New insight into ischemic stroke: Circadian rhythm in post-stroke angiogenesis

The circadian rhythm is an endogenous clock system that coordinates and optimizes various physiological and pathophysiological processes, which accord with the master and the peripheral clock. Increasing evidence indicates that endogenous circadian rhythm disruption is involved in the lesion volume and recovery of ischemic stroke. As a critical recovery mechanism in post-stroke, angiogenesis reestablishes the regional blood supply and enhances cognitive and behavioral abilities, which is mainly composed of the following processes: endothelial cell proliferation, migration, and pericyte recruitment. The available evidence revealed that the circadian governs many aspects of angiogenesis. This study reviews the mechanism by which circadian rhythms regulate the process of angiogenesis and its contribution to functional recovery in post-stroke at the aspects of the molecular level. A comprehensive understanding of the circadian clock regulating angiogenesis in post-stroke is expected to develop new strategies for the treatment of cerebral infarction.

Dynamic changes in endoglin expression in the developing mouse heart

Endoglin (ENG) is essential for cardiovascular development and is expressed in the heart from its earliest developmental stages. ENG expression has been reported in the cardiac crescent, endocardium, valve mesenchyme and coronary vascular endothelial cells. However, its expression in these cell types is non-uniform and the dynamic changes in ENG expression during heart development have not been systematically studied. Using immunofluorescent staining we tracked ENG protein expression in mouse embryonic hearts aged from 11.5 to 17.5 days, and in postnatal and adult hearts. ENG is expressed in the endocardium and in venous endothelial cells throughout these developmental stages. ENG protein is down-regulated by approximately two-fold as a subset of early coronary veins reprogram to form arteries within the developing myocardium from E13.5. This two-fold higher ratio of ENG protein in veins versus arteries is maintained throughout cardiac development and in the adult heart. ENG is also down-regulated two-fold following mesenchymal transition of endocardial cells to form cardiac valve mesenchyme, whilst expression of the pan-endothelial marker CD31 is completely lost. A subset of epicardial cells (which do not express ENG protein) delaminate and undergo a similar mesenchymal transition to form epicardially derived cells (EPDCs). This transient intra-myocardial mesenchymal cell population expresses low levels of ENG protein, similar to valve mesenchyme. In conclusion, ENG shows dynamic changes of expression in vascular endothelial cells, endocardial cells and mesenchymal cells in the developing heart that vary according to cardiovascular cell type.

Decorin expression is associated with predictive diffusion MR phenotypes of anti-VEGF efficacy in glioblastoma

Previous data suggest that apparent diffusion coefficient (ADC) imaging phenotypes predict survival response to anti-VEGF monotherapy in glioblastoma. However, the mechanism by which imaging may predict clinical response is unknown. We hypothesize that decorin (DCN), a proteoglycan implicated in the modulation of the extracellular microenvironment and sequestration of pro-angiogenic signaling, may connect ADC phenotypes to survival benefit to anti-VEGF therapy. Patients undergoing resection for glioblastoma as well as patients included in The Cancer Genome Atlas (TCGA) and IVY Glioblastoma Atlas Project (IVY GAP) databases had pre-operative imaging analyzed to calculate pre-operative ADC_L values, the average ADC in the lower distribution using a double Gaussian mixed model. ADC_L values were correlated to available RNA expression from these databases as well as from RNA sequencing from patient derived mouse orthotopic xenograft samples. Targeted biopsies were selected based on ADC values and prospectively collected during resection. Surgical specimens were used to evaluate for DCN RNA and protein expression by ADC value. The IVY Glioblastoma Atlas Project Database was used to evaluate DCN localization and relationship with VEGF pathway via in situ hybridization maps and RNA sequencing data. In a cohort of 35 patients with pre-operative ADC imaging and surgical specimens, DCN RNA expression levels were significantly larger in high ADC_L tumors (41.6 vs. 1.5; P = 0.0081). In a cohort of 17 patients with prospectively targeted biopsies there was a positive linear correlation between ADC_L levels and DCN protein expression between tumors (Pearson R² = 0.3977; P = 0.0066) and when evaluating different targets within the same tumor (Pearson R² = 0.3068; P = 0.0139). In situ hybridization data localized DCN expression to areas of microvascular proliferation and immunohistochemical studies localized DCN protein expression to the tunica adventitia of blood vessels within the tumor. DCN expression positively correlated with VEGFR1 & 2 expression and localized to similar areas of tumor. Increased ADC_L on diffusion MR imaging is associated with high DCN expression as well as increased survival with anti-VEGF therapy in glioblastoma. DCN may play an important role linking the imaging features on diffusion MR and anti-VEGF treatment efficacy. DCN may serve as a target for further investigation and modulation of anti-angiogenic therapy in GBM.

TGF-β Signaling: A Therapeutic Target to Reinstate Regenerative Plasticity in Vascular Dementia?

Vascular dementia (VaD) is the second leading form of memory loss after Alzheimer's disease (AD). Currently, there is no cure available. The etiology, pathophysiology and clinical manifestations of VaD are extremely heterogeneous, but the impaired cerebral blood flow (CBF) represents a common denominator of VaD. The latter might be the result of atherosclerosis, amyloid angiopathy, microbleeding and micro-strokes, together causing blood-brain barrier (BBB) dysfunction and vessel leakage, collectively originating from the consequence of hypertension, one of the main risk factors for VaD. At the histopathological level, VaD displays abnormal vascular remodeling, endothelial cell death, string vessel formation, pericyte responses, fibrosis, astrogliosis, sclerosis, microglia activation, neuroinflammation, demyelination, white matter lesions, deprivation of synapses and neuronal loss. The transforming growth factor (TGF) β has been identified as one of the key molecular factors involved in the aforementioned various pathological aspects. Thus, targeting TGF-β signaling in the brain might be a promising therapeutic strategy to mitigate vascular pathology and improve cognitive functions in patients with VaD. This review revisits the recent understanding of the role of TGF-β in VaD and associated pathological hallmarks. It further explores the potential to modulate certain aspects of VaD pathology by targeting TGF-β signaling.

Potential Role of Circulating Endoglin in Hypertension via the Upregulated Expression of BMP4

Endoglin is a membrane glycoprotein primarily expressed by the vascular endothelium and involved in cardiovascular diseases. Upon the proteolytic processing of the membrane-bound protein, a circulating form of endoglin (soluble endoglin, sEng) can be released, and high levels of sEng have been observed in several endothelial-related pathological conditions, where it appears to contribute to endothelial dysfunction. Preeclampsia is a multisystem disorder of high prevalence in pregnant women characterized by the onset of high blood pressure and associated with increased levels of sEng. Although a pathogenic role for sEng involving hypertension has been reported in several animal models of preeclampsia, the exact molecular mechanisms implicated remain to be identified. To search for sEng-induced mediators of hypertension, we analyzed the protein secretome of human endothelial cells in the presence of sEng. We found that sEng induces the expression of BMP4 in endothelial cells, as evidenced by their proteomic signature, gene transcript levels, and BMP4 promoter activity. A mouse model of preeclampsia with high sEng plasma levels (sEng⁺) showed increased transcript levels of BMP4 in lungs, stomach, and duodenum, and increased circulating levels of BMP4, compared to those of control animals. In addition, after crossing female wild type with male sEng⁺ mice, hypertension appeared 18 days after mating, coinciding with the appearance of high plasma levels of BMP4. Also, serum levels of sEng and BMP4 were positively correlated in pregnant women with and without preeclampsia. Interestingly, sEng-induced arterial pressure elevation in sEng⁺ mice was abolished in the presence of the BMP4 inhibitor noggin, suggesting that BMP4 is a downstream mediator of sEng. These results provide a better understanding on the role of sEng in the physiopathology of preeclampsia and other cardiovascular diseases, where sEng levels are increased.

Endoglin Protein Interactome Profiling Identifies TRIM21 and Galectin-3 as New Binding Partners

Endoglin is a 180-kDa glycoprotein receptor primarily expressed by the vascular endothelium and involved in cardiovascular disease and cancer. Heterozygous mutations in the endoglin gene (ENG) cause hereditary hemorrhagic telangiectasia type 1, a vascular disease that presents with nasal and gastrointestinal bleeding, skin and mucosa telangiectases, and arteriovenous malformations in internal organs. A circulating form of endoglin (alias soluble endoglin, sEng), proteolytically released from the membrane-bound protein, has been observed in several inflammation-related pathological conditions and appears to contribute to endothelial dysfunction and cancer development through unknown mechanisms. Membrane-bound endoglin is an auxiliary component of the TGF-β receptor complex and the extracellular region of endoglin has been shown to interact with types I and II TGF-β receptors, as well as with BMP9 and BMP10 ligands, both members of the TGF-β family. To search for novel protein interactors, we screened a microarray containing over 9000 unique human proteins using recombinant sEng as bait. We find that sEng binds with high affinity, at least, to 22 new proteins. Among these, we validated the interaction of endoglin with galectin-3, a secreted member of the lectin family with capacity to bind membrane glycoproteins, and with tripartite motif-containing protein 21 (TRIM21), an E3 ubiquitin-protein ligase. Using human endothelial cells and Chinese hamster ovary cells, we showed that endoglin co-immunoprecipitates and co-localizes with galectin-3 or TRIM21. These results open new research avenues on endoglin function and regulation.

Surface markers: An identity card of endothelial cells

All endothelial cells have the common characteristic that they line the vessels of the blood circulatory system. However, endothelial cells display a large degree of heterogeneity in the function of their location in the vascular tree. In this article, we have summarized the expression patterns of a number of well-accepted endothelial surface markers present in normal microvascular endothelial cells, arterial and venous endothelial cells, lymphatic endothelial cells, tumor endothelial cells, and endothelial precursor cells.

Spectrum of Novel Hereditary Hemorrhagic Telangiectasia Variants in an Austrian Patient Cohort

Objectives

Hereditary hemorrhagic telangiectasia (HHT) is a rare autosomal dominant genetic disorder characterized by pathogenic blood vessel development and maintenance. HHT type 1 (HHT1) and type 2 (HHT2) are caused by variants in endoglin (ENG) and activin receptor-like kinase-1 (ACVRL1), respectively. The aim of this study was to identify the spectrum of pathogenic variants in ENG and ACVRL1 in Austrian HHT families.

Methods

In this prospective study, eight Austrian HHT families were screened for variants in ENG and ACVRL1 by polymerase chain reaction amplification and sequencing of DNA isolated from peripheral blood.

Results

Heterozygous variants were identified in all families under study. HHT1 was caused by a novel c.816+1G>A splice donor variant, a novel c.1479C>A nonsense (p.Cys493X) variant and a published c.1306C>T nonsense (p.Gln436X) variant in ENG. Variants found in ACVRL1 were novel c.200G>C (p.Arg67Pro) and known c.772G>A (p.Gly258Ser) missense variants in highly conserved residues, a known heterozygous c.100dupT frameshift (p.Cys34Leufs*4) and the known c.1204G>A missense (p.Gly402Ser) and c.1435C>T nonsense (p.Arg479X) variants as causes of HHT2.

Conclusion

Novel and published variants in ENG (37.5%) and ACVRL1 (62.5%) were exclusively identified as the cause of HHT in an Austrian patient cohort. Identification of novel causative genetics variants should facilitate the development of tailored therapeutical applications in the future treatment of autosomal dominant HHT.

Characterization of a mutation in the zona pellucida module of Endoglin that causes Hereditary Hemorrhagic Telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) is a vascular rare disease characterized by nose and gastrointestinal bleeding, skin and mucosa telangiectasias, and arteriovenous malformations in internal organs. HHT shows an autosomal dominant inheritance and a worldwide prevalence of approximately 1:5000 individuals. In >80% of patients, HHT is caused by mutations in either ENG (HHT1) or ACVRL1 (HHT2) genes, which code for the membrane proteins Endoglin and Activin A Receptor Type II-Like Kinase 1 (ALK1), respectively, both belonging to the TGF-β/BMP signaling pathway. In this work, we describe a novel mutation in exon 9 of ENG (c.1145 G > A) found in five affected members of a family, all of them with characteristic symptoms of HHT. This mutation involves Cys382 residue of the Endoglin protein (p.Cys382 > Tyr) in the zona pellucida (ZP) module of its extracellular region. This is a critical residue involved in a conserved intrachain disulphide bond and in the correct folding of the protein. In fact, transfection studies in human cells using Endoglin expression vectors demonstrated that the p.Cys382 > Tyr mutation results in a marked reduction in the levels of the Endoglin protein. These results demonstrate the pathogenic role for this variant in HHT1 and confirm the key function of Cys382 in Endoglin expression.

Soluble endoglin regulates expression of angiogenesis-related proteins and induction of arteriovenous malformations in a mouse model of hereditary hemorrhagic telangiectasia

Endoglin is a transmembrane glycoprotein expressed in vascular endothelium that plays a key role in angiogenesis. Mutations in the endoglin gene (ENG) cause hereditary hemorrhagic telangiectasia type 1 (HHT1), characterized by arteriovenous malformations (AVMs) in different organs. These vascular lesions derive from abnormal processes of angiogenesis, whereby aberrant vascular remodeling leads to focal loss of capillaries. Current treatments for HHT1 include antiangiogenic therapies. Interestingly, a circulating form of endoglin (also known as soluble endoglin, sEng), proteolytically released from the membrane-bound protein and displaying antiangiogenic activity, has been described in several endothelial-related pathological conditions. Using human and mouse endothelial cells, we find that sEng downregulates several pro-angiogenic and pro-migratory proteins involved in angiogenesis. However, this effect is much reduced in endothelial cells that lack endogenous transmembrane endoglin, suggesting that the antiangiogenic activity of sEng is dependent on the presence of endogenous transmembrane endoglin protein. In fact, sEng partially restores the phenotype of endoglin-silenced endothelial cells to that of normal endothelial cells. Moreover, using an established neonatal retinal model of HHT1 with depleted endoglin in the vascular endothelium, sEng treatment decreases the number of AVMs and has a normalizing effect on the vascular phenotype with respect to vessel branching, vascular density and migration of the vascular plexus towards the retinal periphery. Taken together, these data show that circulating sEng can influence vascular development and AVMs by modulating angiogenesis, and that its effect on endothelial cells depends on the expression of endogenous endoglin.

This article has an associated First Person interview with the first author of the paper.

Summary: Soluble endoglin regulates vascular development and arteriovenous malformations by modulating angiogenesis, and its effect on endothelial cells depends on expression of endogenous membrane-bound endoglin.

Inactivating mutations in Drosha mediate vascular abnormalities similar to hereditary hemorrhagic telangiectasia

The transforming growth factor-β (TGF-β) and bone morphogenetic protein (BMP) family of cytokines critically regulates vascular morphogenesis and homeostasis. Impairment of TGF-β or BMP signaling leads to heritable vascular disorders, including hereditary hemorrhagic telangiectasia (HHT). Drosha, a key enzyme for microRNA (miRNA) biogenesis, also regulates the TGF-β and BMP pathway through interaction with Smads and their joint control of gene expression through miRNAs. We report that mice lacking Drosha in the vascular endothelium developed a vascular phenotype resembling HHT that included dilated and disorganized vasculature, arteriovenous fistulae, and hemorrhages. Exome sequencing of HHT patients who lacked known pathogenic mutations revealed an overrepresentation of rare nonsynonymous variants of DROSHA Two of these DROSHA variants (P100L and R279L) did not interact with Smads and were partially catalytically active. In zebrafish, expression of these mutants or morpholino-directed knockdown of Drosha resulted in angiogenesis defects and abnormal vascular permeability. Together, our studies point to an essential role of Drosha in vascular development and the maintenance of vascular integrity, and reveal a previously unappreciated link between Drosha dysfunction and HHT.

Human endoglin as a potential new partner involved in platelet-endothelium interactions

Complex interactions between platelets and activated endothelium occur during the thrombo-inflammatory reaction at sites of vascular injuries and during vascular hemostasis. The endothelial receptor endoglin is involved in inflammation through integrin-mediated leukocyte adhesion and transmigration; and heterozygous mutations in the endoglin gene cause hereditary hemorrhagic telangiectasia type 1. This vascular disease is characterized by a bleeding tendency that is postulated to be a consequence of telangiectasia fragility rather than a platelet defect, since platelets display normal functions in vitro in this condition. Here, we hypothesize that endoglin may act as an adhesion molecule involved in the interaction between endothelial cells and platelets through integrin recognition. We find that the extracellular domain of human endoglin promotes specific platelet adhesion under static conditions and confers resistance of adherent platelets to detachment upon exposure to flow. Also, platelets adhere to confluent endothelial cells in an endoglin-mediated process. Remarkably, Chinese hamster ovary cells ectopically expressing the human αIIbβ3 integrin acquire the capacity to adhere to myoblast transfectants expressing human endoglin, whereas platelets from Glanzmann’s thrombasthenia patients lacking the αIIbβ3 integrin are defective for endoglin-dependent adhesion to endothelial cells. Furthermore, the bleeding time, but not the prothrombin time, is significantly prolonged in endoglin-haplodeficient (Eng^+/−) mice compared to Eng^+/+ animals. These results suggest a new role for endoglin in αIIbβ3 integrin-mediated adhesion of platelets to the endothelium, and may provide a better understanding on the basic cellular mechanisms involved in hemostasis and thrombo-inflammatory events.

Co-injection of mesenchymal stem cells with endothelial progenitor cells accelerates muscle recovery in hind limb ischemia through an endoglin-dependent mechanism

Endothelial colony-forming cells (ECFCs) are progenitor cells committed to endothelial lineages and have robust vasculogenic properties. Mesenchymal stem cells (MSCs) have been described to support ECFC-mediated angiogenic processes in various matrices. However, MSC-ECFC interactions in hind limb ischemia (HLI) are largely unknown. Here we examined whether co-administration of ECFCs and MSCs bolsters vasculogenic activity in nude mice with HLI. In addition, as we have previously shown that endoglin is a key adhesion molecule, we evaluated its involvement in ECFC/MSC interaction. Foot perfusion increased on day 7 after ECFC injection and was even better at 14 days. Co-administration of MSCs significantly increased vessel density and foot perfusion on day 7 but the differences were no longer significant at day 14. Analysis of mouse and human CD31, and in situ hybridization of the human ALU sequence, showed enhanced capillary density in ECFC+MSC mice. When ECFCs were silenced for endoglin, coinjection with MSCs led to lower vessel density and foot perfusion at both 7 and 14 days (p<0.001). Endoglin silencing in ECFCs did not affect MSC differentiation into perivascular cells or other mesenchymal lineages. Endoglin silencing markedly inhibited ECFC adhesion to MSCs. Thus, MSCs, when combined with ECFCs, accelerate muscle recovery in a mouse model of hind limb ischemia, through an endoglin-dependent mechanism.

Neuropilin 1 Involvement in Choroidal and Retinal Neovascularisation

PURPOSE

Inhibiting VEGF is the gold standard treatment for neovascular age-related macular degeneration (AMD). It is also effective in preventing retinal oedema and neovascularisation (NV) in diabetic retinopathy (DR) and retinal vein occlusions (RVO). Neuropilin 1 (Nrp1) is a co-receptor for VEGF and many other growth factors, and therefore a possible alternative drug target in intra ocular neovascular disease. Here we assessed choroidal and retinal NV in an inducible, endothelial specific knock out model for Nrp1.

METHODS

Crossing Nrp1 floxed mice with Pdgfb-CreERT2 mice produced tamoxifen-inducible, endothelial specific Nrp1 knock out mice (Nrp1ΔEC) and Cre-negative, control littermates. Cre-recombinase activity was confirmed in the Ai3(RCL-EYFP) reporter strain. Animals were subjected to laser-induced CNV (532 nm) and spectral domain-optical coherence tomography (SD-OCT) was performed immediately after laser and at day 7. Fluorescein angiography (FA) evaluated leakage and postmortem lectin staining in flat mounted RPE/choroid complexes was also used to measure CNV. Furthermore, retinal neovascularisation in the oxygen induced retinopathy (OIR) model was assessed by immunohistochemistry in retinal flatmounts.

RESULTS

In vivo FA, OCT and post-mortem lectin staining showed a statistically significant reduction in leakage (p<0.05), CNV volume (p<0.05) and CNV area (p<0.05) in the Nrp1ΔEC mice compared to their Cre-negative littermates. Also the OIR model showed reduced retinal NV in the mutant animals compared to wild types (p<0.001).

CONCLUSION

We have demonstrated reduced choroidal and retinal NV in animals that lack endothelial Nrp1, confirming a role of Nrp1 in those processes. Therefore, Nrp1 may be a promising drug target for neovascular diseases in the eye.

The role of endoglin in post-ischemic revascularization

Following arterial occlusion, blood vessels respond by forming a new network of functional capillaries (angiogenesis), by reorganizing preexisting capillaries through the recruitment of smooth muscle cells to generate new arteries (arteriogenesis) and by growing and remodeling preexisting collateral arterioles into physiologically relevant arteries (collateral development). All these processes result in the recovery of organ perfusion. The importance of endoglin in post-occlusion reperfusion is sustained by several observations: (1) endoglin expression is increased in vessels showing active angiogenesis/remodeling; (2) genetic endoglin haploinsufficiency in humans causes deficient angiogenesis; and (3) the reduction of endoglin expression by gene disruption or the administration of endoglin-neutralizing antibodies reduces angiogenesis and revascularization. However, the precise role of endoglin in the several processes associated with revascularization has not been completely elucidated and, in some cases, the function ascribed to endoglin by different authors is controversial. The purpose of this review is to organize in a critical way the information available for the role of endoglin in several phenomena (angiogenesis, arteriogenesis and collateral development) associated with post-ischemic revascularization.

Hereditary Hemorrhagic Telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) is an underrecognized and underdiagnosed autosomal-dominant angiodysplasia that has an estimated prevalence of 1 in 5000 individuals, with variable clinical presentations even within family members with identical mutations. The most common manifestations are telangiectasias of the skin and nasal mucosa. However, HHT can often be complicated by the presence of arteriovenous malformations and telangiectasias in the lungs, brain, gastrointestinal tract, and liver that are often silent and can lead to life-threatening complications of stroke and hemorrhage. This article reviews HHT for the pulmonologist, who is not uncommonly the first practitioner to encounter these patients.

Biodegradable Mg-Cu alloys with enhanced osteogenesis, angiogenesis, and long-lasting antibacterial effects

A series of biodegradable Mg-Cu alloys is designed to induce osteogenesis, stimulate angiogenesis, and provide long-lasting antibacterial performance at the same time. The Mg-Cu alloys with precipitated Mg2Cu intermetallic phases exhibit accelerated degradation in the physiological environment due to galvanic corrosion and the alkaline environment combined with Cu release endows the Mg-Cu alloys with prolonged antibacterial effects. In addition to no cytotoxicity towards HUVECs and MC3T3-E1 cells, the Mg-Cu alloys, particularly Mg-0.03Cu, enhance the cell viability, alkaline phosphatase activity, matrix mineralization, collagen secretion, osteogenesis-related gene and protein expressions of MC3T3-E1 cells, cell proliferation, migration, endothelial tubule forming, angiogenesis-related gene, and protein expressions of HUVECs compared to pure Mg. The favorable osteogenesis and angiogenesis are believed to arise from the release of bioactive Mg and Cu ions into the biological environment and the biodegradable Mg-Cu alloys with osteogenesis, angiogenesis, and long-term antibacterial ability are very promising in orthopedic applications.

VCAM-1+ placenta chorionic villi-derived mesenchymal stem cells display potent pro-angiogenic activity

Introduction

Mesenchymal stem cells (MSCs) represent a heterogeneous cell population that is promising for regenerative medicine. The present study was designed to assess whether VCAM-1 can be used as a marker of MSC subpopulation with superior angiogenic potential.

Methods

MSCs were isolated from placenta chorionic villi (CV). The VCAM-1^+/− CV-MSCs population were separated by Flow Cytometry and subjected to a comparative analysis for their angiogenic properties including angiogenic genes expression, vasculo-angiogenic abilities on Matrigel in vitro and in vivo, angiogenic paracrine activities, cytokine array, and therapeutic angiogenesis in vascular ischemic diseases.

Results

Angiogenic genes, including HGF, ANG, IL8, IL6, VEGF-A, TGFβ, MMP₂ and bFGF, were up-regulated in VCAM-1⁺CV-MSCs. Consistently, angiogenic cytokines especially HGF, IL8, angiogenin, angiopoitin-2, μPAR, CXCL1, IL-1β, IL-1α, CSF2, CSF3, MCP-3, CTACK, and OPG were found to be significantly increased in VCAM-1⁺ CV-MSCs. Moreover, VCAM-1⁺CV-MSCs showed remarkable vasculo-angiogenic abilities by angiogenesis analysis with Matrigel in vitro and in vivo and the conditioned medium of VCAM-1⁺ CV-MSCs exerted markedly pro-proliferative and pro-migratory effects on endothelial cells compared to VCAM-1⁻CV-MSCs. Finally, transplantation of VCAM-1⁺CV-MSCs into the ischemic hind limb of BALB/c nude mice resulted in a significantly functional improvement in comparison with VCAM-1⁻CV-MSCs transplantation.

Conclusions

VCAM-1⁺CV-MSCs possessed a favorable angiogenic paracrine activity and displayed therapeutic efficacy on hindlimb ischemia. Our results suggested that VCAM-1⁺CV-MSCs may represent an important subpopulation of MSC for efficient therapeutic angiogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0297-0) contains supplementary material, which is available to authorized users.

Leucine-rich α-2-glycoprotein promotes TGFβ1-mediated growth suppression in the Lewis lung carcinoma cell lines

Leucine-rich α2-glycoprotein (LRG) is an approximately 50-kDa glycoprotein that has been found to be elevated in the sera of patients with several types of cancer. LRG directly binds to transforming growth factor beta 1 (TGFβ1) and modulates TGFβ1 signaling in endothelial cells; however, the precise function of LRG in cancer remains unclear. This study aimed to investigate the role of LRG in cancer. Lewis lung carcinoma (LLC) cells hardly expressed LRG. The growth of LLC tumors allografted in the LRG knockout (KO) mice was significantly increased compared with wild-type (WT) mice. Conversely, overexpression of LRG significantly inhibited the growth of LLC tumors in WT mice. In the presence of LRG, TGFβ1 significantly inhibited the proliferation of LLC cells and human hepatocellular carcinoma Hep3B cells in vitro by inducing apoptosis via the potent activation of smad2 and its downstream signaling pathway. Furthermore, administration of a TGFβR1 inhibitor (SB431542) significantly enhanced the growth of LLC tumors in WT mice compared with LRG KO mice via inhibition of apoptosis. We propose that LRG potentiates the effect of TGFβ1 in cancer cells whose growth is suppressed in the presence of TGFβ1.

Transcription factor KLF6 upregulates expression of metalloprotease MMP14 and subsequent release of soluble endoglin during vascular injury

After endothelial injury, the transcription factor Krüppel-like factor 6 (KLF6) translocates into the cell nucleus to regulate a variety of target genes involved in angiogenesis, vascular repair and remodeling, including components of the membrane transforming growth factor beta (TGF-β) receptor complex such as endoglin and activin receptor-like kinase 1. The membrane metalloproteinase 14 (MMP14 or MT1-MMP) targets endoglin to release soluble endoglin and is involved in vascular inflammation and endothelial tubulogenesis. However, little is known about the regulation of MMP14 expression during vascular wounding. In vitro denudation of monolayers of human endothelial cell monolayers leads to an increase in the KLF6 gene transcriptional rate, followed by an upregulation of MMP14 and release of soluble endoglin. Concomitant with this process, MMP14 co-localizes with endoglin in the sprouting endothelial cells surrounding the wound border. MMP14 expression at mRNA and protein levels is increased by ectopic KLF6 and downregulated by KLF6 suppression in cultured endothelial cells. Moreover, after wire-induced endothelial denudation, Klf6^+/− mice show lower levels of MMP14 in their vasculature compared with their wild-type siblings. Ectopic cellular expression of KLF6 results in an increased transcription rate of MMP14, and chromatin immunoprecipitation assays show that KLF6 interacts with MMP14 promoter in ECs, this interaction being enhanced during wound healing. Furthermore, KLF6 markedly increases the transcriptional activity of different reporter constructs of MMP14 gene promoter. These results suggest that KLF6 regulates MMP14 transcription and is a critical player of the gene expression network triggered during endothelial repair.

Genome-wide transcriptional and functional analysis of endoglin isoforms in the human promonocytic cell line U937

Endoglin is an auxiliary cell surface receptor for TGF-β family members. Two different alternatively spliced isoforms, long (L)-endoglin and short (S)-endoglin, have been reported. S-endoglin and L-endoglin proteins vary from each other in their cytoplasmic tails that contain 14 and 47 amino acids, respectively. A critical role for endoglin in vascular development has primarily been studied in endothelial cells. In addition, endoglin expression is upregulated during monocyte-to-macrophage differentiation; however, little is known about its role in this myeloid context. To investigate the function of endoglin in monocytes, stable transfectants expressing the two endoglin isoforms in the promonocytic human cell line U937 were generated. The differential gene expression fingerprinting of these endoglin transfectants using DNA microarrays and further bioinformatics analysis showed a clear alteration in essential biological functions, mainly those related to "Cellular Movement", including cell adhesion and transmigration. Interestingly, these cellular functions are highly dependent on adhesion molecules, including integrins α1 (CD49a, ITGA1 gene), αL (CD11a, ITGAL gene), αM (CD11b, ITGAM gene) and β2 (CD18, ITGB2 gene) and the chemokine receptor CCR2 (CD192, CCR2 gene), which are downregulated in endoglin transfectants. Moreover, activin A (INHBA gene), a TGF-β superfamily member involved in macrophage polarization, was distinctly affected in each endoglin transfectant, and may contribute to the regulated expression of integrins. These data were confirmed by quantitative PCR, flow cytometry and functional tests. Taken together, these results provide new insight into endoglin function in monocytes.

Pivotal role for decorin in angiogenesis

Angiogenesis, the formation of new blood vessels from preexisting vessels, is a highly complex process. It is regulated in a finely-tuned manner by numerous molecules including not only soluble growth factors such as vascular endothelial growth factor and several other growth factors, but also a diverse set of insoluble molecules, particularly collagenous and non-collagenous matrix constituents. In this review we have focused on the role and potential mechanisms of a multifunctional small leucine-rich proteoglycan decorin in angiogenesis. Depending on the cellular and molecular microenvironment where angiogenesis occurs, decorin can exhibit either a proangiogenic or an antiangiogenic activity. Nevertheless, in tumorigenesis-associated angiogenesis and in various inflammatory processes, particularly foreign body reactions and scarring, decorin exhibits an antiangiogenic activity, thus providing a potential basis for the development of decorin-based therapies in these pathological situations.

Endostatin and kidney fibrosis in aging: a case for antagonistic pleiotropy?

A recurring theme of a host of gerontologic studies conducted in either experimental animals or in humans is related to documenting the functional decline with age. We hypothesize that elevated circulating levels of a powerful antiangiogenic peptide, endostatin, represent one of the potent systemic causes for multiorgan microvascular rarefaction and functional decline due to fibrosis. It is possible that during the life span of an organism there is an accumulation of dormant transformed cells producing antiangiogenic substances (endostatin) that maintain the dormancy of such scattered malignant cells. The proof of this postulate cannot be obtained by physically documenting these scattered cells, and it rests exclusively on the detection of sequelae of shifted pro- and antiangiogenic balance toward the latter. Here we compared circulating levels of endostatin in young and aging mice of two different strains and showed that endostatin levels are elevated in the latter. Renal expression of endostatin increased ~5.6-fold in aging animals. This was associated with microvascular rarefaction and progressive tubulointerstitial fibrosis. In parallel, the levels of sirtuins 1 and 3 were significantly suppressed in aging mice in conjunction with the expression of markers of senescence. Treating young mice with endostatin for 28 days showed delayed recovery of circulation after femoral artery ligation and reduced patency of renal microvasculature but no fibrosis. In conclusion, the findings are consistent with the hypothesis on elevation of endostatin levels and parallel microvascular rarefaction and induction of renal fibrosis in aging mice.

TGF-β cascade regulation by PPP1 and its interactors -impact on prostate cancer development and therapy

Protein phosphorylation is a key mechanism by which normal and cancer cells regulate their main transduction pathways. Protein kinases and phosphatases are precisely orchestrated to achieve the (de)phosphorylation of candidate proteins. Indeed, cellular health is dependent on the fine-tune of phosphorylation systems, which when deregulated lead to cancer. Transforming growth factor beta (TGF-β) pathway involvement in the genesis of prostate cancer has long been established. Many of its members were shown to be hypo- or hyperphosphorylated during the process of malignancy. A major phosphatase that is responsible for the vast majority of the serine/threonine dephosphorylation is the phosphoprotein phosphatase 1 (PPP1). PPP1 has been associated with the dephosphorylation of several proteins involved in the TGF-β cascade. This review will discuss the role of PPP1 in the regulation of several TGF-β signalling members and how the subversion of this pathway is related to prostate cancer development. Furthermore, current challenges on the protein phosphatases field as new targets to cancer therapy will be addressed.

A functional genomic approach reveals the transcriptional role of EDD in the expression and function of angiogenesis regulator ACVRL1

EDD (E3 isolated by differential display) was initially isolated as a progestin-regulated gene in breast cancer cells, and represents the human ortholog of the Drosophila melanogaster hyperplastic discs gene (hyd). It encodes a highly conserved and predominantly nuclear ubiquitin E3 ligase of the HECT family, with potential multifunctional roles in development and tumorigenesis. In this study, we further examined the largely uncharacterized role of EDD in transcriptional regulation by uncovering the spectrum of its direct target genes at a genome-wide level. Use of a systematic approach that integrates gene expression and chromatin binding profiling identified several candidate EDD-target genes, one of which is ACVRL1, a TGF-β receptor with functional implications in blood vessel development. Further characterization revealed a negative regulation of ACVRL1 gene expression by EDD that is exerted at the promoter. Consistent with the aberrant upregulation of ACVRL1 and downstream Smad signaling, abrogation of EDD led to deregulated vessel development and endothelial cell motility. Collectively, these results extended the known cellular roles of EDD to critical functions in transcriptional regulation as well as angiogenesis, and may provide mechanistic explanations for EDD's tumorigenic and developmental roles.

Endothelial sirtuin 1 deficiency perpetrates nephrosclerosis through downregulation of matrix metalloproteinase-14: relevance to fibrosis of vascular senescence

Sirtuin 1 (SIRT1) depletion in vascular endothelial cells mediates endothelial dysfunction and premature senescence in diverse cardiovascular and renal diseases. However, the molecular mechanisms underlying these pathologic effects remain unclear. Here, we examined the phenotype of a mouse model of vascular senescence created by genetically ablating exon 4 of Sirt1 in endothelial cells (Sirt1(endo-/-)). Under basal conditions, Sirt1(endo-/-) mice showed impaired endothelium-dependent vasorelaxation and angiogenesis, and fibrosis occurred spontaneously at low levels at an early age. In contrast, induction of nephrotoxic stress (acute and chronic folic acid-induced nephropathy) in Sirt1(endo-/-) mice resulted in robust acute renal functional deterioration followed by an exaggerated fibrotic response compared with control animals. Additional studies identified matrix metalloproteinase-14 (MMP-14) as a target of SIRT1. In the kidneys of Sirt1(endo-/-) mice, impaired angiogenesis, reduced matrilytic activity, and retention of the profibrotic cleavage substrates tissue transglutaminase and endoglin accompanied MMP-14 suppression. Furthermore, restoration of MMP-14 expression in SIRT1-depeleted mice improved angiogenic and matrilytic functions of the endothelium, prevented renal dysfunction, and attenuated nephrosclerosis. Our findings establish a novel mechanistic molecular link between endothelial SIRT1 depletion, downregulation of MMP-14, and the development of nephrosclerosis.

MiR-205 is downregulated in hereditary hemorrhagic telangiectasia and impairs TGF-beta signaling pathways in endothelial cells

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disorder characterized by arteriovenous malformations and hemorrhages. This vascular disease results mainly from mutations in 2 genes involved in the TGF-β pathway (ENG and ALK1) that are exclusively expressed by endothelial cells. The present study identified miR-27a and miR-205 as two circulating miRNAs differentially expressed in HHT patients. The plasma levels of miR-27a are elevated while those of miR-205 are reduced in both HHT1 and HHT2 patients compared to healthy controls. The role of miR-205 in endothelial cells was further investigated. Our data indicates that miR-205 expression displaces the TGF-β balance towards the anti-angiogenic side by targeting Smad1 and Smad4. In line, overexpression of miR-205 in endothelial cells reduces proliferation, migration and tube formation while its inhibition shows opposite effects. This study not only suggests that detection of circulating miRNA (miR-27a and miR-205) could help for the screening of HHT patients but also provides a functional link between the deregulated expression of miR-205 and the HHT phenotype.

High glucose facilitates cell cycle arrest of rat bone marrow multipotent adult progenitor cells through transforming growth factor-β1 and extracellular signal-regulated kinase 1/2 signalling without changing Oct4 expression

1. The transcription factor Oct4 is critical to the pluripotency, self-renewal and differentiation of stem cells. The aim of the present study was to investigate the effects of high glucose (HG) on the cell cycle progression of bone marrow multipotent adult progenitor cells (MAPC) and Oct4 expression, as well as the underlying mechanisms. 2. Rat MAPC were cultured in normal (5.5 mmol/L D-glucose) and HG (25.5 mmol/L D-glucose) media for up to 14 days. L-Glucose served as a high osmolarity control. Culture in HG media substantially increased the number of cells in the G(0)/G(1) phase and decreased the number in the S phase without changing the cell population in the G(2) phase. Expression of the cell cycle regulatory protein p21CIP/WAF-1 (p21), but not that of p27KIP-1 (p27), was significantly upregulated in cells cultured in HG media. Significant increases were seen in transforming growth factor (TGF)-β1 levels in cells and MAPC-conditioned medium in the presence of HG, and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation was enhanced in cells cultured in the presence of HG medium without any changes in Akt phosphorylation. 3. Neutralizing TGF-β1 antibody effectively prevented HG-induced increases in ERK1/2 phosphorylation, p21 expression and suppression of cell cycle progression of MAPC. Inhibiting ERK1/2 phosphorylation with PD98059 completely blocked HG-induced p21 expression and markedly reversed HG-induced inhibition of cell cycle progression in MAPC. The HG-induced suppression of cell cycle progression was not accompanied by inhibition of cell proliferation or Oct4 expression in these cells. 4. The data indicate that HG facilitates cell cycle arrest of rat MAPC through TGF-β1-induced activation of ERK1/2 signalling and p21 expression, and that Oct4 expression in MAPC is independent of the cell cycle and/or TGF-β1 or ERK1/2 signalling in HG medium.

Heterozygous deficiency of endoglin decreases insulin and hepatic triglyceride levels during high fat diet

Endoglin is a transmembrane auxiliary receptor for transforming growth factor-beta (TGF-beta) that is predominantly expressed on proliferating endothelial cells. It plays a wide range of physiological roles but its importance on energy balance or insulin sensitivity has been unexplored. Endoglin deficient mice die during midgestation due to cardiovascular defects. Here we report for first time that heterozygous endoglin deficiency in mice decreases high fat diet-induced hepatic triglyceride content and insulin levels. Importantly, these effects are independent of changes in body weight or adiposity. At molecular level, we failed to detect relevant changes in the insulin signalling pathway at basal levels in liver, muscle or adipose tissues that could explain the insulin-dependent effect. However, we found decreased triglyceride content in the liver of endoglin heterozygous mice fed a high fat diet in comparison to their wild type littermates. Overall, our findings indicate that endoglin is a potentially important physiological mediator of insulin levels and hepatic lipid metabolism.

Robustness in angiogenesis: notch and BMP shaping waves

Vascular patterning involves sprouting of blood vessels, which is governed by orchestrated communication between cells in the surrounding tissue and endothelial cells (ECs) lining the blood vessels. Single ECs are selected for sprouting by hypoxia-induced stimuli and become the 'tip' or leader cell that guides new sprouts. The 'stalk' or trailing ECs proliferate for tube extension and lumenize the nascent vessel. Stalk and tip cells can dynamically switch their identities during this process in a Notch-dependent manner. Here, we review recent studies showing that bone morphogenetic protein (BMP) signaling coregulates Notch target genes in ECs. In particular, we focus on how Delta-like ligand 4 (DLL4)-Notch and BMP effector interplay may drive nonsynchronized oscillatory gene expression in ECs essential for setting sharp tip-stalk cell boundaries while sustaining a dynamic pool of nonsprouting ECs. Deeper knowledge about the coregulation of vessel plasticity in different vascular beds may result in refinement of anti-angiogenesis and vessel normalization therapies.

Endothelial endoglin is involved in inflammation: role in leukocyte adhesion and transmigration

Human endoglin is an RGD-containing transmembrane glycoprotein identified in vascular endothelial cells. Although endoglin is essential for angiogenesis and its expression is up-regulated in inflammation and at sites of leukocyte extravasation, its role in leukocyte trafficking is unknown. This function was tested in endoglin heterozygous mice (Eng(+/-)) and their wild-type siblings Eng(+/+) treated with carrageenan or LPS as inflammatory agents. Both stimuli showed that inflammation-induced leukocyte transendothelial migration to peritoneum or lungs was significantly lower in Eng(+/-) than in Eng(+/+) mice. Leukocyte transmigration through cell monolayers of endoglin transfectants was clearly enhanced in the presence of endoglin. Coating transwells with the RGD-containing extracellular domain of endoglin, enhanced leukocyte transmigration, and this increased motility was inhibited by soluble endoglin. Leukocytes stimulated with CXCL12, a chemokine involved in inflammation, strongly adhered to endoglin-coated plates and to endoglin-expressing endothelial cells. This endoglin-dependent adhesion was abolished by soluble endoglin, RGD peptides, the anti-integrin α5β1 inhibitory antibody LIA1/2 and the chemokine receptor inhibitor AMD3100. These results demonstrate for the first time that endothelial endoglin interacts with leukocyte integrin α5β1 via its RGD motif, and this adhesion process is stimulated by the inflammatory chemokine CXCL12, suggesting a regulatory role for endoglin in transendothelial leukocyte trafficking.

Genomic determinants of normal tissue toxicity after radiotherapy for head and neck malignancy: a systematic review

Interindividual variations in radiotoxicity responses exist despite uniform treatment protocols. It is speculated that normal genetic variants, particularly single nucleotide polymorphisms (SNPs) may influence normal head and neck (HN) tissue radiotoxicity. This first-ever systematic review was undertaken to evaluate the association of SNPs with normal HN tissues radiotoxicity. Multiple databases (1950-February 2012) were reviewed using a combination of related keywords and MeSH terms. All published HN radiotoxicity studies with sufficient relevant data for extraction were included. The outcomes evaluated were acute and late radiotoxicity endpoints. Methodological quality assessment based on the STrengthening the REporting of Genetic Association (STREGA) statement was performed. Seven articles from 692 articles searched fulfilled the eligibility criteria. Recruited sample sizes were small (range, 32-140). There were 5/7 case-control studies. All studies used multimodality treatment with heterogeneous radiation parameters. Candidate gene approach was used in all studies. Fourteen SNPs from 9 genes were evaluated from the following pathways: DNA damage response, radiation fibrogenesis and oxidative/xenobiotic metabolism. Acute radiotoxicity events were associated with SNPs of DNA repair genes (OR, 3.01-4.08). SNPs of TGFβ1 were associated with osteoradionecrosis (OR, 4.2) and subcutaneous fibrosis. Genetic association studies in HN radiotoxicity currently provide hypothesis-generating findings that require validation in larger studies. Future studies must incorporate critical methodological issues and technological improvements, including using a genome-wide approach. Headway is possible through case-pooling of existing clinical trial data which could create a larger sample size of well-characterized treatment and endpoints. Also, on-going HN cancer clinical trials should consider extending their toxicity evaluation to include genetic association studies.

Endothelial expression of TGFβ type II receptor is required to maintain vascular integrity during postnatal development of the central nervous system

TGFβ signalling in endothelial cells is important for angiogenesis in early embryonic development, but little is known about its role in early postnatal life. To address this we used a tamoxifen inducible Cre-LoxP strategy in neonatal mice to deplete the TypeII TGFβ receptor (Tgfbr2) specifically in endothelial cells. This resulted in multiple micro-haemorrhages, and glomeruloid-like vascular tufts throughout the cerebral cortices and hypothalamus of the brain as well as in retinal tissues. A detailed examination of the retinal defects in these mutants revealed that endothelial adherens and tight junctions were in place, pericytes were recruited and there was no failure of vascular smooth muscle differentiation. However, the deeper retinal plexus failed to form in these mutants and the angiogenic sprouts stalled in their progress towards the inner nuclear layer. Instead the leading endothelial cells formed glomerular tufts with associated smooth muscle cells. This evidence suggests that TGFβ signalling is not required for vessel maturation, but is essential for the organised migration of endothelial cells as they begin to enter the deeper layers of the retina. Thus, TGFβ signalling is essential in vascular endothelial cells for maintaining vascular integrity at the angiogenic front as it migrates into developing neural tissues in early postnatal life.

Advances in the cellular and molecular biology of angiogenesis

Capillaries have been recognized for over a century as one of the most important components in regulating tissue oxygen transport, and their formation or angiogenesis a pivotal element of tissue remodelling during development and adaptation. Clinical interest stems from observations that both excessive and inadequate vascular growth plays a major role in human diseases, and novel developments in treatments for cancer and eye disease increasingly rely on anti-angiogenic therapies. Although the discovery of VEGF (vascular endothelial growth factor) provided the first clue for specificity of signalling in endothelial cell activation, understanding the integrative response that drives angiogenesis requires a much broader perspective. The Advances in the Cellular and Molecular Biology of Angiogenesis meeting brought together researchers at the forefront of this rapidly moving field to provide an update on current understanding, and the most recent insights into molecular and cellular mechanisms of vascular growth. The plenary lecture highlighted the integrative nature of the angiogenic process, whereas invited contributions from basic and clinician scientists described fundamental mechanisms and disease-associated issues of blood vessel formation, grouped under a number of themes to aid discussion. These articles will appeal to academic, clinical and pharmaceutical scientists interested in the molecular and cellular basis of angiogenesis, their modulation or dysfunction in human diseases, and application of these findings towards translational medicine.