Oral vitamin C restores endothelial function during acute inflammation in young and older adults

Oxidative stress has been linked to reductions in vascular function during acute inflammation in young adults; however, the effect of acute inflammation on vascular function with aging is inconclusive. The aim of this study was to determine if oral antioxidant administration eliminates vascular dysfunction during acute inflammation in young and older adults. Brachial flow-mediated dilation (FMD) and carotid-femoral pulse wave velocity (PWV) were measured in nine young (3 male, 24 ± 4 yrs, 26.2 ± 4.9 kg/m2 ) and 16 older (13 male, 64 ± 5 yrs, 25.8 ± 3.2 kg/m2 ) adults before and 2-h after oral consumption of 2 g of vitamin C. The vitamin C protocol was completed at rest and 24 h after acute inflammation was induced via the typhoid vaccine. Venous blood samples were taken to measure markers of inflammation and vitamin C. Both interleukin-6 (Δ+0.7 ± 1.8 pg/ml) and C-reactive protein (Δ+1.9 ± 3.1 mg/L) were increased at 24 h following the vaccine (p < 0.01). There was no change in FMD or PWV following vitamin C administration at rest (p > 0.05). FMD was lower in all groups during acute inflammation (Δ-1.4 ± 1.9%, p < 0.01), with no changes in PWV (Δ-0.0 ± 0.9 m/s, p > 0.05). Vitamin C restored FMD back to initial values in young and older adults during acute inflammation (Δ+1.0 ± 1.8%, p < 0.01) with no change in inflammatory markers or PWV (p > 0.05). In conclusion, oral vitamin C restored endothelial function during acute inflammation in young and older adults, with no effect on aortic stiffness. The effect of vitamin C on endothelial function did not appear to be due to reductions in inflammatory markers. The exact mechanisms should be further investigated.

Beta-Arrestins and Receptor Signaling in the Vascular Endothelium

The vascular endothelium is the innermost layer of blood vessels and is a key regulator of vascular tone. Endothelial function is controlled by receptor signaling through G protein-coupled receptors, receptor tyrosine kinases and receptor serine-threonine kinases. The β-arrestins, multifunctional adapter proteins, have the potential to regulate all of these receptor families, although it is unclear as to whether they serve to integrate signaling across all of these different axes. Notably, the β-arrestins have been shown to regulate signaling by a number of receptors important in endothelial function, such as chemokine receptors and receptors for vasoactive substances such as angiotensin II, endothelin-1 and prostaglandins. β-arrestin-mediated signaling pathways have been shown to play central roles in pathways that control vasodilation, cell proliferation, migration, and immune function. At this time, the physiological impact of this signaling has not been studied in detail, but a deeper understanding of it could lead to the development of novel therapies for the treatment of vascular disease.

Single-cell gene profiling and lineage tracing analyses revealed novel mechanisms of endothelial repair by progenitors

Stem/progenitor cells (SPCs) have been implicated to participate in vascular repair. However, the exact role of SPCs in endothelial repair of large vessels still remains controversial. This study aimed to delineate the cellular heterogeneity and possible functional role of endogenous vascular SPCs in large vessels. Using single-cell RNA-sequencing (scRNA-seq) and genetic lineage tracing mouse models, we uncovered the cellular heterogeneity of SPCs, i.e., c-Kit+ cells in the mouse aorta, and found that endogenous c-Kit+ cells acquire endothelial cell fate in the aorta under both physiological and pathological conditions. While c-Kit+ cells contribute to aortic endothelial turnover in the atheroprone regions during homeostasis, recipient c-Kit+ cells of nonbone marrow source replace both luminal and microvessel endothelial cells in transplant arteriosclerosis. Single-cell pseudotime analysis of scRNA-seq data and in vitro cell experiments suggest that vascular SPCs display endothelial differentiation potential and undergo metabolic reprogramming during cell differentiation, in which AKT/mTOR-dependent glycolysis is critical for endothelial gene expression. These findings demonstrate a critical role for c-Kit lineage cells in aortic endothelial turnover and replacement, and may provide insights into therapeutic strategies for vascular diseases.

Purinergic P2Y2 receptors modulate endothelial sprouting

Purinergic P2 receptors are critical regulators of several functions within the vascular system, including platelet aggregation, vascular inflammation, and vascular tone. However, a role for ATP release and P2Y receptor signalling in angiogenesis remains poorly defined. Here, we demonstrate that blood vessel growth is controlled by P2Y2 receptors. Endothelial sprouting and vascular tube formation were significantly dependent on P2Y2 expression and inhibition of P2Y2 using a selective antagonist blocked microvascular network generation. Mechanistically, overexpression of P2Y2 in endothelial cells induced the expression of the proangiogenic molecules CXCR4, CD34, and angiopoietin-2, while expression of VEGFR-2 was decreased. Interestingly, elevated P2Y2 expression caused constitutive phosphorylation of ERK1/2 and VEGFR-2. However, stimulation of cells with the P2Y2 agonist UTP did not influence sprouting unless P2Y2 was constitutively expressed. Finally, inhibition of VEGFR-2 impaired spontaneous vascular network formation induced by P2Y2 overexpression. Our data suggest that P2Y2 receptors have an essential function in angiogenesis, and that P2Y2 receptors present a therapeutic target to regulate blood vessel growth.

Endothelialization of cardiovascular devices

Blood-contacting surfaces of cardiovascular devices are not biocompatible for creating an endothelial layer on them. Numerous research studies have mainly sought to modify these surfaces through physical, chemical and biological means to ease early endothelial cell (EC) adhesion, migration and proliferation, and eventually to build an endothelial layer on the surfaces. The first priority for surface modification is inhibition of protein adsorption that leads to inhibition of platelet adhesion to the device surfaces, which may favor EC adhesion. Surface modification through surface texturing, if applicable, can bring some hopeful outcomes in this regard. Surface modifications through chemical and/or biological means may play a significant role in easy endothelialization of cardiovascular devices and inhibit smooth muscle cell proliferation. Cellular engineering of cells relevant to endothelialization can boost the positive outcomes obtained through surface engineering. This review briefly summarizes recent developments and research in early endothelialization of cardiovascular devices. STATEMENT OF SIGNIFICANCE: Endothelialization of cardiovascular implants, including heart valves, vascular stents and vascular grafts is crucial to solve many problems in our health care system. Numerous research efforts have been made to improve endothelialization on the surfaces of cardiovascular implants, mainly through surface modifications in three ways - physically, chemically and biologically. This review is intended to highlight comprehensive research studies to date on surface modifications aiming for early endothelialization on the blood-contacting surfaces of cardiovascular implants. It also discusses future perspectives to help guide endothelialization strategies and inspire further innovations.

Premature Vascular Aging in Guinea Pigs Affected by Fetal Growth Restriction

Cardiovascular risk associated with fetal growth restriction (FGR) could result from an early impaired vascular function. However, whether this effect results in premature vascular aging has not been addressed. We studied the ex vivo reactivity of carotid and femoral arteries in fetal (near term), adults (eight months-old) and aged (16 months-old) guinea pigs in normal (control) and FGR offspring. Additionally, an epigenetic marker of vascular aging (i.e., LINE-1 DNA methylation) was evaluated in human umbilical artery endothelial cells (HUAEC) from control and FGR subjects. Control guinea pig arteries showed an increased contractile response (KCl-induced) and a progressive impairment of NO-mediated relaxing responses as animals get older. FGR was associated with an initial preserved carotid artery reactivity as well as a later significant impairment in NO-mediated responses. Femoral arteries from FGR fetuses showed an increased contractility but a decreased relaxing response compared with control fetuses, and both responses were impaired in FGR-adults. Finally, FGR-HUAEC showed decreased LINE-1 DNA methylation compared with control-HUAEC. These data suggest that the aging of vascular function occurs by changes in NO-mediated responses, with limited alterations in contractile capacity. Further, these effects are accelerated and imposed at early stages of development in subjects exposed to a suboptimal intrauterine environment.

Growth factor signaling pathways in vascular development and disease

Angiogenic blood vessel growth is essential to ensure organs receive adequate blood supply to support normal organ function and homeostasis. Angiogenesis involves a complex series of cellular events through which new vessels grow out from existing vasculature. Growth factor signaling, layered over a range of other signaling inputs, orchestrates this process. The response of endothelial cells (ECs) to growth factor signals must be carefully controlled through feedback mechanisms to prevent excessive vessel growth, remodeling or destabilization. In this article, we summarize recent findings describing how ECs respond to growth factor signals during blood vessel development and homeostasis and how perturbation of these responses can lead to disease.

Low-intensity resistance training with blood flow restriction improves vascular endothelial function and peripheral blood circulation in healthy elderly people

PURPOSE

The present study aimed to investigate the effects of low-intensity resistance training with blood flow restriction (BFR resistance training) on vascular endothelial function and peripheral blood circulation.

METHODS

Forty healthy elderly volunteers aged 71 ± 4 years were divided into two training groups. Twenty subjects performed BFR resistance training (BFR group), and the remaining 20 performed ordinary resistance training without BFR. Resistance training was performed at 20 % of each estimated one-repetition maximum for 4 weeks. We measured lactate (Lac), norepinephrine (NE), vascular endothelial growth factor (VEGF) and growth hormone (GH) before and after the initial resistance training. The reactive hyperemia index (RHI), von Willebrand factor (vWF) and transcutaneous oxygen pressure in the foot (Foot-tcPO2) were assessed before and after the 4-week resistance training period.

RESULTS

Lac, NE, VEGF and GH increased significantly from 8.2 ± 3.6 mg/dL, 619.5 ± 243.7 pg/mL, 43.3 ± 15.9 pg/mL and 0.9 ± 0.7 ng/mL to 49.2 ± 16.1 mg/dL, 960.2 ± 373.7 pg/mL, 61.6 ± 19.5 pg/mL and 3.1 ± 1.3 ng/mL, respectively, in the BFR group (each P < 0.01). RHI and Foot-tcPO2 increased significantly from 1.8 ± 0.2 and 62.4 ± 5.3 mmHg to 2.1 ± 0.3 and 68.9 ± 5.8 mmHg, respectively, in the BFR group (each P < 0.01). VWF decreased significantly from 175.7 ± 20.3 to 156.3 ± 38.1 % in the BFR group (P < 0.05).

CONCLUSIONS

BFR resistance training improved vascular endothelial function and peripheral blood circulation in healthy elderly people.

Endothelium Expression of Bcl-2 Is Essential for Normal and Pathological Ocular Vascularization

Bcl-2 is an anti-apoptotic protein with important roles in vascular homeostasis and angiogenesis. Mice globally lacking Bcl-2 (Bcl-2 -/-) are small in stature and succumb to renal failure shortly after weaning as a result of renal hypoplasia/cystic dysplasia. We have shown that Bcl-2 -/- mice displayed attenuated retinal vascular development and neovascularization. In vitro studies indicated that in addition to modulating apoptosis, Bcl-2 expression also impacts endothelial and epithelial cell adhesion, migration and extracellular matrix production. However, studies delineating the cell autonomous role Bcl-2 expression plays in the endothelium during vascular development, pruning and remodeling, and neovascularization are lacking. Here we generated mice carrying a conditional Bcl-2 allele (Bcl-2Flox/Flox) and VE-cadherin-cre (Bcl-2EC mice). Bcl-2EC mice were of normal stature and lifespan and displayed some but not all of the retinal vascular defects previously observed in global Bcl-2 deficient mice. Bcl-2EC mice had decreased numbers of endothelial cells, decreased retinal arteries and premature primary branching of the retinal vasculature, but unlike the global knockout mice, spreading of the retinal superficial vascular layer proceeded normally. Choroidal neovascularization was attenuated in Bcl-2EC mice, although retinal neovascularization accompanying oxygen-induced ischemic retinopathy was not. Thus, Bcl-2 expression in the endothelium plays a significant role during postnatal retinal vascularization, and pathological choroidal but not retinal neovascularization, suggesting vascular bed specific Bcl-2 function in the endothelium.

Estradiol mediates vasculoprotection via ERRα-dependent regulation of lipid and ROS metabolism in the endothelium

The estrogen-mediated vasculoprotective effect has been widely reported in many animal studies, although the clinical trials are controversial and the detailed mechanisms remain unclear. In this study, we focused on the molecular mechanism and consequence of 17β-estradiol (E2)-induced ERRα (estrogen-related receptor alpha) expression in endothelium and its potential beneficial effects on vascular function. The human aorta endothelial cells were used to identify the detailed molecular mechanism and consequences for E2-induced ERRα expression through estrogen receptors (ER), where ERα responses E2-induced ERRα activation, and ERβ responses basal ERRα expression. E2-induced ERRα expression increases fatty acid uptake/oxidation with increased mitochondrial replication, ATP generation and attenuated reactive oxygen species (ROS) formation. We have obtained further in vivo proof from high-fat diet mice that the lentivirus-carried endothelium-specific delivery of ERRα expression on the vascular wall normalizes E2 deficiency-induced increased plasma lipids with ameliorated vascular damage. ERRα knockdown worsens the problem, and the E2 could only partly restore this effect. This is the first time we report the detailed mechanism with direct evidence that E2-induced ERRα expression modulates the fatty acid metabolism and reduces the circulating lipids through endothelium. We conclude that E2-induced ERRα expression in endothelium plays an important role for the E2-induced vasculoprotective effect.

[THE EFFECT OF PERINATAL HYPOXIA ON THE STRUCTURE OF BLOOD-BRAIN BARRIER IN RATS TREATED WITH SALIFEN]

The work was performed on Wistar rats, which were dividedinto 3 groups: 1st group--experimental rats subjected to hypoxia and treated with salifen (15 mg/kg for 14 days), 2nd group--control rats exposed to hypoxia only without treatment, and 3rdgroup--intact animals (8-10 animals in each group). Using themethods of light and electron microscopy, the effect of salifen onthe structural characteristics of the elements of the blood-brainbarrier (BBB) in the neocortex was studied in rats after exposureto hypoxia in the early postnatal period--on postnatal Day 2(model of human preterm pregnancy). The results showed thatsalifen had a positive effect on the state of the microvasculatureafter perinatal hypoxia, in particular, on the state of endothelialcells. Its active participation in the compensatory-adaptive reactions of the BBB in response to hypoxia exposure was detected,and the prospects of further studies of the protective properties ofsalifen are emphasized.

Nuclear receptor subfamily 2 group F member 1a (nr2f1a) is required for vascular development in zebrafish

Genetic regulators and signaling pathways are important for the formation of blood vessels. Transcription factors controlling vein identity, intersegmental vessels (ISV) growth and caudal vein plexus (CVP) formation in zebrafish are little understood as yet. Here, we show the importance of the nuclear receptor subfamily member 1A (nr2f1a) in zebrafish vascular development. Amino acid sequence alignment and phylogenetic analysis of nr2f1a is highly conserved among the vertebrates. Our in situ hybridization results showed nr2f1a mRNA is expressed in the lateral plate mesoderm at 18 somite stage and in vessels at 24-30 hpf, suggesting its roles in vasculization. Consistent with this morpholino-based knockdown of nr2fla impaired ISV growth and failed to develop fenestrated vascular structure in CVP, suggesting that nr2f1a has important roles in controlling ISV and CVP growth. Consequently, nr2f1a morphants showed pericardial edema and circulation defects. We further demonstrated reduced ISV cells and decreased CVP endothelial cells sprouting in nr2f1a morphants, indicating the growth impairment of ISV and CVP is due to a decrease of cell proliferation and migration, but not results from cell death in endothelial cells after morpholino knockdown. To test molecular mechanisms and signals that are associated with nr2f1a, we examined the expression of vascular markers. We found that a loss of nr2f1a results in a decreased expression of vein/ISV specific markers, flt4, mrc1, vascular markers stabilin and ephrinb2. This indicates the regulatory role of nr2f1a in controlling vascular development. We further showed that nr2f1a likely interact with Notch signaling by examining nr2f1a expression in rbpsuh morphants and DAPT-treatment embryos. Together, we show nr2f1a plays a critical role for vascular development in zebrafish.

Engineering interconnected 3D vascular networks in hydrogels using molded sodium alginate lattice as the sacrificial template

Engineering 3D perfusable vascular networks in vitro and reproducing the physiological environment of blood vessels is very challenging for tissue engineering and investigation of blood vessel function. Here, we engineer interconnected 3D microfluidic vascular networks in hydrogels using molded sodium alginate lattice as sacrificial templates. The sacrificial templates are rapidly replicated in polydimethylsiloxane (PDMS) microfluidic chips via Ca⁺²-crosslinking and then fully encapsulated in hydrogels. Interconnected channels with well controlled size and morphology are obtained by dissolving the monolayer or multilayer templates with EDTA solution. The human umbilical vein endothelial cells (HUVECs) are cultured on the channel linings and proliferated to form vascular lumens. The strong cell adhesion capability and adaptive response to shear stress demonstrate the excellent cytocompatibility of both the template and template-sacrificing process. Furthermore, the barrier function of the endothelial layer is characterized and the results show that a confluent endothelial monolayer is fully developed. Taken together, we develop a facile and rapid approach to engineer a vascular model that could be potentially used in physiological studies of vascular functions and vascular tissue engineering.

Progenitor endothelial cell involvement in Alzheimer's disease

There is compelling evidence that endothelial cells of the brain and periphery are dysfunctional in Alzheimer's disease. There is evidence for a fundamental defect in, or abnormal aging of, endothelial progenitor cells in atherosclerosis. The possibility that endothelial cell defects are a primary cause for Alzheimer's disease or other dementias can be researched by molecular and cell biology studies as well as cell trafficking studies using recently demonstrated molecular imaging methods. The evidence for abnormal endothelial function and the methods to explore this hypothesis are presented.

Enhancing microvascular formation and vessel maturation through temporal control over multiple pro-angiogenic and pro-maturation factors

Therapeutic stimulation of angiogenesis to re-establish blood flow in ischemic tissues offers great promise as a treatment for patients suffering from cardiovascular disease or trauma. Since angiogenesis is a complex, multi-step process, different signals may need to be delivered at appropriate times in order to promote a robust and mature vasculature. The effects of temporally regulated presentation of pro-angiogenic and pro-maturation factors were investigated in vitro and in vivo in this study. Pro-angiogenic factors vascular endothelial growth factor (VEGF) and angiopoietin 2 (Ang2) cooperatively promoted endothelial sprouting and pericyte detachment in a three-dimensional in vitro EC-pericyte co-culture model. Pro-maturation factors platelet-derived growth factor B (PDGF) and angiopoietin 1 (Ang1) inhibited the early stages of VEGF- and Ang2-mediated angiogenesis if present simultaneously with VEGF and Ang2, but promoted these behaviors if added subsequently to the pro-angiogenesis factors. VEGF and Ang2 were also found to additively enhance microvessel density in a subcutaneous model of blood vessel formation, while simultaneously administered PDGF/Ang1 inhibited microvessel formation. However, a temporally controlled scaffold that released PDGF and Ang1 at a delay relative to VEGF/Ang2 promoted both vessel maturation and vascular remodeling without inhibiting sprouting angiogenesis. Our results demonstrate the importance of temporal control over signaling in promoting vascular growth, vessel maturation and vascular remodeling. Delivering multiple growth factors in combination and sequence could aid in creating tissue engineered constructs and therapies aimed at promoting healing after acute wounds and in chronic conditions such as diabetic ulcers and peripheral artery disease.

Interaction between pericytes and endothelial cells leads to formation of tight junction in hyaloid vessels

The hyaloid vessel is a transient vascular network that nourishes the lens and the primary vitreous in the early developmental periods. In hyaloid vessels devoid of the support of astrocytes, we demonstrate that tight junction proteins, zonula occludens-1 and occludin, are regularly expressed at the junction of endothelial cells. To figure out the factor influencing the formation of tight junctions in hyaloid vessels, we further progress to investigate the interactions between endothelial cells and pericytes, two representative constituent cells in hyaloid vessels. Interestingly, endothelial cells interact with pericytes in the early postnatal periods and the interaction between two cell types provokes the up-regulation of transforming growth factor β1. Further in vitro experiments demonstrate that transforming growth factor β1 induces the activation of Smad2 and Smad3 and the formation of tight junction proteins. Taken together, in hyaloid vessels, pericytes seem to regulate the formation of tight junctions by the interaction with endothelial cells even without the support of astrocytes. Additionally, we suggest that the hyaloid vessel is a valuable system that can be utilized for the investigation of cell-cell interaction in the formation of tight junctions in developing vasculatures.

Pericytes in development and pathology of skeletal muscle

Increasing attention is currently devoted to the multiple roles that pericytes (also defined as mural, Rouget, or perivascular cells) may play during angiogenesis, vascular homeostasis, and pathology. Many recent excellent reviews thoroughly address these topics (see below); hence, we will not discuss them in detail here. However, not much is known about origin, heterogeneity, gene expression, and developmental potential of pericytes during fetal and postnatal development. This is likely because of the paucity of markers expressed by pericytes and the absence of truly unique ones. Thus, in vivo identification and ex perspective isolation are challenging and explain the relative little data available in comparison with neighbor but far more characterized cells such as the endothelium. Despite this preliminary knowledge, we will propose that contribution to growing mesoderm tissues may be an important role for pericytes. Thus, their ability to contribute to tissue regeneration may be a consequence of their role in tissue growth. However, in a severely damaged or diseased tissue, acute or chronic inflammation likely results in the production of signaling molecules that are different from those present in developing tissues, thus explaining why pericytes are easily diverted from a regenerative to a fibrotic fate.

Norrin expression in endothelial cells in the developing mouse retina

Norrin, a protein that acts on Frizzled-4 receptor, participates in angiogenesis in a variety of contexts through the Wnt-signaling pathway. Specifically, Norrin is found to play a crucial role in retinal vascularization. Norrin's pivotal role in angiogenesis led us to investigate its expression and the primary source in the developing retina. In this study we demonstrate, for the first time, that Norrin protein is expressed along the retinal blood vessels. The expression of Norrin coincided with the pattern of vascular growth in the developing mouse retina, and its expression was identified from the endothelial cells of the retinal capillaries. Furthermore, Norrin was also expressed on endothelial cells of the developing human retina. Given that Norrin is crucial in the normal development and maintenance of ocular capillaries, our finding provides a hint of the involvement of Norrin in the self generative and protective mechanism of the endothelial cells in the developing retina.

Evolutionary origins of the blood vascular system and endothelium

Every biological trait requires both a proximate and evolutionary explanation. The field of vascular biology is focused primarily on proximate mechanisms in health and disease. Comparatively little attention has been given to the evolutionary basis of the cardiovascular system. Here, we employ a comparative approach to review the phylogenetic history of the blood vascular system and endothelium. In addition to drawing on the published literature, we provide primary ultrastructural data related to the lobster, earthworm, amphioxus, and hagfish. Existing evidence suggests that the blood vascular system first appeared in an ancestor of the triploblasts over 600 million years ago, as a means to overcome the time-distance constraints of diffusion. The endothelium evolved in an ancestral vertebrate some 540-510 million years ago to optimize flow dynamics and barrier function, and/or to localize immune and coagulation functions. Finally, we emphasize that endothelial heterogeneity evolved as a core feature of the endothelium from the outset, reflecting its role in meeting the diverse needs of body tissues.

Mutant-specific gene expression profiling identifies SRY-related HMG box 11b (SOX11b) as a novel regulator of vascular development in zebrafish

Previous studies have identified two zebrafish mutants, cloche and groom of cloche, which lack the majority of the endothelial lineage at early developmental stages. However, at later stages, these avascular mutant embryos generate rudimentary vessels, indicating that they retain the ability to generate endothelial cells despite this initial lack of endothelial progenitors. To further investigate molecular mechanisms that allow the emergence of the endothelial lineage in these avascular mutant embryos, we analyzed the gene expression profile using microarray analysis on isolated endothelial cells. We find that the expression of the genes characteristic of the mesodermal lineages are substantially elevated in the kdrl (+) cells isolated from avascular mutant embryos. Subsequent validation and analyses of the microarray data identifies Sox11b, a zebrafish ortholog of SRY-related HMG box 11 (SOX11), which have not previously implicated in vascular development. We further define the function sox11b during vascular development, and find that Sox11b function is essential for developmental angiogenesis in zebrafish embryos, specifically regulating sprouting angiogenesis. Taken together, our analyses illustrate a complex regulation of endothelial specification and differentiation during vertebrate development.

Long-term results of tissue-engineered small-caliber vascular grafts in a rat carotid arterial replacement model

The concept of tissue engineered small-caliber vascular grafts (TE-SCVGs) is theoretically ideal. In this study, we evaluated the long-term (more than 1 year) course of TE-SCVGs using a rat carotid arterial replacement model. We fabricated a TE-SCVG scaffold (0.7 mm in diameter) with electrospun nano-scale fibers. Poly-ε-caprolactone was used as a biodegradable polymer. These artificial vessels were then used in carotid arterial replacement performed on Sprague-Dawley rats. The implanted grafts were removed at an early phase (1, 2, 6 weeks), middle phase (12, 24 weeks), and late phase (48, 72 weeks) after implantation. Twenty-nine patent grafts from among the 40 implanted grafts (patency 72.5 %) could be evaluated. No aneurysm formation was observed during the follow-up period. Endothelial cells positive for immunostaining with von Willebrand factor were found to be already attached to the inner surface of the TE-SCVGs in the early phase. The percentage of smooth muscle cell specific marker (α-smooth muscle actin and calponin with fluorescent immunostaining) positive cells, which seemed to be mesenchymal cells in the graft wall, increased with time, while, in contrast, the scaffold material decreased. Even after 72 weeks, however, although the scaffold material had degraded, it had not disappeared completely. These results show that the novel TE-SCVGs we developed were still functioning in the rat carotid arterial circulation after more than 1 year. However, further investigations will be required with regard to regeneration of the SMC layer and the complete degradation of graft materials.

Thromboresistant and endothelialization effects of dopamine-mediated heparin coating on a stent material surface

Heparinization of surfaces has proven a successful strategy to prevent thrombus formation. Inspired by the composition of adhesive proteins in mussels, the authors used dopamine to immobilize heparin on a stent surface. This study aimed to assess the thromboresistant and endothelialization effects of dopamine-mediated heparin (HPM) coating on a stent material surface. The HPM was synthesized by bonding dopamine and heparin chemically. Cobalt-chromium (Co-Cr) alloy disks were first placed in the HPM solution and applied to surface stability then underwent thromboresistant tests and human umbilical vein endothelial cells (HUVEC) cytotoxicity assays. The results showed not only thromboresistant activity and a stable state of heparin on the surfaces after investigation with toluidine blue and thrombin activation assay but also proliferation of HUVEC in vitro. Studies on animals showed that the HPM-coated stent has no obvious inflammation response and increasing of restenosis rate compared to the bare metal stent (BMS) indicating good biocompatibility as well as safety in its in vivo application. Moreover, improving the endothelial cell (EC) proliferation resulted in a higher strut-covering rate (i.e., endothelialization) with shuttle-shaped EC in the HPM-coated stent group compared to that of the BMS group. These results suggest that this facile coating approach could significantly promote endothelialization and offer greater safety than the BMS for its much improved thromboresistant property. Moreover, it may offer a platform for conjugating secondary drugs such as anti-proliferative drugs.

Angiotensin II modulates VEGF-driven angiogenesis by opposing effects of type 1 and type 2 receptor stimulation in the microvascular endothelium

Vascular endothelial growth factor (VEGF) is a main stimulator of pathological vessel formation. Nevertheless, increasing evidence suggests that Angiotensin II (Ang II) can play an augmentory role in this process. We thus analyzed the contribution of the two Ang II receptor types, AT(1)R and AT(2)R, in a mouse model of VEGF-driven angiogenesis, i.e. oxygen-induced proliferative retinopathy. Application of the AT(1)R antagonist telmisartan but not the AT(2)R antagonist PD123,319 largely attenuated the pathological response. A direct effect of Ang II on endothelial cells (EC) was analyzed by assessing angiogenic responses in primary bovine retinal and immortalized rat microvascular EC. Selective stimulation of the AT(1)R by Ang II in the presence of PD123,319 revealed a pro-angiogenic activity which further increased VEGF-driven EC sprouting and migration. In contrast, selective stimulation of the AT(2)R by either CGP42112A or Ang II in the presence of telmisartan inhibited the VEGF-driven angiogenic response. Using specific inhibitors (pertussis toxin, RGS proteins, kinase inhibitors) we identified G(12/13) and G(i) dependent signaling pathways as the mediators of the AT(1)R-induced angiogenesis and the AT(2)R-induced inhibition, respectively. As AT(1)R and AT(2)R stimulation displays opposing effects on the activity of the monomeric GTPase RhoA and pro-angiogenic responses to Ang II and VEGF requires activation of Rho-dependent kinase (ROCK), we conclude that the opposing effects of the Ang II receptors on VEGF-driven angiogenesis converge on the regulation of activity of RhoA-ROCK-dependent EC migration.

Changes in eNOS phosphorylation contribute to increased arteriolar NO release during juvenile growth

Nitric oxide (NO) mediates a major portion of arteriolar endothelium-dependent dilation in adults, but indirect evidence has suggested that NO contributes minimally to these responses in the young. Isolated segments of arterioles were studied in vitro to verify this age-related increase in NO release and investigate the mechanism by which it occurs. Directly measured NO release induced by ACh or the Ca(2+) ionophore A-23187 was five- to sixfold higher in gracilis muscle arterioles from 42- to 46-day-old (juvenile) rats than in those from 25- to 28-day-old (weanling) rats. There were no differences between groups in arteriolar endothelial NO synthase (eNOS) expression or tetrahydrobiopterin levels, and arteriolar l-arginine levels were lower in juvenile vessels than in weanling vessels (104 ± 6 vs.126 ± 3 pmol/mg). In contrast, agonist-induced eNOS Thr(495) dephosphorylation and eNOS Ser(1177) phosphorylation (events required for maximal activity) were up to 30% and 65% greater, respectively, in juvenile vessels. Juvenile vessels did not show increased expression of enzymes that mediate these events [protein phosphatases 1 and 2A and PKA and PKB (Akt)] or heat shock protein 90, which facilitates Ser(1177) phosphorylation. However, agonist-induced colocalization of heat shock protein 90 with eNOS was 34-66% greater in juvenile vessels than in weanling vessels, and abolition of this difference with geldanamycin also abolished the difference in Ser(1177) phosphorylation between groups. These findings suggest that growth-related increases in arteriolar NO bioavailability may be due at least partially to changes in the regulation of eNOS phosphorylation and increased signaling activity, with no change in the abundance of eNOS signaling proteins.

Mechanisms of vascular endothelial growth factor-induced pathfinding by endothelial sprouts in biomaterials

A critical property of biomaterials for use in regenerative medicine applications is the ability to promote angiogenesis, the formation of new vascular networks, to support regenerating tissues. Recent studies have demonstrated that a complex interplay exists between biomechanical and biochemical regulators of endothelial cell sprouting, an early step in angiogenesis. Here, we use a microfluidic platform to study the pathfinding behaviors induced by various stable vascular endothelial growth factor (VEGF) gradients during sprouting morphogenesis within biomaterials. Quantitative, time-lapse analysis of endothelial sprouting demonstrated that the ability of VEGF to regulate sprout orientation during several stages of sprouting morphogenesis (initiation, elongation, and turning navigation) was biomaterial dependent. Identical VEGF gradients induced different types of coordinated cell movements depending on the density of the surrounding collagen/fibronectin matrix. In denser matrices, sprouts were more likely to have an initial orientation aligned parallel to the VEGF gradient. In contrast, in less dense matrices, sprouts were more likely to initially misalign with the VEGF gradient; however, these sprouts underwent significant turning and navigation to eventually reorient to be parallel to the VEGF gradient. These less dense matrices required shallower VEGF gradients and demonstrated lower activating VEGF thresholds to induce proper sprout alignment and pathfinding. These results encourage the future use of microfluidic platforms to probe fundamental aspects of matrix effects on angiogenesis, to screen biomaterials for angiogenic potential, and to design ex vivo tissues with aligned vascular networks.

Identification of a monocyte-predisposed hierarchy of hematopoietic progenitor cells in the adventitia of postnatal murine aorta

BACKGROUND

Hematopoiesis originates from the dorsal aorta during embryogenesis. Although adult blood vessels harbor progenitor populations for endothelial and smooth muscle cells, it is not known if they contain hematopoietic progenitor or stem cells. Here, we hypothesized that the arterial wall is a source of hematopoietic progenitor and stem cells in postnatal life.

METHODS AND RESULTS

Single-cell aortic disaggregates were prepared from adult chow-fed C57BL/6 and apolipoprotein E-null (ApoE(-/-)) mice. In short- and long-term methylcellulose-based culture, aortic cells generated a broad spectrum of multipotent and lineage-specific hematopoietic colony-forming units, with a preponderance of macrophage colony-forming units. This clonogenicity was higher in lesion-free ApoE(-/-) mice and localized primarily to stem cell antigen-1-positive cells in the adventitia. Expression of stem cell antigen-1 in the aorta colocalized with canonical hematopoietic stem cell markers, as well as CD45 and mature leukocyte antigens. Adoptive transfer of labeled aortic cells from green fluorescent protein transgenic donors to irradiated C57BL/6 recipients confirmed the content of rare hematopoietic stem cells (1 per 4 000 000 cells) capable of self-renewal and durable, low-level reconstitution of leukocytes. Moreover, the predominance of long-term macrophage precursors was evident by late recovery of green fluorescent protein-positive colonies from recipient bone marrow and spleen that were exclusively macrophage colony-forming units. Although trafficking from bone marrow was shown to replenish some of the hematopoietic potential of the aorta after irradiation, the majority of macrophage precursors appeared to arise locally, suggesting long-term residence in the vessel wall.

CONCLUSIONS

The postnatal murine aorta contains rare multipotent hematopoietic progenitor/stem cells and is selectively enriched with stem cell antigen-1-positive monocyte/macrophage precursors. These populations may represent novel, local vascular sources of inflammatory cells.

Wnt signaling mediates pathological vascular growth in proliferative retinopathy

BACKGROUND

Ischemic proliferative retinopathy, characterized by pathological retinal neovascularization, is a major cause of blindness in working-age adults and children. Defining the molecular pathways distinguishing pathological neovascularization from normal vessels is critical to controlling these blinding diseases with targeted therapy. Because mutations in Wnt signaling cause defective retinal vasculature in humans with some characteristics of the pathological vessels in retinopathy, we investigated the potential role of Wnt signaling in pathological retinal vascular growth in proliferative retinopathy.

METHODS AND RESULTS

In this study, we show that Wnt receptors (Frizzled4 and low-density lipoprotein receptor-related protein5 [Lrp5]) and activity are significantly increased in pathological neovascularization in a mouse model of oxygen-induced proliferative retinopathy. Loss of Wnt coreceptor Lrp5 and downstream signaling molecule dishevelled2 significantly decreases the formation of pathological retinal neovascularization in retinopathy. Loss of Lrp5 also affects retinal angiogenesis during development and formation of the blood-retinal barrier, which is linked to significant downregulation of tight junction protein claudin5 in Lrp5(-/-) vessels. Blocking claudin5 significantly suppresses Wnt pathway-driven endothelial cell sprouting in vitro and developmental and pathological vascular growth in retinopathy in vivo.

CONCLUSIONS

These results demonstrate an important role of Wnt signaling in pathological vascular development in retinopathy and show a novel function of Cln5 in promoting angiogenesis.

Endothelium-dependent control of vascular tone during early postnatal and juvenile growth

Endothelial dysfunction can develop at an early age in children with risk factors for cardiovascular disease. A clear understanding of the nature of this dysfunction and how it can worsen over time requires detailed information on the normal growth-related changes in endothelial function on which the pathological changes are superimposed. This review summarizes our current understanding of these normal changes, as derived from studies in four different mammalian species. Although the endothelium plays an important role in controlling vascular tone from birth onward, the vasoactive molecules that mediate this control often change during postnatal or juvenile growth. The specifics of this transition to an adult endothelial cell phenotype can vary depending on the vascular bed. During growth, the contribution of nitric oxide to endothelium-dependent dilation generally increases in the lung, cerebral cortex, and skeletal muscle, but decreases in the intestine. Endothelial capacity for release of other vasoactive factors (e.g., cyclooxygenase products, hydrogen peroxide, carbon monoxide) can also increase or decrease during growth. Although these changes have been well documented, there is less information on their underlying cellular or molecular events. Further research is required to clarify these mechanisms, and to evaluate the functional significance of such shifts in endothelial phenotype.

In vitro study in the endothelial cell compatibility and endothelialization of genipin-crosslinked biological tissues for tissue-engineered vascular scaffolds

To overcome the cytotoxicity of the chemical reagents used to fix bioprostheses, genipin, a naturally occurring crosslinking agent, was used to fix biological tissues in present study. We prepared the biological vascular scaffolds through cell extraction and fixing the porcine thoracic arteries with 1% (by w/v) genipin solution for 3 days, and then examined their mechanical properties and microstructures; glutaraldehyde- and epoxy-fixed counterparts were used as controls. HUVECs were seeded on the type I collagen-coated surface of different modified acellular vascular tissues (fixed with different crosslinking agents), and the growths of HUVECs on the specimens were demonstrated by means of MTT test, the secretion of PGI2 and vWF by HUVECs on the various specimens was also measured. Finally, HUVECs were seeded on the luminal surface of acellular biological vascular scaffolds (<6 mm internal diameter) which were, respectively, treated in the same manner described above, and then cultured for 9 days. On the ninth day, the HUVECs on the luminal surface of these vascular scaffolds were examined morphologically and by immunohistochemistry. Genipin-fixation can markedly diminish antigenicity of the vascular tissues through partially getting rid of cell or reducing the level of free amino groups in the vascular tissues. Genipin-fixed acellular vascular tissues mimicked the natural vessels due to the maintenance of the integrity of total structure and the large preservation of the microstructures of collagen fibers and elastic fibers; therefore, it appeared suitable to fabricate vascular scaffolds in mechanical properties. Compared to controls, the genipin-fixed acellular vascular tissues were characterized by low cytotoxicity and good cytocompatibility. The HUVECs can not only proliferate well on the genipin-fixed acellular vascular tissues, but also preserve the activities and function of endothelial cells, and easily make it endothelialized in vitro. The results showed that the genipin-fixed acellular porcine vascular scaffolds should be promising materials for fabricating vascular grafts or the scaffolds of tissue-engineered blood vessels.

Hepatoblast and mesenchymal cell-specific gene-expression in fetal rat liver and in cultured fetal rat liver cells

The aim of this study was to determine whether passaged rat fetal liver cells are functional hepatoblasts. Hepatocyte/hepatoblast- and liver myofibroblast-gene-expressions were studied in adult and fetal rat liver tissues as well as in primary and passaged cultures of isolated rat fetal liver cells at both the mRNA and protein level. Desmin- and Alpha-Smooth Muscle Actin (SMA)-positive cells were located in the walls of liver vessels, whereas Desmin-positive/SMA-negative cells were distributed within the liver parenchyma. Primary cultures contained Prox1-positive hepatoblasts, Desmin/SMA-positive myofibroblasts and only a few Desmin-positive/SMA-negative cells. Albumin and alpha-fetoprotein (AFP) could be detected in the primary cultures and to a lesser extent after the first passage. The number of Desmin-positive/SMA-negative cells decreased with successive passage, such that after the second passage, only Desmin/SMA-positive cells could be detected. SMA-gene-expression increased during the passages, suggesting that myofibroblasts become the major cell population of fetal liver cell cultures over time. This observation needs to be taken into account, should passaged fetal liver cells be used for liver cell transplantation. Moreover it contradicts the concept of epithelial-mesenchymal transformation and suggests rather that selective overgrowth of mesenchymal cells occurs in culture.

Multiple stressors and the response of vascular endothelial cells: the effect of aging and diabetes

BACKGROUND

The present study examined the effects of local heat, global heat, and the interaction between these two endothelial stressors on the blood flow of the skin of the foot in people who are older and who have diabetes.

METHODS

Subjects who were older (mean age 64.2 +/- 5.9 years) and were younger (mean age 25.7 +/- 2.9 years) and subjects who had diabetes (mean age 62 +/- 5.9 years, mean duration 13.2 +/- 9.1 years) participated. Subjects were exposed to three global temperatures (16 degrees C, 24 degrees C, and 32 degrees C), and the blood flow response was recorded on the foot with a laser Doppler flow meter for 30 s following applications of local heat (30 degrees C, 33.5 degrees C, and 37 degrees C) using a Peltier junction to clamp the skin for 2 min.

RESULTS

All three groups significantly increased blood flow from the 16-24 degrees C environments for the 37 degrees C application of local heat (P(Younger) = 0.02, P(Older) = 0.02, P(Diabetes) = 0.01). Those with diabetes and those who were older only increased blood flow 5% and 6% from the 24-32 degrees C environment, which was not statistically significant (P(Older) = 0.12, P(Diabetes) = 0.14).

CONCLUSIONS

There appears to be considerable blood flow reserve in younger subjects to tolerate heat stress. In contrast, older subjects and those with diabetes reach a critical level after which additional heat does not cause in increase in blood flow.

An original flow diversion device for the treatment of intracranial aneurysms: evaluation in the rabbit elastase-induced model

BACKGROUND AND PURPOSE

The potential for successful treatment of intracranial aneurysms by flow diversion is gradually being recognized in the clinical setting; however, the devices currently available (stents) are not designed for flow diversion. We evaluate the long-term response of an appropriately designed flow diversion device in producing thrombotic occlusion of experimental aneurysms.

METHODS

Three different configurations of an original flow diversion device were implanted across thirty elastase-induced aneurysm models in rabbits. Ten animals per device configuration were followed-up for 3 weeks (n=3), 3 months (n=3), or 6 months (n=4), and tissue explanted postsacrifice was sent for histology. The temporal variation in angiographic contrast intensity within each aneurysm was fitted with a mathematical model to quantify the alteration in local hemodynamics caused by the implanted device. A predictive index, called the washout coefficient, was constructed to estimate long-term aneurysm occlusion probabilities immediately after treatment with any flow diversion device.

RESULTS

The device with a porosity of 70% and pore density of 18 pores/mm(2) performed better at occluding aneurysms than devices with 70% porosity, 12 pores/mm(2) and 65% porosity, 14 pores/mm(2). A value of the washout coefficient less than 30 predicted greater than 97% angiographic aneurysm occlusion over a period of 6 months with a sensitivity of 73% and specificity of 82%.

CONCLUSIONS

The flow diversion devices effected successful and stable aneurysm occlusion. Pore density, rather than porosity, may be the critical factor modulating efficacy of such devices.

Impact of blood circulation on reendothelialization, restenosis and atrovastatin's restenosis prevention effects

BACKGROUND

The independent effects of numerous circulating inflammatory cytokines and inflammatory associated blood cells on reendothelialization and restenosis after PCI has been elucidated, whereas the blood circulation's general effect on restenosis is still pending. Thereby, author investigated the impact of blood circulation on reendothelialization, restenosis and atrovastatin's restenosis prevention effects.

METHODS AND RESULTS

70 SD rats were divided equally in 7 groups: sham operation group, deendothelialization group, atrovastatin treatment group, occlusion group, occlusion and deendothelialization group, atrovastatin treatment after occlusion and deendothelialization group, and immediate sacrifice (after deendothelialization) group. The carotid model of deendothelialization by balloon and (or) thromboembolism occlusion was established, and 4 weeks after balloon injury, the reendothelialization ratio and restenosis ratio of each subjects were observed. The outcomes revealed that there is a natural self-repair phenomenon, featured as low level reendothelialization and restenosis inhibition, which can be significantly augmented under atrovastatin treatment. Yet when the blood circulation discontinued, not only the self-repair process, but also atrovastatin's beneficial effects on reendothelialization and restenosis disappeared. SPSS analysis revealed that there was inverse correlation between reendothelialization and restenosis.

CONCLUSIONS

Blood circulation not only per se generally promote reendothelialization and inhibits restenosis, but also serves as a necessary pathway for atrovastatin exerting therapeutic effects on reendothelialization and restenosis; Accelerating reendothelialization is a promising approach of restenosis prevention.

Aminopeptidase O contains a functional nucleolar localization signal and is implicated in vascular biology

We have identified a gene trap integration into Aminopeptidase O, the gene encoding a member of the M1 family of metalloproteases. Using the betagal reporter of the gene trap vector, we have revealed that at least some ApO isoforms are expressed predominantly in embryonic and adult blood vessels leading us to propose that ApO plays a role in vascular cell biology. The protein produced from an engineered Gfp-ApO fusion cDNA localises to the nucleolus in transfected COS7 cells. We confirm that indeed the APO protein contains a functional nucleolar localisation domain by demonstrating that GFP-APO fusion proteins that lack the predicted nucleolar localisation signal are retained in the cytoplasm. We report the existence of multiple alternatively spliced Apo isoforms that differ with respect to the presence of exons encoding important functional domains. Alternative splicing predictably produces protein products with or without the catalytic domain and/or a nucleolar localisation signal and therefore likely represents an important mechanism in regulating the biological activity of APO that has been reported to cleave one of the peptides of the renin angiotensin pathway.

HOXA13 Is essential for placental vascular patterning and labyrinth endothelial specification

In eutherian mammals, embryonic growth and survival is dependent on the formation of the placenta, an organ that facilitates the efficient exchange of oxygen, nutrients, and metabolic waste between the maternal and fetal blood supplies. Key to the placenta's function is the formation of its vascular labyrinth, a series of finely branched vessels whose molecular ontogeny remains largely undefined. In this report, we demonstrate that HOXA13 plays an essential role in labyrinth vessel formation. In the absence of HOXA13 function, placental endothelial cell morphology is altered, causing a loss in vessel wall integrity, edema of the embryonic blood vessels, and mid-gestational lethality. Microarray analysis of wild-type and mutant placentas revealed significant changes in endothelial gene expression profiles. Notably, pro-vascular genes, including Tie2 and Foxf1, exhibited reduced expression in the mutant endothelia, which also exhibited elevated expression of genes normally expressed in lymphatic or sinusoidal endothelia. ChIP analysis of HOXA13–DNA complexes in the placenta confirmed that HOXA13 binds the Tie2 and Foxf1 promoters in vivo. In vitro, HOXA13 binds sequences present in the Tie2 and Foxf1 promoters with high affinity (K_d = 27–42 nM) and HOXA13 can use these bound promoter regions to direct gene expression. Taken together, these findings demonstrate that HOXA13 directly regulates Tie2 and Foxf1 in the placental labyrinth endothelia, providing a functional explanation for the mid-gestational lethality exhibited by Hoxa13 mutant embryos as well as a novel transcriptional program necessary for the specification of the labyrinth vascular endothelia.

Defects in placental development are a common cause of mid-gestational lethality. Key to the placenta's function is its vascular labyrinth, a series of finely branched vessels that facilitate the efficient exchange of gases, nutrients, and metabolic waste between the maternal and fetal blood supplies. In this study, we identify a novel role for the transcription factor HOXA13 in formation of the placental vascular labyrinth. In the absence of HOXA13 function, labyrinth vessel branching and endothelial specification is compromised, causing mid-gestational lethality due to placental insufficiency. Analysis of the genes affected by the loss of HOXA13 function revealed significant reductions in the expression of several pro-vascular genes, including Tie2 and Foxf1. Analysis of the Tie2 and Foxf1 promoters confirmed that HOXA13 binds sites present in each promoter with high affinity in the placenta, and in vitro, HOXA13 can use these bound sequences to regulate gene expression. These results suggest that Tie2 and Foxf1 are direct transcriptional targets of HOXA13 in the developing placental labyrinth, providing a novel transcriptional pathway to consider when examining pathologies of the placenta and placental insufficiency, as well as the evolutionary mechanisms required for the emergence of the vascular placenta in eutherian mammals.

Hydrogen peroxide emerges as a regulator of tone in skeletal muscle arterioles during juvenile growth

OBJECTIVE

The endothelium-dependent dilation of skeletal muscle arterioles is mediated by factors that have not been identified in young rats, and partly mediated by an unidentified hyperpolarizing factor in maturing rats. This study was designed to determine if endogenous hydrogen peroxide (H2O2) contributes to this arteriolar dilation at either of these growth stages.

METHODS

Gracilis muscle arterioles were isolated from rats at ages 24-26 days ("weanlings") and 46-48 days ("juveniles"). We investigated the effects of catalase treatment on the endothelium-dependent dilation of these vessels to simvastatin and acetylcholine (ACh). Catalase-sensitive 2',7'-dichlorofluorescein (DCF) fluorescence also was measured as an index of H2O2 formation, and arteriolar dilation to exogenous H2O2 was pharmacologically probed in each age group.

RESULTS

Responses to simvastatin and ACh were attenuated by catalase in juvenile, but not weanling, arterioles. Juvenile, but not weanling, arterioles also displayed catalase-sensitive DCF fluorescence that was increased by ACh. Exogenous H2O2 could induce dilation in juvenile, but not weanling, arterioles. In juvenile arterioles, this dilation was abolished by the K+ channel inhibitors TEA and glibenclamide, and attenuated by NOS inhibition or endothelial removal.

CONCLUSIONS

These findings suggest that endogenous H2O2 contributes to endothelium-dependent arteriolar dilation in juvenile rats, but not in younger rats, and that H2O2 acts in juvenile rats by stimulating endothelial NO release and activating smooth muscle K+ channels.

In vitro cultured progenitors and precursors of cardiac cell lineages from human normal and post-ischemic hearts

The demonstration of the presence of dividing primitive cells in damaged hearts has sparked increased interest about myocardium regenerative processes. We examined the rate and the differentiation of in vitro cultured resident cardiac primitive cells obtained from pathological and normal human hearts in order to evaluate the activation of progenitors and precursors of cardiac cell lineages in post-ischemic human hearts. The precursors and progenitors of cardiomyocyte, smooth muscle and endothelial lineage were identified by immunocytochemistry and the expression of characteristic markers was studied by western blot and RT-PCR. The amount of proteins characteristic for cardiac cells (alpha-SA and MHC, VEGFR-2 and FVIII, SMA for the precursors of cardiomyocytes, endothelial and smooth muscle cells, respectively) inclines toward an increase in both alpha-SA and MHC. The increased levels of FVIII and VEGFR2 are statistically significant, suggesting an important re-activation of neoangiogenesis. At the same time, the augmented expression of mRNA for Nkx 2.5, the trascriptional factor for cardiomyocyte differentiation, confirms the persistence of differentiative processes in terminally injured hearts. Our study would appear to confirm the activation of human heart regeneration potential in pathological conditions and the ability of its primitive cells to maintain their proliferative capability in vitro. The cardiac cell isolation method we used could be useful in the future for studying modifications to the microenvironment that positively influence cardiac primitive cell differentiation or inhibit, or retard, the pathological remodeling and functional degradation of the heart.

Identification of a novel role of T cells in postnatal vasculogenesis: characterization of endothelial progenitor cell colonies

BACKGROUND

The colony number of early endothelial progenitor cells (EPCs) has been used as a quantitative indicator of the number of EPCs in the blood or as a biological marker of cardiovascular diseases. In the present study, we found a subset of T cells that were localized at the center of the EPC colony and played a pivotal role in colony formation and differentiation of early EPCs.

METHODS AND RESULTS

We found that CD3+ CD31+ CXCR4+ T cells (referred to as angiogenic T cells in the present study) constituted the center of EPC colonies during cultures of human peripheral blood mononuclear cells. These angiogenic T cells were required for colony formation and differentiation of early EPCs. They secreted high levels of angiogenic cytokines such as vascular endothelial growth factor, interleukin-8, and matrix metalloproteinases. Angiogenic T cells showed superior angiogenic potential to the other subset of T cells in the experiments with regard to Matrigel tube formation, adhesion, transendothelial migration, and collagen invasion assay, mainly through the stromal cell-derived factor 1/CXCR-4 axis. Furthermore, angiogenic T cells enhanced endothelial cell proliferation and function. In vivo study showed that angiogenic T cells play an important role in the process of vessel formation. Clinical study showed that the level of angiogenic T cells in the peripheral blood was well correlated with EPC colony numbers and had inverse relationships with age and the number of risk factors for coronary artery disease.

CONCLUSIONS

These findings suggest that angiogenic T cells could be a potential therapeutic target for ischemic cardiovascular diseases.

In vitro angiogenesis properties of endothelial progenitor cells: a promising tool for vascularization of ex vivo engineered tissues

Survival of ex vivo constructed tissues after transplantation is limited by insufficient oxygen and nutrient supply. Therefore, strategies aiming at the improvement of neovascularization of engineered tissues are a key issue. A method to enhance graft vascularization is to establish a primitive vascular plexus within the graft before transplantation by the use of cellular-based concepts. To explore the utility of endothelial progenitor cells (EPCs) for the ex vivo vascularization of tissue engineered grafts, we analyzed the in vitro angiogenic properties of this cell type in two different angiogenesis models: the 3-dimensional spheroid sprouting assay and the 2-dimensional matrigel assay. In both assays, EPCs were able to form tubelike structures, resembling early capillaries. This process was significantly enhanced by the addition of angiogenic growth factors. Direct comparison between EPCs and mature endothelial cells, represented by human umbilical vein endothelial cells (HUVECs), revealed that both cell types displayed an almost identical angiogenic potential. Other functional in vitro parameters such as angiogenic growth factor induced cell proliferation and cell survival were investigated as well, revealing a significantly decreased level of apoptosis of EPCs in relation to HUVECs under serum-deprived conditions. The observed survival advantage of EPCs along with the observation that EPCs perform very well in the above mentioned in vitro angiogenesis assays, make them an ideal autologous cell source for vascularization of ex vivo generated tissues. The attractiveness of this cell type for tissue engineering applications is strengthened further by the fact that these cells can be easily isolated from the peripheral blood of patients, thereby eliminating donor site morbidity.

Tissue-engineered vascular grafts as in vitro blood vessel mimics for the evaluation of endothelialization of intravascular devices

The accelerating use of minimally invasive procedures for the treatment of cardiovascular disease, and the commensurate development of intravascular devices such as stents, has lead to a high demand for preclinical assessment techniques. A 3-dimensional in vitro blood vessel mimic (BVM) would be ideal for device testing before animal or clinical studies. This is possible based on current capabilities for the creation of tissue-engineered vascular grafts (TEVGs). Using an established method of pressure-sodding human endothelial cells onto a polymer scaffold, a BVM was created in an in vitro bioreactor system under flow. Scanning electron microscopy and immunohistochemistry verified a cellular lining and revealed a luminal monolayer of endothelial cells. After BVM development, bare metal stents were deployed. Stented and unstented BVMs were evaluated using fluorescent nuclear staining and optical coherence tomography (OCT). En face and cross-sectional evaluation of bisbenzimide-stained nuclei revealed cellular coverage of the stent surfaces. Cross-sectional evaluation using OCT also illustrated a cellular layer developing over the stent struts. These data support the use of TEVGs as in vitro BVMs for pre-clinical evaluation of the endothelial cell response to stents and endovascular devices.

The use of mild trypsinization conditions in the detachment of endothelial cells to promote subsequent endothelialization on synthetic surfaces

A necessary condition for endothelialization of small diameter grafts is rapid and firm adhesion of endothelial cells upon exposure to flow. To retain integrins on the cell surface, we assessed the effects of trypsin concentration, the duration of trypsin incubation, and trypsin neutralization methods on endothelial cell adhesion. Human umbilical vein endothelial cells which were detached using 0.025% trypsin for 5 min and seeded onto glass pretreated with fibronectin had close to 100% cell retention when shear stresses as high as 200 dyn/cm2 were applied for 2 min. An equivalent level of cell retention was observed on fibronectin coated Teflon-AF for shear stresses up to 60 dyn/cm2 applied for 4h. Using 0.025% trypsin, initial cell spreading and cell surface alpha5beta1 integrins were increased relative to cells treated with 0.5% trypsin. After 1h of attachment, focal adhesions formed when low trypsin concentrations were used but were less evident with high trypsin concentrations. These results showed that low trypsin concentrations produced faster spreading, a higher number of intact integrins, and rapid focal adhesion formation.

Crosstalk between neovessels and mural cells directs the site-specific expression of MT1-MMP to endothelial tip cells

The membrane-anchored matrix metalloproteinase MT1-MMP (also known as Mmp14) plays a key role in the angiogenic process, but the mechanisms underlying its spatiotemporal regulation in the in vivo setting have not been defined. Using whole-mount immunohistochemical analysis and the lacZ gene inserted into the Mmp14 gene, we demonstrate that MT1-MMP vascular expression in vivo is confined largely to the sprouting tip of neocapillary structures where endothelial cell proliferation and collagen degradation are coordinately localized. During angiogenesis in vitro, wherein endothelial cells are stimulated to undergo neovessel formation in the presence or absence of accessory mural cells, site-specific MT1-MMP expression is shown to be controlled by crosstalk between endothelial cells and vascular smooth muscle cells (VSMC). When vessel maturation induced by VSMCs is inhibited by introducing a soluble form of the receptor tyrosine kinase Tek, MT1-MMP distribution is no longer restricted to the endothelial tip cells, but instead distributes throughout the neovessel network in vitro as well as ex vivo. Taken together, these data demonstrate that vascular maturation coordinated by endothelial cell/mural cell interactions redirects MT1-MMP expression to the neovessel tip where the protease regulates matrix remodeling at the leading edge of the developing vasculature.

Effect of a caloric restriction regimen on the angiogenic capacity of aorta and on the expression of endothelin-1 during ageing

Ageing is accompanied by impaired angiogenesis, as well as by a deficient expression of several angiogenic growth factors and the alteration of endothelial functions. Caloric restriction (CR) is the only intervention that can extend lifespan and retard age-related-decline functions in mammals by reducing the rate of ageing and the progression of the associated diseases. Herein, we have investigated the effects of ageing and of a caloric restriction regimen (mild or severe) on the angiogenic response and on the expression of endothelin-1 (ET-1) in the aorta of male 3-, 12- or 24-month-old Sprague-Dawley rats fed ad libitum (AL), fed ad libitum and fasted 1 day a week (mild CR) or fasted every other in alternate days (severe CR). Our findings, using the rat aorta ring assay, show that the angiogenic capacity of aorta decreases with ageing in the oldest rats only. Furthermore, caloric restriction counteracts the age-related changes caloric restrictions actually give raise to a similar recovery. Interestingly, the mRNA ET-1 levels as well as ET-1 expression in aorta sprouting decreases both in middle and in aged animals. Mild and severe caloric restriction regimens prevents ET-1 changes.

Sonic hedgehog carried by microparticles corrects endothelial injury through nitric oxide release

Microparticles (MPs) are small fragments generated from the plasma membrane after cell stimulation. Among the candidate proteins harbored by MPs, we recently showed that sonic hedgehog (Shh) is present in MPs generated from activated/apoptotic human T lymphocytes [Martínez et al., Blood (2006) vol. 108, 3012-3020]. We show here that Shh carried by MPs induces nitric oxide (NO) release from endothelial cells, triggers changes in the expression and phosphorylation of enzymes related to the NO pathway, and decreases production of reactive oxygen species. When PI3-kinase and ERK signaling were specifically inhibited, the effects of MPs were reversed. In vivo injection of MPs in mice was also able to improve endothelial function by increasing NO release, and it reversed endothelial dysfunction after ischemia/reperfusion. Silencing the effects of Shh with cyclopamine, a specific inhibitor of Shh, or siRNA, an inhibitor of the Shh receptor Patched, strongly reduced production of NO elicited by MPs. Taken together, we propose that the biological message carried by MPs harboring Shh may represent a new therapeutic approach against endothelial dysfunction during acute severe endothelial injury.

Integrins: novel therapeutic targets for cardiovascular diseases

Integrins are the principle mediators of molecular dialog between a cell and its extracellular matrix environment. The unique combinations of integrin subunits determine which extracellular matrix molecules are recognized by a cell. Recent studies have demonstrated that remodeling in heart and vasculature is linked to alterations in extracellular matrix and integrin expression. The roles of integrins in controlling cellular behavior have made these molecules highly attractive drug targets. New insights into mechanisms whereby the extracellular matrix takes part in the control of smooth muscle cell proliferation and cardiac growth suggest a number of putative targets for future therapies that can be applied to increase plaque stability, prevent the clinical consequences of atherosclerosis and improve outcomes after interventional procedures such as cardiac transplantation. Therapeutic candidates include antibodies, cyclic peptides, peptidomimetics and small molecules. The integrin inhibitors Integrilin and ReoPro have been approved as blood thinners in cardiovascular disease, and newer agents are undergoing testing. Although integrin function is important in the cardiovascular system, there are wide gaps in knowledge. In this review, we discuss the primary mechanisms of action and signaling of integrins in the cardiac and vascular system in normal and pathological states, as well as therapeutic strategies for targeting these molecules in the cardiovascular system.

Endothelial progenitor cells for postnatal vasculogenesis

Bone marrow-derived endothelial progenitor cells (EPCs) are present in the systemic circulation, are augmented in response to certain cytokines and/or tissue ischemia, and are home to--as well as incorporate into--sites of neovascularization. On the basis of these aspects, EPCs have attractive potential therapeutic applications for cardiovascular ischemic diseases as a novel cell-based strategy, mainly via a vasculogenesis mechanism. This review provides an update of the biology of EPCs, as well as highlighting the potential use of these cells for therapeutic regeneration.

VE-cadherin-CreERT2 transgenic mouse: a model for inducible recombination in the endothelium

To introduce temporal control in genetic experiments targeting the endothelium, we established a mouse line expressing tamoxifen-inducible Cre-recombinase (Cre-ERT2) under the regulation of the vascular endothelial cadherin promoter (VECad). Specificity and efficiency of Cre activity was documented by crossing VECad-Cre-ERT2 with the ROSA26R reporter mouse, in which a floxed-stop cassette has been placed upstream of the beta-galactosidase gene. We found that tamoxifen specifically induced widespread recombination in the endothelium of embryonic, neonatal, and adult tissues. Recombination was also documented in tumor-associated vascular beds and in postnatal angiogenesis assays. Furthermore, injection of tamoxifen in adult animals resulted in negligible excision (lower than 0.4%) in the hematopoietic lineage. The VECad-Cre-ERT2 mouse is likely to be a valuable tool to study the function of genes involved in vascular development, homeostasis, and in complex processes involving neoangiogenesis, such as tumor growth.

Development of a Humanized In Vitro Blood?Brain Barrier Model to Screen for Brain Penetration of Antiepileptic Drugs

PURPOSE

A biotechnologic breakthrough for the study of drug permeability across the blood-brain barrier (BBB) would be the use of a reproducible in vitro model that recapitulates the functional, structural, and pathologic properties of the BBB in situ. We developed a humanized dynamic in vitro BBB model (DIV-BBB) based on cocultures of human microvascular endothelial cells (HBMECs) from "normal" and drug-resistant epileptic brain tissue with human brain astrocytes (HAs) from epilepsy patients or controls.

METHODS

HBMECs and HAs were cocultured for 28 days in polypropylene capillaries. HBMECs were exposed to physiologic levels of shear stress generated by intraluminal flow. Permeability to [3H]sucrose, [14C]phenytoin, and [14C]diazepam was measured in control and drug-resistant DIV-BBB with and without pretreatment with the MDR1 inhibitor XR9576. BBB integrity was monitored by transendothelial electrical resistance measurements (TEERs). Cell growth and viability were assessed by measurement of glucose consumption and lactate production.

RESULTS

PSucrose and TEER values did not depend on the origin of the endothelium used (epileptic or normal). PPhenytoin was 10-fold less (1.54 x 10(-6) cm/s) in drug-resistant BBB models than in controls (1.74 x 10(-5) cm/s). MDR1 blockade with XR9576 was effective (3.5-fold increase) only in drug-resistant cultures. PDiazepam in control and drug-resistant DIV-BBB was not affected by XR9576 and did not depend on the epileptic or control origin of endothelia. The overall contribution of epileptic glia to pharmacoresistance was negligible.

CONCLUSIONS

These results show that, for the substances used, the humanized DIV-BBB recapitulates the physiologic permeability properties of the BBB in vivo and is also capable of mimicking a drug-resistant BBB phenotype.