRP1 increase VEGF-A-induced sprouting, becoming optimal in cells expressing all three receptors, and both processes are inhibited by a MEK1/2 inhibitor. We propose a model where the maximal potency of VEGF-A involves a tripartite complex where ENG bridges VEGFR2 and NRP1, providing an attractive therapeutic target for modulation of VEGF-A signaling and biological responses.

Human pluripotent stem cell modeling of alveolar type 2 cell dysfunction caused by ABCA3 mutations

Mutations in ATP-binding cassette A3 (ABCA3), a phospholipid transporter critical for surfactant homeostasis in pulmonary alveolar type II epithelial cells (AEC2s), are the most common genetic causes of childhood interstitial lung disease (chILD). Treatments for patients with pathological variants of ABCA3 mutations are limited, in part due to a lack of understanding of disease pathogenesis resulting from an inability to access primary AEC2s from affected children. Here, we report the generation of AEC2s from affected patient induced pluripotent stem cells (iPSCs) carrying homozygous versions of multiple ABCA3 mutations. We generated syngeneic CRISPR/Cas9 gene-corrected and uncorrected iPSCs and ABCA3-mutant knockin ABCA3:GFP fusion reporter lines for in vitro disease modeling. We observed an expected decreased capacity for surfactant secretion in ABCA3-mutant iPSC-derived AEC2s (iAEC2s), but we also found an unexpected epithelial-intrinsic aberrant phenotype in mutant iAEC2s, presenting as diminished progenitor potential, increased NFκB signaling, and the production of pro-inflammatory cytokines. The ABCA3:GFP fusion reporter permitted mutant-specific, quantifiable characterization of lamellar body size and ABCA3 protein trafficking, functional features that are perturbed depending on ABCA3 mutation type. Our disease model provides a platform for understanding ABCA3 mutation-mediated mechanisms of alveolar epithelial cell dysfunction that may trigger chILD pathogenesis.

Downregulation of stromal syntenin sustains AML development

The crosstalk between cancer and stromal cells plays a critical role in tumor progression. Syntenin is a small scaffold protein involved in the regulation of intercellular communication that is emerging as a target for cancer therapy. Here, we show that certain aggressive forms of acute myeloid leukemia (AML) reduce the expression of syntenin in bone marrow stromal cells (BMSC). Stromal syntenin deficiency, in turn, generates a pro-tumoral microenvironment. From serial transplantations in mice and co-culture experiments, we conclude that syntenin-deficient BMSC stimulate AML aggressiveness by promoting AML cell survival and protein synthesis. This pro-tumoral activity is supported by increased expression of endoglin, a classical marker of BMSC, which in trans stimulates AML translational activity. In short, our study reveals a vicious signaling loop potentially at the heart of AML-stroma crosstalk and unsuspected tumor-suppressive effects of syntenin that need to be considered during systemic targeting of syntenin in cancer therapy.

Recent advances in novel mutation genes of Parkinson's disease

With increasing life expectancy, a growing number of individuals are being affected by Parkinson's Disease (PD), a Neurodegenerative Disease (ND). Approximately, 5-10% of PD is explained by genetic causes linked to known PD genes. With improvements in genetic testing and high-throughput technologies, more PD-associated susceptibility genes have been reported in recent years. However, a comprehensive review of the pathogenic mechanisms and physiological roles of these genes is still lacking. This article reviews novel genes with putative or confirmed pathogenic mutations in PD reported since 2019, summarizes the physiological functions and potential associations with PD. Newly reported PD-related genes include ANK2, DNAH1, STAB1, NOTCH2NLC, UQCRC1, ATP10B, TFG, CHMP1A, GIPC1, KIF21B, KIF24, SLC25A39, SPTBN1 and TOMM22. However, the evidence for pathogenic effects of many of these genes is inconclusive. A variety of novel PD-associated genes have been identified through clinical cases of PD patients and analysis of Genome-Wide Association Studies (GWAS). However, more evidence is needed in confirm the strong association of novel genes with disease.

EPDR1 is a noncanonical effector of insulin-mediated angiogenesis regulated by an endothelial-specific TGF-β receptor complex

Insulin signaling in blood vessels primarily functions to stimulate angiogenesis and maintain vascular homeostasis through the canonical PI3K and MAPK signaling pathways. However, angiogenesis is a complex process coordinated by multiple other signaling events. Here, we report a distinct crosstalk between the insulin receptor and endoglin/activin receptor-like kinase 1 (ALK1), an endothelial cell-specific TGF-β receptor complex essential for angiogenesis. While the endoglin-ALK1 complex normally binds to TGF-β or bone morphogenetic protein 9 (BMP9) to promote gene regulation via transcription factors Smad1/5, we show that insulin drives insulin receptor oligomerization with endoglin-ALK1 at the cell surface to trigger rapid Smad1/5 activation. Through quantitative proteomic analysis, we identify ependymin-related protein 1 (EPDR1) as a major Smad1/5 gene target induced by insulin but not by TGF-β or BMP9. We found endothelial EPDR1 expression is minimal at the basal state but is markedly enhanced upon prolonged insulin treatment to promote cell migration and formation of capillary tubules. Conversely, we demonstrate EPDR1 depletion strongly abrogates these angiogenic effects, indicating that EPDR1 is a crucial mediator of insulin-induced angiogenesis. Taken together, these results suggest important therapeutic implications for EPDR1 and the TGF-β pathways in pathologic angiogenesis during hyperinsulinemia and insulin resistance.

Regulation of Blood-Brain Barrier Transporters by Transforming Growth Factor-β/Activin Receptor-Like Kinase 1 Signaling: Relevance to the Brain Disposition of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Inhibitors (i.e., Statins)

Our laboratory has shown that activation of transforming growth factor- β (TGF- β )/activin receptor-like kinase 1 (ALK1) signaling can increase protein expression and transport activity of organic anion transporting polypeptide 1a4 (Oatp1a4) at the blood-brain barrier (BBB). These results are relevant to treatment of ischemic stroke because Oatp transport substrates such as 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (i.e., statins) improve functional neurologic outcomes in patients. Advancement of our work requires determination if TGF- β /ALK1 signaling alters Oatp1a4 functional expression differently across brain regions and if such disparities affect central nervous system (CNS) statin disposition. Therefore, we studied regulation of Oatp1a4 by the TGF- β /ALK1 pathway, in vivo, in rat brain microvessels isolated from cerebral cortex, hippocampus, and cerebellum using the ALK1 agonist bone morphogenetic protein-9 (BMP-9) and the ALK1 inhibitor 4-[6-[4-(1-piperazinyl)phenyl]pyrazolo[1,5-a]pyrimidin-3-yl]quinoline dihydrochloride 193189. We showed that Oatp1a4 protein expression and brain distribution of three currently marketed statin drugs (i.e., atorvastatin, pravastatin, and rosuvastatin) were increased in cortex relative to hippocampus and cerebellum. Additionally, BMP-9 treatment enhanced Oatp-mediated statin transport in cortical tissue but not in hippocampus or cerebellum. Although brain drug delivery is also dependent upon efflux transporters, such as P-glycoprotein and/or Breast Cancer Resistance Protein, our data showed that administration of BMP-9 did not alter the relative contribution of these transporters to CNS disposition of statins. Overall, this study provides evidence for differential regulation of Oatp1a4 by TGF- β /ALK1 signaling across brain regions, knowledge that is critical for development of therapeutic strategies to target Oatps at the BBB for CNS drug delivery. SIGNIFICANCE STATEMENT: Organic anion transporting polypeptides (Oatps) represent transporter targets for brain drug delivery. We have shown that Oatp1a4 statin uptake is higher in cortex versus hippocampus and cerebellum. Additionally, we report that the transforming growth factor- β /activin receptor-like kinase 1 agonist bone morphogenetic protein-9 increases Oatp1a4 functional expression, but not efflux transporters P-glycoprotein and Breast Cancer Resistance Protein, in cortical brain microvessels. Overall, this study provides critical data that will advance treatment for neurological diseases where drug development has been challenging.

Fortilin interacts with TGF-β1 and prevents TGF-β receptor activation

Fortilin is a 172-amino acid multifunctional protein present in both intra- and extracellular spaces. Although fortilin binds and regulates various cellular proteins, the biological role of extracellular fortilin remains unknown. Here we report that fortilin specifically interacts with TGF-β1 and prevents it from activating the TGF-β1 signaling pathway. In a standard immunoprecipitation-western blot assay, fortilin co-immunoprecipitates TGF-β1 and its isoforms. The modified ELISA assay shows that TGF-β1 remains complexed with fortilin in human serum. Both bio-layer interferometry and surface plasmon resonance (SPR) reveal that fortilin directly bind TGF-β1. The SPR analysis also reveals that fortilin and the TGF-β receptor II (TGFβRII) compete for TGF-β1. Both luciferase and secreted alkaline phosphatase reporter assays show that fortilin prevents TGF-β1 from activating Smad3 binding to Smad-binding element. Fortilin inhibits the phosphorylation of Smad3 in both quantitative western blot assays and ELISA. Finally, fortilin inhibits TGFβ-1-induced differentiation of C3H10T1/2 mesenchymal progenitor cells to smooth muscle cells. A computer-assisted virtual docking reveals that fortilin occupies the pocket of TGF-β1 that is normally occupied by TGFβRII and that TGF-β1 can bind either fortilin or TGFβRII at any given time. These data support the role of extracellular fortilin as a negative regulator of the TGF-β1 signaling pathway.

Fortilin prevents the activation of the TGF-β1 receptor by occupying the pocket of TGF-β1 and competing with TGF-βRII to bind with TGF-β1. This inhibits Smad3 phosphorylation and the differentiation of C3H10T1/2 mesenchymal progenitor cells to smooth muscle cells.

Neurodegenerative diseases associated with non-coding CGG tandem repeat expansions

Non-coding CGG repeat expansions cause multiple neurodegenerative disorders, including fragile X-associated tremor/ataxia syndrome, neuronal intranuclear inclusion disease, oculopharyngeal myopathy with leukodystrophy, and oculopharyngodistal myopathy. The underlying genetic causes of several of these diseases have been identified only in the past 2-3 years. These expansion disorders have substantial overlapping clinical, neuroimaging and histopathological features. The shared features suggest common mechanisms that could have implications for the development of therapies for this group of diseases - similar therapeutic strategies or drugs may be effective for various neurodegenerative disorders induced by non-coding CGG expansions. In this Review, we provide an overview of clinical and pathological features of these CGG repeat expansion diseases and consider the likely pathological mechanisms, including RNA toxicity, CGG repeat-associated non-AUG-initiated translation, protein aggregation and mitochondrial impairment. We then discuss future research needed to improve the identification and diagnosis of CGG repeat expansion diseases, to improve modelling of these diseases and to understand their pathogenesis. We also consider possible therapeutic strategies. Finally, we propose that CGG repeat expansion diseases may represent manifestations of a single underlying neuromyodegenerative syndrome in which different organs are affected to different extents depending on the gene location of the repeat expansion.

G-alpha interacting protein interacting protein, C terminus 1 regulates epileptogenesis by increasing the expression of metabotropic glutamate receptor 7

Aims

It has been reported that the G‐alpha interacting protein (GAIP) interacting protein, C terminus 1 (GIPC1/GIPC) engages in vesicular trafficking, receptor transport and expression, and endocytosis. However, its role in epilepsy is unclear. Therefore, in this study, we aimed to explore the role of GIPC1 in epilepsy and its possible underlying mechanism.

Methods

The expression patterns of GIPC1 in patients with temporal lobe epilepsy (TLE) and in mice with kainic acid (KA)‐induced epilepsy were detected. Behavioral video monitoring and hippocampal local field potential (LFP) recordings were carried out to determine the role of GIPC1 in epileptogenesis after overexpression of GIPC1. Coimmunoprecipitation (Co‐IP) assay and high‐resolution immunofluorescence staining were conducted to investigate the relationship between GIPC1 and metabotropic glutamate receptor 7 (mGluR7). In addition, the expression of mGluR7 after overexpression of GIPC1 was measured, and behavioral video monitoring and LFP recordings after antagonism of mGluR7 were performed to explore the possible mechanism mediated by GIPC1.

Results

GIPC1 was downregulated in the brain tissues of patients with TLE and mice with KA‐induced epilepsy. After overexpression of GIPC1, prolonged latency period, decreased epileptic seizures and reduced seizure severity in behavioral analyses, and fewer and shorter abnormal brain discharges in LFP recordings of KA‐induced epileptic mice were observed. The result of the Co‐IP assay showed the interaction between GIPC1 and mGluR7, and the high‐resolution immunofluorescence staining also showed the colocalization of these two proteins. Additionally, along with GIPC1 overexpression, the total and cell membrane expression levels of mGluR7 were also increased. And after antagonism of mGluR7, increased epileptic seizures and aggravated seizure severity in behavioral analyses and more and longer abnormal brain discharges in LFP recordings were observed.

Conclusion

GIPC1 regulates epileptogenesis by interacting with mGluR7 and increasing its expression.

Study of expression of endoglin (CD105) in oral squamous cell carcinoma

Context:

Oral cancer is the 8^th most common cancer in the world. An important feature of carcinogenesis is angiogenesis. Endoglin is a powerful marker of neovascularization in solid malignancies. This study was done to ascertain its role as an indicator of metastasis and prognosis.

Aim:

This study aimed to evaluate and compare the expression of endoglin (CD105) in metastatic primary tumor, lymph node of the metastasized tumor, nonmetastatic primary tumor and in normal buccal mucosa immunohistochemically.

Settings and Design:

The total sample size comprised 45 formalin-fixed paraffin-embedded tissue blocks, n = 10 metastasized primary tumor, n = 10 lymph nodes of metastasized primary tumor, n = 20 nonmetastasized oral squamous cell carcinoma and n = 5 normal buccal mucosa were studied.

Subjects and Methods:

Immunohistochemistry for endoglin was performed and microvessel density (MVD) was determined by hot spot method. Microvessel density was compared between the groups.

Statistical Analysis:

Statistical analysis was used using one-way ANOVA. P < 0.05 was statistically significant.

Results:

Endoglin expression in metastatic cases (0.68 + 0.10) was higher than nonmetastatic cases (0.45 + 0.20) and the difference was statistically significant (P = 0.002).

Conclusion:

This study shows that presence of endoglin determines the metastatic potential of the tumor and its prognosis, thus, could be considered as a potential target of therapy.

A bioinformatic analysis of the inhibin-betaglycan-endoglin/CD105 network reveals prognostic value in multiple solid tumors

Inhibins and activins are dimeric ligands belonging to the TGFβ superfamily with emergent roles in cancer. Inhibins contain an α-subunit (INHA) and a β-subunit (either INHBA or INHBB), while activins are mainly homodimers of either βA (INHBA) or βB (INHBB) subunits. Inhibins are biomarkers in a subset of cancers and utilize the coreceptors betaglycan (TGFBR3) and endoglin (ENG) for physiological or pathological outcomes. Given the array of prior reports on inhibin, activin and the coreceptors in cancer, this study aims to provide a comprehensive analysis, assessing their functional prognostic potential in cancer using a bioinformatics approach. We identify cancer cell lines and cancer types most dependent and impacted, which included p53 mutated breast and ovarian cancers and lung adenocarcinomas. Moreover, INHA itself was dependent on TGFBR3 and ENG/CD105 in multiple cancer types. INHA, INHBA, TGFBR3, and ENG also predicted patients' response to anthracycline and taxane therapy in luminal A breast cancers. We also obtained a gene signature model that could accurately classify 96.7% of the cases based on outcomes. Lastly, we cross-compared gene correlations revealing INHA dependency to TGFBR3 or ENG influencing different pathways themselves. These results suggest that inhibins are particularly important in a subset of cancers depending on the coreceptor TGFBR3 and ENG and are of substantial prognostic value, thereby warranting further investigation.

Endoglin in the Spotlight to Treat Cancer

A spotlight has been shone on endoglin in recent years due to that fact of its potential to serve as both a reliable disease biomarker and a therapeutic target. Indeed, endoglin has now been assigned many roles in both physiological and pathological processes. From a molecular point of view, endoglin mainly acts as a co-receptor in the canonical TGFβ pathway, but also it may be shed and released from the membrane, giving rise to the soluble form, which also plays important roles in cell signaling. In cancer, in particular, endoglin may contribute to either an oncogenic or a non-oncogenic phenotype depending on the cell context. The fact that endoglin is expressed by neoplastic and non-neoplastic cells within the tumor microenvironment suggests new possibilities for targeted therapies. Here, we aimed to review and discuss the many roles played by endoglin in different tumor types, as well as the strong evidence provided by pre-clinical and clinical studies that supports the therapeutic targeting of endoglin as a novel clinical strategy.

ALK1 regulates the internalization of endoglin and the type III TGF-β receptor

Complex formation and endocytosis of transforming growth factor-β (TGF-β) receptors play important roles in signaling. However, their interdependence remained unexplored. Here, we demonstrate that ALK1, a TGF-β type I receptor prevalent in endothelial cells, forms stable complexes at the cell surface with endoglin and with type III TGF-β receptors (TβRIII). We show that ALK1 undergoes clathrin-mediated endocytosis (CME) faster than ALK5, type II TGF-β receptor (TβRII), endoglin, or TβRIII. These complexes regulate the endocytosis of the TGF-β receptors, with a major effect mediated by ALK1. Thus, ALK1 enhances the endocytosis of TβRIII and endoglin, while ALK5 and TβRII mildly enhance endoglin, but not TβRIII, internalization. Conversely, the slowly endocytosed endoglin has no effect on the endocytosis of either ALK1, ALK5, or TβRII, while TβRIII has a differential effect, slowing the internalization of ALK5 and TβRII, but not ALK1. Such effects may be relevant to signaling, as BMP9-mediated Smad1/5/8 phosphorylation is inhibited by CME blockade in endothelial cells. We propose a model that links TGF-β receptor oligomerization and endocytosis, based on which endocytosis signals are exposed/functional in specific receptor complexes. This has broad implications for signaling, implying that complex formation among various receptors regulates their surface levels and signaling intensities.

Strength and duration of GIPC-dependent signaling networks as determinants in cancer

GIPC is a PDZ-domain containing adaptor protein that regulates the cell surface expression and endocytic trafficking of numerous transmembrane receptors and signaling complexes. Interactions with over 50 proteins have been reported to date including VEGFR, insulin-like growth factor-1 receptor (IGF-1R), GPCRs, and APPL, many of which have essential roles in neuronal and cardiovascular development. In cancer, a major subset of GIPC-binding receptors and cytoplasmic effectors have been shown to promote tumorigenesis or metastatic progression, while other subsets have demonstrated strong tumor-suppressive effects. Given that these diverse pathways are widespread in normal tissues and human malignancies, precisely how these opposing signals are integrated and regulated within the same tumor setting likely depend on the strength and duration of their interactions with GIPC. This review highlights the major pathways and divergent mechanisms of GIPC signaling in various cancers and provide a rationale for emerging GIPC-targeted cancer therapies.

Reversine suppresses osteosarcoma cell growth through targeting BMP-Smad1/5/8-mediated angiogenesis

Reversine, or 2-(4-morpholinoanilino)-6cyclohexylaminopurine, is a 2,6-disubstituted purine derivative. This small molecule exhibits tumor-suppressive activities through different molecular mechanisms. In this study, in vitro and in vivo angiogenic models were used to elucidate the effect of Reversine on angiogenesis in the tumor suppression. Firstly, we grafted osteosarcoma-derived MNNG/HOS cell aggregates onto chick embryonic chorioallantoic membrane (CAM) to examine the vascularization of these grafts following Reversine treatment. Following culture, it was determined that Reversine inhibited MNNG/HOS grafts growth, and decreased the density of blood vessels in the chick CAM. We then used CAM and chick embryonic yolk-sac membrane (YSM) to investigate the effects of Reversine on angiogenesis. The results revealed Reversine inhibited the proliferation of endothelial cells, where cells were mainly arrested at G₁/S phase of the cell cycle. Scratch-wound assay with HUVECs revealed that Reversine suppressed cell migration in vitro. Furthermore, endothelial cells tube formation assay and chick aortic arch sprouting assay demonstrated Reversine inhibited the sprouting, migration of endothelial cells. Lastly, qPCR and western blot analyses showed BMP-associated Smad1/5/8 signaling expressions were up-regulated by Reversine treatment. Our results showed that Reversine could suppress tumor growth by inhibiting angiogenesis through BMP signaling, and suggests a potential use of Reversine as an anti-tumor therapy.

Endoglin: An 'Accessory' Receptor Regulating Blood Cell Development and Inflammation

Transforming growth factor-β1 (TGF-β1) is a pleiotropic factor sensed by most cells. It regulates a broad spectrum of cellular responses including hematopoiesis. In order to process TGF-β1-responses in time and space in an appropriate manner, there is a tight regulation of its signaling at diverse steps. The downstream signaling is mediated by type I and type II receptors and modulated by the ‘accessory’ receptor Endoglin also termed cluster of differentiation 105 (CD105). Endoglin was initially identified on pre-B leukemia cells but has received most attention due to its high expression on activated endothelial cells. In turn, Endoglin has been figured out as the causative factor for diseases associated with vascular dysfunction like hereditary hemorrhagic telangiectasia-1 (HHT-1), pre-eclampsia, and intrauterine growth restriction (IUPR). Because HHT patients often show signs of inflammation at vascular lesions, and loss of Endoglin in the myeloid lineage leads to spontaneous inflammation, it is speculated that Endoglin impacts inflammatory processes. In line, Endoglin is expressed on progenitor/precursor cells during hematopoiesis as well as on mature, differentiated cells of the innate and adaptive immune system. However, so far only pro-monocytes and macrophages have been in the focus of research, although Endoglin has been identified in many other immune system cell subsets. These findings imply a functional role of Endoglin in the maturation and function of immune cells. Aside the functional relevance of Endoglin in endothelial cells, CD105 is differentially expressed during hematopoiesis, arguing for a role of this receptor in the development of individual cell lineages. In addition, Endoglin expression is present on mature immune cells of the innate (i.e., macrophages and mast cells) and the adaptive (i.e., T-cells) immune system, further suggesting Endoglin as a factor that shapes immune responses. In this review, we summarize current knowledge on Endoglin expression and function in hematopoietic precursors and mature hematopoietic cells of different lineages.

Exploring organ-specific features of fibrogenesis using murine precision-cut tissue slices

Fibrosis is the hallmark of pathologic tissue remodelling in most chronic diseases. Despite advances in our understanding of the mechanisms of fibrosis, it remains uncured. Fibrogenic processes share conserved core cellular and molecular pathways across organs. In this study, we aimed to elucidate shared and organ-specific features of fibrosis using murine precision-cut tissue slices (PCTS) prepared from small intestine, liver and kidneys. PCTS displayed substantial differences in their baseline gene expression profiles: 70% of the extracellular matrix (ECM)-related genes were differentially expressed across the organs. Culture for 48 h induced significant changes in ECM regulation and triggered the onset of fibrogenesis in all PCTS in organ-specific manner. TGFβ signalling was activated during 48 h culture in all PCTS. However, the degree of its involvement varied: both canonical and non-canonical TGFβ pathways were activated in liver and kidney slices, while only canonical, Smad-dependent, cascade was involved in intestinal slices. The treatment with galunisertib blocked the TGFβRI/SMAD2 signalling in all PCTS, but attenuated culture-induced dysregulation of ECM homeostasis and mitigated the onset of fibrogenesis with organ-specificity. In conclusion, regardless the many common features in pathophysiology of organ fibrosis, PCTS displayed diversity in culture-induced responses and in response to the treatment with TGFβRI kinase inhibitor galunisertib, even though it targets a core fibrosis pathway. A clear understanding of the common and organ-specific features of fibrosis is the basis for developing novel antifibrotic therapies.

Endoglin Trafficking/Exosomal Targeting in Liver Cells Depends on N-Glycosylation

Injury of the liver involves a wound healing partial reaction governed by hepatic stellate cells and portal fibroblasts. Individual members of the transforming growth factor-β (TGF-β) superfamily including TGF-β itself and bone morphogenetic proteins (BMP) exert diverse and partially opposing effects on pro-fibrogenic responses. Signaling by these ligands is mediated through binding to membrane integral receptors type I/type II. Binding and the outcome of signaling is critically modulated by Endoglin (Eng), a type III co-receptor. In order to learn more about trafficking of Eng in liver cells, we investigated the membranal subdomain localization of full-length (FL)-Eng. We could show that FL-Eng is enriched in Caveolin-1-containing sucrose gradient fractions. Since lipid rafts contribute to the pool of exosomes, we could consequently demonstrate for the first time that exosomes isolated from cultured primary hepatic stellate cells and its derivatives contain Eng. Moreover, via adenoviral overexpression, we demonstrate that all liver cells have the capacity to direct Eng to exosomes, irrespectively whether they express endogenous Eng or not. Finally, we demonstrate that block of N-glycosylation does not interfere with dimerization of the receptor, but abrogates the secretion of soluble Eng (sol-Eng) and prevents exosomal targeting of FL-Eng.

CBP/p300 Drives the Differentiation of Regulatory T Cells through Transcriptional and Non-Transcriptional Mechanisms

Regulatory T cells (Treg) are immunosuppressive and negatively impact response to cancer immunotherapies. CREB-binding protein (CBP) and p300 are closely related acetyltransferases and transcriptional coactivators. Here, we evaluate the mechanisms by which CBP/p300 regulate Treg differentiation and the consequences of CBP/p300 loss-of-function mutations in follicular lymphoma. Transcriptional and epigenetic profiling identified a cascade of transcription factors essential for Treg differentiation. Mass spectrometry analysis showed that CBP/p300 acetylates prostacyclin synthase, which regulates Treg differentiation by altering proinflammatory cytokine secretion by T and B cells. Reduced Treg presence in tissues harboring CBP/p300 loss-of-function mutations was observed in follicular lymphoma. Our findings provide novel insights into the regulation of Treg differentiation by CBP/p300, with potential clinical implications on alteration of the immune landscape. SIGNIFICANCE: This study provides insights into the dynamic role of CBP/p300 in the differentiation of Tregs, with potential clinical implications in the alteration of the immune landscape in follicular lymphoma.

Synergistic Anti-Angiogenic Effects Using Peptide-Based Combinatorial Delivery of siRNAs Targeting VEGFA, VEGFR1, and Endoglin Genes

Angiogenesis is a process of new blood vessel formation, which plays a significant role in carcinogenesis and the development of diseases associated with pathological neovascularization. An important role in the regulation of angiogenesis belongs to several key pathways such as VEGF-pathways, TGF-β-pathways, and some others. Introduction of small interfering RNA (siRNA) against genes of pro-angogenic factors is a promising strategy for the therapeutic suppression of angiogenesis. These siRNA molecules need to be specifically delivered into endothelial cells, and non-viral carriers modified with cellular receptor ligands can be proposed as perspective delivery systems for anti-angiogenic therapy purposes. Here we used modular peptide carrier L1, containing a ligand for the CXCR4 receptor, for the delivery of siRNAs targeting expression of VEGFA, VEGFR1 and endoglin genes. Transfection properties of siRNA/L1 polyplexes were studied in CXCR4-positive breast cancer cells MDA-MB-231 and endothelial cells EA.Hy926. We have demonstrated the efficient down-regulation of endothelial cells migration and proliferation by anti-VEGFA, anti-VEGFR1, and anti-endoglin siRNA-induced silencing. It was found that the efficiency of anti-angiogenic treatment can be synergistically improved via the combinatorial delivery of anti-VEGFA and anti-VEGFR1 siRNAs. Thus, this approach can be useful for the development of therapeutic angiogenesis inhibition.

Identification and validation of DOCK4 as a potential biomarker for risk of bone metastasis development in patients with early breast cancer

Skeletal metastasis occurs in around 75% of advanced breast cancers, with the disease incurable once cancer cells disseminate to bone, but there remains an unmet need for biomarkers to identify patients at high risk of bone recurrence. This study aimed to identify such a biomarker and to assess its utility in predicting response to adjuvant zoledronic acid (zoledronate). We used quantitative proteomics (stable isotope labelling by amino acids in cell culture-mass spectrometry; SILAC-MS) to compare protein expression in a bone-homing variant (BM1) of the human breast cancer cell line MDA-MB-231 with parental non-bone-homing cells to identify novel biomarkers for risk of subsequent bone metastasis in early breast cancer. SILAC-MS showed that dedicator of cytokinesis protein 4 (DOCK4) was upregulated in bone-homing BM1 cells, confirmed by western blotting. BM1 cells also had enhanced invasive ability compared with parental cells, which could be reduced by DOCK4-shRNA. In a training tissue microarray (TMA) comprising 345 patients with early breast cancer, immunohistochemistry followed by Cox regression revealed that high DOCK4 expression correlated with histological grade (p = 0.004) but not oestrogen receptor status (p = 0.19) or lymph node involvement (p = 0.15). A clinical validation TMA used tissue samples and the clinical database from the large AZURE adjuvant study (n = 689). Adjusted Cox regression analyses showed that high DOCK4 expression in the control arm (no zoledronate) was significantly prognostic for first recurrence in bone (HR 2.13, 95%CI 1.06-4.30, p = 0.034). No corresponding association was found in patients who received zoledronate (HR 0.812, 95%CI 0.176-3.76, p = 0.790), suggesting that treatment with zoledronate may counteract the higher risk for bone relapse from high DOCK4-expressing tumours. High DOCK4 expression was not associated with metastasis to non-skeletal sites when these were assessed collectively. In conclusion, high DOCK4 in early breast cancer is significantly associated with aggressive disease and with future bone metastasis and is a potentially useful biomarker for subsequent bone metastasis risk. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Understanding the role of mesenchymal stem cells in urinary bladder regeneration-a preclinical study on a porcine model

BACKGROUND

The tissue engineering of urinary bladder advances rapidly reflecting clinical need for a new kind of therapeutic solution for patients requiring urinary bladder replacement. Majority of the bladder augmentation studies have been performed in small rodent or rabbit models. Insufficient number of studies examining regenerative capacity of tissue-engineered graft in urinary bladder augmentation in a large animal model does not allow for successful translation of this technology to the clinical setting. The aim of this study was to evaluate the role of adipose-derived stem cells (ADSCs) in regeneration of clinically significant urinary bladder wall defect in a large animal model.

METHODS

ADSCs isolated from a superficial abdominal Camper's fascia were labeled with PKH-26 tracking dye and subsequently seeded into bladder acellular matrix (BAM) grafts. Pigs underwent hemicystectomy followed by augmentation cystoplasty with BAM only (n = 10) or BAM seeded with autologous ADSCs (n = 10). Reconstructed bladders were subjected to macroscopic, histological, immunofluoresence, molecular, and radiological evaluations at 3 months post-augmentation.

RESULTS

Sixteen animals (n = 8 for each group) survived the 3-month follow-up without serious complications. Tissue-engineered bladder function was normal without any signs of post-voiding urine residual in bladders and in the upper urinary tracts. ADSCs enhanced regeneration of tissue-engineered urinary bladder but the process was incomplete in the central graft region. Only a small percentage of implanted ADSCs survived and differentiated into smooth muscle and endothelial cells.

CONCLUSIONS

The data demonstrate that ADSCs support regeneration of large defects of the urinary bladder wall but the process is incomplete in the central graft region. Stem cells enhance urinary bladder regeneration indirectly through paracrine effect.

Erbin plays a critical role in human umbilical vein endothelial cell migration and tubular structure formation via the Smad1/5 pathway

Angiogenesis is an important process in atherosclerosis. ErbB2 was proved to have an important role in vascular development, but it is still unclear whether Erbin expresses in vessels as well as its location and function in the vessels. In the current study, we investigated the location and function of Erbin in human umbilical veins. The human umbilical veins were prepared, and immunofluorescent analysis was performed to determine the expression of Erbin. Human umbilical vein endothelial cells (HUVECs) were cultured and the lentivirus (LV) containing Erbin RNAi was also prepared. After transfection with the lentivirus, CCK-8 assay and Annexin V-PI assay were used for cell proliferation and apoptosis, respectively. Cell migration was studied using the scratch wound healing assay and the transwell assay. The capillary-like tube formation assay was performed to illustrate the effect of Erbin on HUVEC tube formation. Expression of signaling pathway molecules was assessed with Western blot. The immunofluorescent analysis suggested that Erbin expressed in human umbilical veins and the majority of the Erbin is strongly colocalized in endothelial cells. Although knockdown of Erbin did not affect HUVEC proliferation and apoptosis, it significantly suppressed HUVEC migration and tubular structure formation. Erbin knockdown showed no effect on the ERK1/2 and Smad2/3 signaling pathways but significantly promoted Smad1/5 phosphorylation and nuclear translocation. Ablation of the Smad1/5 pathway decreased the effects of Erbin on endothelial cells. Erbin is mainly localized in endothelial cells in human umbilical veins and plays a critical role in endothelial cell migration and tubular formation via the Smad1/5 pathway.

Non-target Genes Regulate miRNAs-Mediated Migration Steering of Colorectal Carcinoma

MicroRNAs (miRNAs) trigger a two-layer regulatory network directly or through transcription factors and their co-regulators. Unlike miR-375, the role of miR-145 and miR-224 in inhibiting or driving cancer cell migration is controversial. This study is a step towards addressing the potential of miR-375, miR-145 and miR-224 expression modulation to inhibit colorectal carcinoma (CRC) cells migration in vitro through regulation of non-target genes VEGFA, TGFβ1, IGF1, CD105 and CD44. Transwell migration assay results revealed a significant subdue of migration ability of cells transfected with miR-375 and miR-145 mimics and miR-224 inhibitor. Real time PCR data showed that expression of VEGFA, TGFβ1, IGF1, CD105 and CD44 was downregulated as a consequence of exogenous re-expression of miR-375 and inhibition of miR-224. On the other hand, ectopic expression of miR-145 did not affect VEGFA, TGFβ1 and CD44 expression, while it elevated CD105 and suppressed IGF1 expression. MAP4K4, a predicted target of miR-145, was validated as a target that could play a role in miR-145-mediated regulation of migration. At mRNA level, no change was observed in expression of MAP4K4 in cells with restored expression of miR-145, while western blotting analysis revealed a 25% reduction of protein level. By applying luciferase reporter assay, a significant decrease in luciferase activity was observed, supporting that miR-145 directly target 3' UTR of MAP4K4. The study highlighted the involvement of non-target genes VEGFA, TGFβ1, IGF1, CD105 and CD44 in mediating anti- and pro-migratory effect of miR-375 and miR-224, respectively, and validated MAP4K4 as a direct target of anti-migratory miR-145.

Perinatal findings in a patient with a novel large chromosome 19p deletion

We describe the prenatal and postnatal course of an infant with a large 19p deletion. Cases such as ours will improve the knowledge of specific gene functions for every medical specialist. The goal is to allow for a more rapid diagnosis, accurate prognosis and to decrease the likelihood of complications.

Endoglin Expression on Cancer-Associated Fibroblasts Regulates Invasion and Stimulates Colorectal Cancer Metastasis

PURPOSE

Cancer-associated fibroblasts (CAF) are a major component of the colorectal cancer tumor microenvironment. CAFs play an important role in tumor progression and metastasis, partly through TGF-β signaling pathway. We investigated whether the TGF-β family coreceptor endoglin is involved in CAF-mediated invasion and metastasis.

EXPERIMENTAL DESIGN

CAF-specific endoglin expression was studied in colorectal cancer resection specimens using IHC and related to metastases-free survival. Endoglin-mediated invasion was assessed in vitro by transwell invasion, using primary colorectal cancer-derived CAFs. Effects of CAF-specific endoglin expression on tumor cell invasion were investigated in a colorectal cancer zebrafish model, whereas liver metastases were assessed in a mouse model.

RESULTS

CAFs specifically at invasive borders of colorectal cancer express endoglin and increased expression intensity correlated with increased disease stage. Endoglin-expressing CAFs were also detected in lymph node and liver metastases, suggesting a role in colorectal cancer metastasis formation. In stage II colorectal cancer, CAF-specific endoglin expression at invasive borders correlated with poor metastasis-free survival. In vitro experiments revealed that endoglin is indispensable for bone morphogenetic protein (BMP)-9-induced signaling and CAF survival. Targeting endoglin using the neutralizing antibody TRC105 inhibited CAF invasion in vitro. In zebrafish, endoglin-expressing fibroblasts enhanced colorectal tumor cell infiltration into the liver and decreased survival. Finally, CAF-specific endoglin targeting with TRC105 decreased metastatic spread of colorectal cancer cells to the mouse liver.

CONCLUSIONS

Endoglin-expressing CAFs contribute to colorectal cancer progression and metastasis. TRC105 treatment inhibits CAF invasion and tumor metastasis, indicating an additional target beyond the angiogenic endothelium, possibly contributing to beneficial effects reported during clinical evaluations.See related commentary by Becker and LeBleu, p. 6110.

Identification of Sex-associated SNPs of Greater Amberjack (Seriola dumerili)

The sex determination systems of fish are highly diverse compared with those of mammals. Thus, performing investigations using nonmodel fish species helps to understand the highly diverse sex determination systems of fish. Because greater amberjack (Seriola dumerili) is one of the most important edible fish globally and knowledge of its sex determination system is economically important in the field of aquaculture, we are interested in the mechanisms of sex determination of Seriola species. In this study, we identified sex-associated SNPs of greater amberjack using SNP information of 10 males and 10 females by an association test. We determined that the sex-associated SNPs were on chromosome 12 and mainly covered with two scaffolds (about 7.1 Mbp). Genotypes of sex-associated SNPs indicated that females are the heterogametic sex (ZZ/ZW). Furthermore, we compared the genomic structure of greater amberjack with those of Japanese amberjack (Seriola quinqueradiata), California yellowtail (Seriola dorsalis), and medaka (Oryzias latipes). Whole-genome alignments and synteny analysis indicated that the sex determination system of greater amberjack is markedly different from that of medaka and implied that the sex determination system is conserved in the Seriola species.

Antagonizing CD105 enhances radiation sensitivity in prostate cancer

Radiation therapy is the primary intervention for nearly half of the patients with localized advanced prostate cancer and standard of care for recurrent disease following surgery. The development of radiation-resistant disease is an obstacle for nearly 30–50% of patients undergoing radiotherapy. A better understanding of mechanisms that lead to radiation resistance could aid in the development of sensitizing agents to improve outcome. Here we identified a radiation-resistance pathway mediated by CD105, downstream of BMP and TGF-β signaling. Antagonizing CD105-dependent BMP signaling with a partially humanized monoclonal antibody, TRC105, resulted in a significant reduction in clonogenicity when combined with irradiation. In trying to better understand the mechanism for the radio-sensitization, we found that radiation-induced CD105/BMP signaling was sufficient and necessary for the upregulation of sirtuin 1 (SIRT1) in contributing to p53 stabilization and PGC-1α activation. Combining TRC105 with irradiation delayed DNA damage repair compared to irradiation alone. However, in the absence of p53 function, combining TRC105 and radiation resulted in no reduction in clonogenicity compared to radiation alone, despite similar reduction of DNA damage repair observed in p53-intact cells. This suggested DNA damage repair was not the sole determinant of CD105 radio-resistance. As cancer cells undergo an energy deficit following irradiation, due to the demands of DNA and organelle repair, we examined SIRT1’s role on p53 and PGC-1α with respect to glycolysis and mitochondrial biogenesis, respectively. Consequently, blocking the CD105-SIRT1 axis was found to deplete the ATP stores of irradiated cells and cause G2 cell cycle arrest. Xenograft models supported these findings that combining TRC105 with irradiation significantly reduces tumor size over irradiation alone (p value = 10⁻⁹). We identified a novel synthetic lethality strategy of combining radiation and CD105 targeting to address the DNA repair and metabolic addiction induced by irradiation in p53-functional prostate cancers.

Human genetics and molecular mechanisms of vein of Galen malformation

Vein of Galen malformations (VOGMs) are rare developmental cerebrovascular lesions characterized by fistulas between the choroidal circulation and the median prosencephalic vein. Although the treatment of VOGMs has greatly benefited from advances in endovascular therapy, including technical innovation in interventional neuroradiology, many patients are recalcitrant to procedural intervention or lack accessibility to specialized care centers, highlighting the need for improved screening, diagnostics, and therapeutics. A fundamental obstacle to identifying novel targets is the limited understanding of VOGM molecular pathophysiology, including its human genetics, and the lack of an adequate VOGM animal model. Herein, the known human mutations associated with VOGMs are reviewed to provide a framework for future gene discovery. Gene mutations have been identified in 2 Mendelian syndromes of which VOGM is an infrequent but associated phenotype: capillary malformation-arteriovenous malformation syndrome ( RASA1) and hereditary hemorrhagic telangiectasia ( ENG and ACVRL1). However, these mutations probably represent only a small fraction of all VOGM cases. Traditional genetic approaches have been limited in their ability to identify additional causative genes for VOGM because kindreds are rare, limited in patient number, and/or seem to have sporadic inheritance patterns, attributable in part to incomplete penetrance and phenotypic variability. The authors hypothesize that the apparent sporadic occurrence of VOGM may frequently be attributable to de novo mutation or incomplete penetrance of rare transmitted variants. Collaboration among treating physicians, patients' families, and investigators using next-generation sequencing could lead to the discovery of novel genes for VOGM. This could improve the understanding of normal vascular biology, elucidate the pathogenesis of VOGM and possibly other more common arteriovenous malformation subtypes, and pave the way for advances in the diagnosis and treatment of patients with VOGM.

Bone Morphogenetic Proteins in Vascular Homeostasis and Disease

It is well established that control of vascular morphogenesis and homeostasis is regulated by vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), Delta-like 4 (Dll4), angiopoietin, and ephrin signaling. It has become clear that signaling by bone morphogenetic proteins (BMPs), which have a long history of studies in bone and early heart development, are also essential for regulating vascular function. Indeed, mutations that cause deregulated BMP signaling are linked to two human vascular diseases, hereditary hemorrhagic telangiectasia and pulmonary arterial hypertension. These observations are corroborated by data obtained with vascular cells in cell culture and in mouse models. BMPs are required for normal endothelial cell differentiation and for venous/arterial and lymphatic specification. In adult life, BMP signaling orchestrates neo-angiogenesis as well as vascular inflammation, remodeling, and calcification responses to shear and oxidative stress. This review emphasizes the pivotal role of BMPs in the vascular system, based on studies of mouse models and human vascular disorders.

Hepatitis C Virus Core Protein Modulates Endoglin (CD105) Signaling Pathway for Liver Pathogenesis

Endoglin is part of the TGF-β receptor complex and has a crucial role in fibrogenesis and angiogenesis. It is also an important protein for tumor growth, survival, and cancer cell metastasis. In a previous study, we have shown that hepatitis C virus (HCV) infection induces epithelial-mesenchymal transition (EMT) state and cancer stem-like cell (CSC) properties in human hepatocytes. Our array data suggested that endoglin (CD105) mRNA is significantly upregulated in HCV-associated CSCs. In this study, we have observed increased endoglin expression on the cell surface of an HCV core-expressing hepatocellular carcinoma (HepG2) cell line or immortalized human hepatocytes (IHH) and activation of its downstream signaling molecules. The status of phospho-SMAD1/5 and the expression of inhibitor of DNA binding protein 1 (ID1) were upregulated in HCV-infected cells or viral core gene-transfected cells. Additionally, we observed upregulation of endoglin/ID1 mRNA expression in chronic HCV patient liver biopsy samples. CSC generation by HCV core protein was dependent on the endoglin signaling pathway using activin receptor-like kinase 1 (ALK1) Fc blocking peptide and endoglin small interfering RNA (siRNA). Further, follow-up from in vitro analysis suggested that the antiapoptosis Bcl2 protein, proliferation-related cyclin D1 protein, and CSC-associated Hes1, Notch1, Nanog, and Sox2 proteins are enhanced during infection or ectopic expression of HCV core protein.IMPORTANCE Endoglin plays a crucial role in fibrogenesis and angiogenesis and is an important protein for tumor growth, survival, and cancer cell metastasis. Endoglin enhances ALK1-SMAD1/5 signaling in different cell types, leading to increased proliferation and migration responses. We have observed endoglin expression on the HCV core-expressing cell surface of human hepatocyte origin and activation of phospho-SMAD1/5 and ID1 downstream signaling molecules. ID1 protein plays a role in CSC properties, and we found that this pathway is important for antiapoptotic and cell proliferation signaling. Blocking of endoglin-ALK1-SMAD1/5 might be a good candidate for therapy for liver cancer stem cells together with liver cirrhosis.

Endoglin Mediates Vascular Maturation by Promoting Vascular Smooth Muscle Cell Migration and Spreading

Supplemental Digital Content is available in the text.

Objective—

Endoglin, a transforming growth factor-β superfamily coreceptor, is predominantly expressed in endothelial cells and has essential roles in vascular development. However, whether endoglin is also expressed in vascular smooth muscle cells (VSMCs), especially in vivo, remains controversial. Furthermore, the roles of endoglin in VSMC biology remain largely unknown. Our objective was to examine the expression and determine the function of endoglin in VSMCs during angiogenesis.

Approach and Results—

Here, we determine that endoglin is robustly expressed in VSMCs. Using CRISPR/CAS9 knockout and short hairpin RNA knockdown in the VSMC/endothelial coculture model system, we determine that endoglin in VSMCs, but not in endothelial cells, promotes VSMCs recruitment by the endothelial cells both in vitro and in vivo. Using an unbiased bioinformatics analysis of RNA sequencing data and further study, we determine that, mechanistically, endoglin mediates VSMC recruitment by promoting VSMC migration and spreading on endothelial cells via increasing integrin/FAK pathway signaling, whereas endoglin has minimal effects on VSMC adhesion to endothelial cells. In addition, we further determine that loss of endoglin in VSMCs inhibits VSMC recruitment in vivo.

Conclusions—

These studies demonstrate that endoglin has an important role in VSMC recruitment and blood vessel maturation during angiogenesis and also provide novel insights into how discordant endoglin function in endothelial and VSMCs may regulate vascular maturation and angiogenesis.

Overexpression of CD109 in the Epidermis Differentially Regulates ALK1 Versus ALK5 Signaling and Modulates Extracellular Matrix Synthesis in the Skin

Transforming growth factor-β (TGF-β) is a multifunctional growth factor involved in many physiological processes including wound healing and inflammation. Excessive TGF-β signaling in the skin has been implicated in fibrotic skin disorders such as keloids and scleroderma. We previously identified CD109 as a TGF-β co-receptor and inhibitor of TGF-β signaling and have shown that transgenic mice overexpressing CD109 in the epidermis display decreased scarring. In certain cell types, in addition to the canonical type I receptor, ALK5, which activates Smad2/3, TGF-β can signal through another type I receptor, ALK1, which activates Smad1/5. Here we demonstrate that ALK1 is expressed and co-localizes with CD109 in mouse keratinocytes and that mice overexpressing CD109 in the epidermis display enhanced ALK1-Smad1/5 signaling but decreased ALK5-Smad2/3 signaling, TGF-β expression, and extracellular matrix production in the skin when compared with wild-type littermates. Furthermore, treatment with conditioned media from isolated keratinocytes or epidermal explants from CD109 transgenic mouse skin leads to a decrease in extracellular matrix production in mouse skin fibroblasts. Taken together, our findings suggest that CD109 differentially regulates TGF-β-induced ALK1-Smad1/5 versus ALK5-Smad2/3 pathways, leading to decreased extracellular matrix production in the skin and that epidermal CD109 expression regulates dermal function through a paracrine mechanism.

Signaling Receptors for TGF-β Family Members

Transforming growth factor β (TGF-β) family members signal via heterotetrameric complexes of type I and type II dual specificity kinase receptors. The activation and stability of the receptors are controlled by posttranslational modifications, such as phosphorylation, ubiquitylation, sumoylation, and neddylation, as well as by interaction with other proteins at the cell surface and in the cytoplasm. Activation of TGF-β receptors induces signaling via formation of Smad complexes that are translocated to the nucleus where they act as transcription factors, as well as via non-Smad pathways, including the Erk1/2, JNK and p38 MAP kinase pathways, and the Src tyrosine kinase, phosphatidylinositol 3'-kinase, and Rho GTPases.

Tendon progenitor cells in injured tendons have strong chondrogenic potential: the CD105-negative subpopulation induces chondrogenic degeneration

To study the cellular mechanism of the tendon repair process, we used a mouse Achilles tendon injury model to focus on the cells recruited to the injured site. The cells isolated from injured tendon 1 week after the surgery and uninjured tendons contained the connective tissue progenitor populations as determined by colony-forming capacity, cell surface markers, and multipotency. When the injured tendon-derived progenitor cells (inTPCs) were transplanted into injured Achilles tendons, they were not only integrated in the regenerating area expressing tenogenic phenotype but also trans-differentiated into chondrogenic cells in the degenerative lesion that underwent ectopic endochondral ossification. Surprisingly, the micromass culture of the inTPCs rapidly underwent chondrogenic differentiation even in the absence of exogenous bone morphogenetic proteins or TGFβs. The cells isolated from human ruptured tendon tissues also showed connective tissue progenitor properties and exhibited stronger chondrogenic ability than bone marrow stromal cells. The mouse inTPCs contained two subpopulations one positive and one negative for CD105, a coreceptor of the TGFβ superfamily. The CD105-negative cells showed superior chondrogenic potential in vitro and induced larger chondroid degenerative lesions in mice as compared to the CD105-positive cells. These findings indicate that tendon progenitor cells are recruited to the injured site of tendons and have a strong chondrogenic potential and that the CD105-negative population of these cells would be the cause for chondroid degeneration in injured tendons. The newly identified cells recruited to the injured tendon may provide novel targets to develop therapeutic strategies to facilitate tendon repair.

Identification of Sex-Linked SNPs and Sex-Determining Regions in the Yellowtail Genome

Unlike the conservation of sex-determining (SD) modes seen in most mammals and birds, teleost fishes exhibit a wide variety of SD systems and genes. Hence, the study of SD genes and sex chromosome turnover in fish is one of the most interesting topics in evolutionary biology. To increase resolution of the SD gene evolutionary trajectory in fish, identification of the SD gene in more fish species is necessary. In this study, we focused on the yellowtail, a species widely cultivated in Japan. It is a member of family Carangidae in which no heteromorphic sex chromosome has been observed, and no SD gene has been identified to date. By performing linkage analysis and BAC walking, we identified a genomic region and SNPs with complete linkage to yellowtail sex. Comparative genome analysis revealed the yellowtail SD region ancestral chromosome structure as medaka-fugu. Two inversions occurred in the yellowtail linage after it diverged from the yellowtail-medaka ancestor. An association study using wild yellowtails and the SNPs developed from BAC ends identified two SNPs that can reasonably distinguish the sexes. Therefore, these will be useful genetic markers for yellowtail breeding. Based on a comparative study, it was suggested that a PDZ domain containing the GIPC protein might be involved in yellowtail sex determination. The homomorphic sex chromosomes widely observed in the Carangidae suggest that this family could be a suitable marine fish model to investigate the early stages of sex chromosome evolution, for which our results provide a good starting point.

ADAM17 Promotes Motility, Invasion, and Sprouting of Lymphatic Endothelial Cells

Tumor-associated lymphatic vessels actively participate in tumor progression and dissemination. ADAM17, a sheddase for numerous growth factors, cytokines, receptors, and cell adhesion molecules, is believed to promote tumor development, facilitating both tumor cell proliferation and migration, as well as tumor angiogenesis. In this work we addressed the issue of whether ADAM17 may also promote tumor lymphangiogenesis. First, we found that ADAM17 is important for the migratory potential of immortalized human dermal lymphatic endothelial cells (LEC). When ADAM17 was stably silenced in LEC, their proliferation was not affected, but: (i) single-cell motility, (ii) cell migration through a 3D Matrigel/collagen type I matrix, and (iii) their ability to form sprouts in a 3D matrix were significantly diminished. The differences in the cell motility between ADAM17-proficient and ADAM17-silenced cells were eliminated by inhibitors of EGFR and HER2, indicating that ADAM17-mediated shedding of growth factors accounts for LEC migratory potential. Interestingly, ADAM17 depletion affected the integrin surface expression/functionality in LEC. ADAM17-silenced cells adhered to plastic, type I collagen, and fibronectin faster than their ADAM17-proficient counterparts. The difference in adhesion to fibronectin was abolished by a cyclic RGD peptide, emphasizing the involvement of integrins in the process. Using a soluble receptor array, we identified BIG-H3 among several candidate proteins involved in the phenotypic and behavioral changes of LEC upon ADAM17 silencing. In additional assays, we confirmed the increased expression of BIG-H3, as well as TGFβ2 in ADAM17-silenced LEC. The antilymphangiogenic effects of ADAM17 silencing in lymphatic endothelial cells suggest further relevance of ADAM17 as a potential target in cancer therapy.

VEGF, Notch and TGFβ/BMPs in regulation of sprouting angiogenesis and vascular patterning

The blood vasculature is constantly adapting to meet the demand from tissue. In so doing, branches may form, reorganize or regress. These complex processes employ integration of multiple signalling cascades, some of them being restricted to endothelial and mural cells and, hence, suitable for targeting of the vasculature. Both genetic and drug targeting experiments have demonstrated the requirement for the vascular endothelial growth factor (VEGF) system, the Delta-like-Notch system and the transforming growth factor β (TGFβ)/bone morphogenetic protein (BMP) cascades in vascular development. Although several of these signalling cascades in part converge into common downstream components, they differ in temporal and spatial regulation and expression. For example, the pro-angiogenic VEGFA is secreted by cells in need of oxygen, presented to the basal side of the endothelium, whereas BMP9 and BMP10 are supplied via the bloodstream in constant interaction with the apical side to suppress angiogenesis. Delta-like 4 (DLL4), on the other hand, is provided as an endothelial membrane bound ligand. In the present article, we discuss recent data on the integration of these pathways in the process of sprouting angiogenesis and vascular patterning and malformation.

Regulation of TGF-β receptor hetero-oligomerization and signaling by endoglin

Endoglin is a modulator of TGF-β signaling in endothelial cells. We show that it forms stable homodimers serving as a scaffold for binding TβRII, ALK5, and ALK1. ALK1 and ALK5 bind endoglin differentially, with TβRII recruiting ALK5. Signaling data indicate a role for this receptor complex in balancing TGF-β signaling between Smad1/5/8 and Smad2/3.

Complex formation among transforming growth factor-β (TGF-β) receptors and its modulation by coreceptors represent an important level of regulation for TGF-β signaling. Oligomerization of ALK5 and the type II TGF-β receptor (TβRII) has been thoroughly investigated, both in vitro and in intact cells. However, such studies, especially in live cells, are missing for the endothelial cell coreceptor endoglin and for the ALK1 type I receptor, which enables endothelial cells to respond to TGF-β by activation of both Smad2/3 and Smad1/5/8. Here we combined immunoglobulin G–mediated immobilization of one cell-surface receptor with lateral mobility studies of a coexpressed receptor by fluorescence recovery after photobleaching (FRAP) to demonstrate that endoglin forms stable homodimers that function as a scaffold for binding TβRII, ALK5, and ALK1. ALK1 and ALK5 bind to endoglin with differential dependence on TβRII, which plays a major role in recruiting ALK5 to the complex. Signaling data indicate a role for the quaternary receptor complex in regulating the balance between TGF-β signaling to Smad1/5/8 and to Smad2/3.

Increased endothelial cell permeability in endoglin-deficient cells

Endoglin (ENG) is a TGF-β superfamily coreceptor essential for vascular endothelium integrity. ENG mutations lead to a vascular dysplasia associated with frequent hemorrhages in multiple organs, whereas ENG null mouse embryos die at midgestation with impaired heart development and leaky vasculature. ENG interacts with several proteins involved in cell adhesion, and we postulated that it regulates vascular permeability. The current study assessed the permeability of ENG homozygous null (Eng(-/-)), heterozygous (Eng(+/-)), and normal (Eng(+/+)) mouse embryonic endothelial cell (EC) lines. Permeability, measured by passage of fluorescent dextran through EC monolayers, was increased 2.9- and 1.7-fold for Eng(-/-) and Eng(+/-) ECs, respectively, compared to control ECs and was not increased by TGF-β1 or VEGF. Prolonged starvation increased Eng(-/-) EC permeability by 3.7-fold with no effect on control ECs; neutrophils transmigrated faster through Eng(-/-) than Eng(+/+) monolayers. Using a pull-down assay, we demonstrate that Ras homolog gene family (Rho) A is constitutively active in Eng(-/-) and Eng(+/-) ECs. We show that the endothelial barrier destabilizing factor thrombospondin-1 and its receptor-like protein tyrosine phosphatase are increased, whereas stabilizing factors VEGF receptor 2, vascular endothelial-cadherin, p21-activated kinase, and Ras-related C3 botulinum toxin substrate 2 are decreased in Eng(-/-) cells. Our findings indicate that ENG deficiency leads to EC hyperpermeability through constitutive activation of RhoA and destabilization of endothelial barrier function.

The balance of cell surface and soluble type III TGF-β receptor regulates BMP signaling in normal and cancerous mammary epithelial cells

Bone morphogenetic proteins (BMPs) are members of the TGF-β superfamily that are over-expressed in breast cancer, with context dependent effects on breast cancer pathogenesis. The type III TGF-β receptor (TβRIII) mediates BMP signaling. While TβRIII expression is lost during breast cancer progression, the role of TβRIII in regulating BMP signaling in normal mammary epithelium and breast cancer cells has not been examined. Restoring TβRIII expression in a 4T1 murine syngeneic model of breast cancer suppressed Smad1/5/8 phosphorylation and inhibited the expression of the BMP transcriptional targets, Id1 and Smad6, in vivo. Similarly, restoring TβRIII expression in human breast cancer cell lines or treatment with sTβRIII inhibited BMP-induced Smad1/5/8 phosphorylation and BMP-stimulated migration and invasion. In normal mammary epithelial cells, shRNA-mediated silencing of TβRIII, TβRIII over-expression, or treatment with sTβRIII inhibited BMP-mediated phosphorylation of Smad1/5/8 and BMP induced migration. Inhibition of TβRIII shedding through treatment with TAPI-2 or expression of a non-shedding TβRIII mutant rescued TβRIII mediated inhibition of BMP induced Smad1/5/8 phosphorylation and BMP induced migration and/or invasion in both in normal mammary epithelial cells and breast cancer cells. Conversely, expression of a TβRIII mutant, which exhibited increased shedding, significantly reduced BMP-mediated Smad1/5/8 phosphorylation, migration, and invasion. These data demonstrate that TβRIII regulates BMP-mediated signaling and biological effects, primarily through the ligand sequestration effects of sTβRIII in normal and cancerous mammary epithelial cells and suggest that the ratio of membrane bound versus sTβRIII plays an important role in mediating these effects.

The role of endoglin in kidney fibrosis

Tubulointerstitial fibrosis and glomerulosclerosis, are a major feature of end stage chronic kidney disease (CKD), characterised by an excessive accumulation of extracellular matrix (ECM) proteins. Transforming growth factor beta-1 (TGF-β1) is a cytokine with an important role in many steps of renal fibrosis such as myofibroblast activation and proliferation, ECM protein synthesis and inflammatory cell infiltration. Endoglin is a TGF-β co-receptor that modulates TGF-β responses in different cell types. In numerous cells types, such as mesangial cells or myoblasts, endoglin regulates negatively TGF-β-induced ECM protein expression. However, recently it has been demonstrated that 'in vivo' endoglin promotes fibrotic responses. Furthermore, several studies have demonstrated an increase of endoglin expression in experimental models of renal fibrosis in the kidney and other tissues. Nevertheless, the role of endoglin in renal fibrosis development is unclear and a question arises: Does endoglin protect against renal fibrosis or promotes its development? The purpose of this review is to critically analyse the recent knowledge relating to endoglin and renal fibrosis. Knowledge of endoglin role in this pathology is necessary to consider endoglin as a possible therapeutic target against renal fibrosis.

Inhibition of endoglin-GIPC interaction inhibits pancreatic cancer cell growth

Endoglin, a 180-kDa disulfide-linked homodimeric transmembrane receptor protein mostly expressed in tumor-associated endothelial cells, is an endogenous binding partner of GAIP-interacting protein, C terminus (GIPC). Endoglin functions as a coreceptor of TβRII that binds TGFβ and is important for vascular development, and consequently has become a compelling target for antiangiogenic therapies. A few recent studies in gastrointestinal stromal tumor (GIST), breast cancer, and ovarian cancer, however, suggest that endoglin is upregulated in tumor cells and is associated with poor prognosis. These findings indicate a broader role of endoglin in tumor biology, beyond angiogenic effects. The goal of our current study is to evaluate the effects of targeting endoglin in pancreatic cancer both in vitro and in vivo. We analyzed the antiproliferative effect of both RNAi-based and peptide ligand-based inhibition of endoglin in pancreatic cancer cell lines, the latter yielding a GIPC PDZ domain-targeting lipopeptide with notable antiproliferative activity. We further demonstrated that endoglin inhibition induced a differentiation phenotype in the pancreatic cancer cells and sensitized them against conventional chemotherapeutic drug gemcitabine. Most importantly, we have demonstrated the antitumor effect of both RNAi-based and competitive inhibitor-based blocking of endoglin in pancreatic cancer xenograft models in vivo. To our knowledge, this is the first report exploring the effect of targeting endoglin in pancreatic cancer cells.

Investigation of endoglin wild-type and missense mutant protein heterodimerisation using fluorescence microscopy based IF, BiFC and FRET analyses

The homodimeric transmembrane receptor endoglin (CD105) plays an important role in angiogenesis. This is highlighted by mutations in its gene, causing the vascular disorder HHT1. The main role of endoglin function has been assigned to the modulation of transforming growth factor β and bone morphogenetic protein signalling in endothelial cells. Nevertheless, other functions of endoglin have been revealed to be involved in different cellular functions and in other cell types than endothelial cells. Compared to the exploration of its natural function, little experimental data have been gathered about the mode of action of endoglin HHT mutations at the cellular level, especially missense mutations, and to what degree these might interfere with normal endoglin function. In this paper, we have used fluorescence-based microscopic techniques, such as bimolecular fluorescence complementation (BiFC), immunofluorescence staining with the endoglin specific monoclonal antibody SN6, and protein interaction studies by Förster Resonance Energy Transfer (FRET) to investigate the formation and cellular localisation of possible homo- and heterodimers composed of endoglin wild-type and endoglin missense mutant proteins. The results show that all of the investigated missense mutants dimerise with themselves, as well as with wild-type endoglin, and localise, depending on the position of the affected amino acid, either in the rough endoplasmic reticulum (rER) or in the plasma membrane of the cells. We show that the rER retained mutants reduce the amount of endogenous wild-type endoglin on the plasma membrane through interception in the rER when transiently or stably expressed in HMEC-1 endothelial cells. As a result of this, endoglin modulated TGF-β1 signal transduction is also abrogated, which is not due to TGF-β receptor ER trafficking interference. Protein interaction analyses by FRET show that rER located endoglin missense mutants do not perturb protein processing of other membrane receptors, such as TβRII, ALK5 or ALK1.