Vascular wall resident progenitor cells: a review

Isolation of Vascular Wall Mesenchymal Stem Cells from the Thoracic Aorta of Adult Göttingen Minipigs: A New Protocol for the Simultaneous Endothelial Cell Collection

Two main classes of perivascular multipotent populations have been described: the microvascular pericytes and the vascular wall mesenchymal stem cells (VW-MSCs). VW-MSCs are isolated from large vessels in many species and they participate in vascular remodeling together with other cellular components such as endothelial cells. Considering that the Göttingen Minipigs are widely used in Europe as a translational model in the field of cardiovascular diseases, the aim of the present research was to isolate VW-MSCs from the adult aorta of Göttingen Minipigs while preserving and also collecting endothelial cells. The results obtained in the present research demonstrated that this new protocol allows us to obtain a pure population of VW-MSCs and endothelial cells. VW-MSCs from Göttingen Minipigs responded fully to the MSC minima international criteria, being positive to CD105, CD90, and CD44 and negative to CD45 and CD34. Moreover, VW-MSCs presented a differentiative potential towards osteogenic, chondrogenic, and adipogenic lineages. Overall, the present protocol, preserving the viability and phenotypic features of the two isolated populations, opens future possibilities of using minipig VW-MSCs and endothelial cells in in vitro vascular remodeling studies.

A histological study of vascular wall resident stem cells in venous malformations

Vascular wall resident stem cells (VW-SCs) play a key role in vascular formation and remodeling under both physiological and pathological situations. They not only serve as a reservoir to supply all types of vascular cells needed, but also regulate vascular homeostasis by paracrine effects. Venous malformations (VMs) are common congenital vascular malformations which are just characterized by the deficient quantity and abnormal function of vascular cells. However, the existence and role of VW-SCs in VMs is still unclear at present. In this study, the level and distribution of VW-SCs in 22 specimens of VMs were measured by immunochemistry, double-labeling immunofluorescence, and qPCR, followed by the Spearman rank correlation test. We found that both the protein and mRNA expression levels of CD34, vWF, VEGFR2, CD44, CD90, and CD105 were significantly downregulated in VMs compared with that in normal venules. VW-SCs were sporadically distributed or even absent within and outside the endothelium of VMs. The expression of the VW-SC-related markers was positively correlated with the density of both endothelial cells and perivascular cells. All those results and established evidence indicated that VW-SCs were more sporadically distributed with fewer amounts in VMs, which possibly contributing to the deficiency of vascular cells in VMs.

Steroid-Induced Osteonecrosis of the Femoral Head: Novel Insight Into the Roles of Bone Endothelial Cells in Pathogenesis and Treatment

Steroid-induced osteonecrosis of the femoral head (SONFH) is a disease characterized by the collapse of the femoral head. SONFH occurs due to the overuse of glucocorticoids (GCs) in patients with immune-related diseases. Among various pathogenesis proposed, the mechanism related to impaired blood vessels is gradually becoming the most convincing hypothesis. Bone endothelial cells including bone microvascular endothelial cells (BMECs) and endothelial progenitor cells (EPCs) play a crucial role in the maintenance of vascular homeostasis. Therefore, bone endothelial cells are key regulators in the occurrence and progression of SONFH. Impaired angiogenesis, abnormal apoptosis, thrombosis and fat embolism caused by the dysfunctions of bone endothelial cells are considered to be the pathogenesis of SONFH. In addition, even with high disability rates, SONFH lacks effective therapeutic approach. Icariin (ICA, a flavonoid extracted from Epimedii Herba), pravastatin, and VO-OHpic (a potent inhibitor of PTEN) are candidate reagents to prevent and treat SONFH through improving above pathological processes. However, these reagents are still in the preclinical stage and will not be widely used temporarily. In this case, bone tissue engineering represented by co-transplantation of bone endothelial cells and bone marrow mesenchymal stem cells (BMSCs) may be another feasible therapeutic strategy.

Endothelial progenitor cells as the target for cardiovascular disease prediction, personalized prevention, and treatments: progressing beyond the state-of-the-art

Stimulated by the leading mortalities of cardiovascular diseases (CVDs), various types of cardiovascular biomaterials have been widely investigated in the past few decades. Although great therapeutic effects can be achieved by bare metal stents (BMS) and drug-eluting stents (DES) within months or years, the long-term complications such as late thrombosis and restenosis have limited their further applications. It is well accepted that rapid endothelialization is a promising approach to eliminate these complications. Convincing evidence has shown that endothelial progenitor cells (EPCs) could be mobilized into the damaged vascular sites systemically and achieve endothelial repair in situ, which significantly contributes to the re-endothelialization process. Therefore, how to effectively capture EPCs via specific molecules immobilized on biomaterials is an important point to achieve rapid endothelialization. Further, in the context of predictive, preventive, personalized medicine (PPPM), the abnormal number alteration of EPCs in circulating blood and certain inflammation responses can also serve as important indicators for predicting and preventing early cardiovascular disease. In this contribution, we mainly focused on the following sections: the definition and classification of EPCs, the mechanisms of EPCs in treating CVDs, the potential diagnostic role of EPCs in predicting CVDs, as well as the main strategies for cardiovascular biomaterials to capture EPCs.

Coronary Artery Remodeling and Fibrosis With Continuous-Flow Left Ventricular Assist Device Support

BACKGROUND

Coronary artery fluid dynamics may be altered because of the nonphysiological flow seen in continuous-flow left ventricular assist devices (CF-LVADs). Our aim was to study the structure and composition of coronary vessels after CF-LVAD.

METHODS AND RESULTS

Coronary arteries were collected from patients with heart failure (HF) at the time of transplantation, of whom 15 were supported with a CF-LVAD before transplant (HF+LVAD group) and 9 were not (HF non-LVAD group). In addition, coronary samples were obtained from 5 nonfailing age-matched donors (nonfailing group). Histological analysis was performed to quantify coronary morphology, composition, vascular fibrosis, and vasa vasorum density. The age and sex mix of the 3 groups were similar, and the mean duration of LVAD support was 213 days. Compared with patients with HF and nonfailing donors, the arteries from patients with HF+LVAD had expansion of the adventitia, breakdown of the internal elastic lamina, and increased adventitial collagen deposition and density of vasa vasorum.

CONCLUSIONS

Among patients supported with CF-LVADs, the coronary arteries develop marked remodeling with increased adventitial fibrosis. The physiological consequences of these structural changes are unknown, but it is possible that arterial contractility may be impaired, thus limiting coronary flow reserve and promoting myocardial ischemia. This may contribute to CF-LVAD complications, such as ventricular arrhythmias and right ventricular failure. As more patients receive CF-LVADs and new pump technology attempts to modulate flow profiles and pulsatility, further research is needed to understand the mechanisms and long-term sequela of these changes in coronary arteries and other vascular beds.

Vascular stem/progenitor cells: functions and signaling pathways

Vascular stem/progenitor cells (VSCs) are an important source of all types of vascular cells needed to build, maintain, repair, and remodel blood vessels. VSCs, therefore, play critical roles in the development, normal physiology, and pathophysiology of numerous diseases. There are four major types of VSCs, including endothelial progenitor cells (EPCs), smooth muscle progenitor cells (SMPCs), pericytes, and mesenchymal stem cells (MSCs). VSCs can be found in bone marrow, circulating blood, vessel walls, and other extravascular tissues. During the past two decades, considerable progress has been achieved in the understanding of the derivation, surface markers, and differentiation of VSCs. Yet, the mechanisms regulating their functions and maintenance under normal and pathological conditions, such as in eye diseases, remain to be further elucidated. Owing to the essential roles of blood vessels in human tissues and organs, understanding the functional properties and the underlying molecular basis of VSCs is of critical importance for both basic and translational research.

Mechanisms of Arterial Calcification: The Role of Matrix Vesicles

Vascular calcification is related to vascular diseases, for example, atherosclerosis, and its comorbidities, such as diabetes and chronic kidney disease. In each condition, a distinctive histological pattern can be recognised that may influence technical choices, possible intra-operative complications, and procedure outcomes, no matter if the intervention is performed by open or endovascular means. This review considers the classification and initiating mechanisms of vascular calcification. Dystrophic and metastatic calcifications, Monckeberg's calcification, and genetic forms are firstly outlined, followed by their alleged initiation mechanisms; these include (a) ineffective macrophage efferocytosis; (b) ectopic osteogenesis driven by modified resident or circulating osteoprogenitors. As in physiological bio-mineralisation, active calcification starts with the deposition of cell derived matrix vesicles into the extracellular matrix. To substantiate this belief, an in depth ultra-structural documentation of hydroxyapatite crystal deposition on such vesicles is provided in an ex-vivo human vascular cell model. Revealing the vesicle composition and phenotype in normal and pathological vascular conditions will be essential for the development of new therapeutic strategies, in order to prevent and treat vascular calcification.

Cell Based Therapeutic Approach in Vascular Surgery: Application and Review

Multipotent stem cells - such as mesenchymal stem/stromal cells and stem cells derived from different sources like vascular wall are intensely studied to try to rapidly translate their discovered features from bench to bedside. Vascular wall resident stem cells recruitment, differentiation, survival, proliferation, growth factor production, and signaling pathways transduced were analyzed. We studied biological properties of vascular resident stem cells and explored the relationship from several factors as Matrix Metalloproteinases (MMPs) and regulations of biological, translational and clinical features of these cells. In this review we described a translational and clinical approach to Adult Vascular Wall Resident Multipotent Vascular Stem Cells (VW-SCs) and reported their involvement in alternative clinical approach as cells based therapy in vascular disease like arterial aneurysms or peripheral arterial obstructive disease.

Age-related Impairment of Vascular Structure and Functions

Among age-related diseases, cardiovascular and cerebrovascular diseases are major causes of death. Vascular dysfunction is a key characteristic of these diseases wherein age is an independent and essential risk factor. The present work will review morphological alterations of aging vessels in-depth, which includes the discussion of age-related microvessel loss and changes to vasculature involving the capillary basement membrane, intima, media, and adventitia as well as the accompanying vascular dysfunctions arising from these alterations.

Immaturity for gestational age of microvasculature and placental barrier in term placentas with high weight

OBJECTIVE

Villous immaturity for gestational age is a multifactorial developmental deviation associated with unexpected placental insufficiency, fetal hypoxia and term fetal death. In our previous work we have shown that immature CD15+/CD31+/CD34+ endothelial cells were an important indicator of placental villous immaturity and chronic insufficiency. The aim of this study was to perform a comparative analysis of CD15-marked immaturity in the vessel walls between normal and pathological term placentas of clinically and structurally heterogenous groups with normal, low and high weight.

STUDY DESIGN

165 clinically normal and pathological placentas of gestational age 39-42 with normal weight (25-75 percentile), low weight (<10 percentile) and high weight (>90 percentile) were structurally and immunohistochemically analyzed. Excluded were placentas with a severe form of placental insufficiency associated with intrauterine fetal death, low APGAR-score, genetic and chromosomal diseases or placental inflammations. The distribution patterns of CD15, CD31 and CD34 were assessed separately in the macrovasculature, microvasculature and placental barrier (PB) - associated capillaries.

RESULTS

All placental groups with normal weight, low weight and high weight include normal, accelerated villous maturation or villous immaturity independent of their weight. However, a significant increase of immature CD15+/CD31+/CD34+ endothelial cells was detected in microvasculature and PB -associated capillaries in high weight-placentas (63.5%/52.2%), compared to those of normal weight (13.8%/8.2%) and low weight (16.1%/17.8%). The distribution of macrovascular immature CD15+/CD31+/CD34+ endothelial cells did not show such marked differences.

CONCLUSION

We have identified the immaturity of microvasculature and PB -associated capillaries with a pathological persistency of immature CD15+/CD31+/CD34+ endothelial cells and a reduction of terminally differentiated CD15-/CD31+/CD34+ endothelial cells in a structurally and clinically heterogeneous group of high weight-placentas. We assume that immaturity of placental vessels are part of prenatal adaptational processes that can be recruited in different emergency situations and may provide potential targets of therapeutic correction of placental growth and chronic insufficiency. We therefore recommend the use of CD15-based immunophenotyping as a method to identify latent unfavorable conditions of fetal development in the intrauterine life and individual risk of disease in the postnatal period.

Integrin α6β1 Expressed in ESCs Instructs the Differentiation to Endothelial Cells

Adhesion of embryonic stem cells (ESCs) to the extracellular matrix may influence differentiation potential and cell fate decisions. Here, we investigated the inductive role of binding of integrin α6β1 expressed in mouse (m)ESCs to laminin-1 (LN1) in mediating the differentiation of ESCs to endothelial cells (ECs). We observed that α6β1 binding to LN1 was required for differentiation to ECs. α6β1 functioned by recruiting the adaptor tetraspanin protein CD151, which activated FAK and Akt signaling and mediated the EC lineage-specifying transcription factor Er71. In contrast, association of the ESC-expressed α3β1, another highly expressed LN1 binding integrin, with CD151, prevented α6β1-mediated differentiation. CD151 thus functioned as a bifurcation router to direct ESCs toward ECs when α6β1 associated with CD151, or prevented transition to ECs when α3β1 associated with CD151. These observations were recapitulated in mice in which α6 integrin or CD151 knockdown reduced the expression of Er71-regulated angiogenesis genes and development of blood vessels. Thus, interaction of α6β1 in ESCs with LN1 activates α6β1/CD151 signaling which programs ESCs toward the EC lineage fate.

In vitro differentiation of porcine aortic vascular precursor cells to endothelial and vascular smooth muscle cells

Recent findings suggest that progenitor and multipotent mesenchymal stromal cells (MSCs) are associated with vascular niches. Cells displaying mesenchymal properties and differentiating to whole components of a functional blood vessel, including endothelial and smooth muscle cells, can be defined as vascular stem cells (VSCs). Recently, we isolated a population of porcine aortic vascular precursor cells (pAVPCs), which have MSC- and pericyte-like properties. The aim of the present work was to investigate whether pAVPCs possess VSC-like properties and assess their differentiation potential toward endothelial and smooth muscle lineages. pAVPCs, maintained in a specific pericyte growth medium, were cultured in high-glucose DMEM + 10% FBS (long-term medium, LTM) or in human endothelial serum-free medium + 5% FBS and 50 ng/ml of hVEGF (endothelial differentiation medium, EDM). After 21 days of culture in LTM, pAVPCs showed an elongated fibroblast-like morphology, and they seem to organize in cord-like structures. qPCR analysis of smooth muscle markers [α-smooth muscle actin (α-SMA), calponin, and smooth muscle myosin (SMM) heavy chain] showed a significant increment of the transcripts, and immunofluorescence analysis confirmed the presence of α-SMA and SMM proteins. After 21 days of culture in EDM, pAVPCs displayed an endothelial cell-like morphology and revealed the upregulation of the expression of endothelial markers (CD31, vascular endothelial-cadherin, von Willebrand factor, and endothelial nitric oxide synthase) showing the CD31-typical pattern. In conclusion, pAVPCs could be defined as a VSC-like population considering that, if they are maintained in a specific pericyte medium, they express MSC markers, and they have, in addition to the classical mesenchymal trilineage differentiation potential, the capacity to differentiate in vitro toward the smooth muscle and the endothelial cell phenotypes.

Adult vascular wall resident multipotent vascular stem cells, matrix metalloproteinases, and arterial aneurysms

Evidences have shown the presence of multipotent stem cells (SCs) at sites of arterial aneurysms: they can differentiate into smooth muscle cells (SMCs) and are activated after residing in a quiescent state in the vascular wall. Recent studies have implicated the role of matrix metalloproteinases in the pathogenesis of arterial aneurysms: in fact the increased synthesis of MMPs by arterial SMCs is thought to be a pivotal mechanism in aneurysm formation. The factors and signaling pathways involved in regulating wall resident SC recruitment, survival, proliferation, growth factor production, and differentiation may be also related to selective expression of different MMPs. This review explores the relationship between adult vascular wall resident multipotent vascular SCs, MMPs, and arterial aneurysms.

BRG1 overexpression in smooth muscle cells promotes the development of thoracic aortic dissection

Background

Here we investigated Brahma-related gene 1 (BRG1) expression in aortic smooth muscle cells (SMCs) and its role in the regulation of the pathological changes in aortic SMCs of thoracic arotic dissection (TAD).

Methods

BRG1, matrix metalloproteinase 2 (MMP2), and MMP9 mRNA and protein expression in human aortic specimens were examined by qPCR and western blot, respectively. The percentage of apoptotic and contractile SMCs in aortic specimens were determined by TUNEL assay and α-SMA immunohistochemical staining, respectively. The role of BRG1 in MMP2 and MMP9 expression, cell apoptosis, and phenotype transition in aortic SMCs were investigated using a human aortic SMC line via adenovirus mediated gene transfer. MMPs mRNA and protein levels were analyzed by qPCR and western blot, respectively. The percentage of apoptotic and contractile cells were determined through flow cytometry analysis.

Results

The expression level of BRG1 in the aortic walls (adventitia-removed) was significantly higher in the TAD than the normal group. BRG1 expression was positively correlated to expression of MMP2 and MMP9 and SMC apoptosis, but was negatively correlated to the percentage of contractile aortic SMCs in TAD specimens. In human aortic SMC line, BRG1 transfection led to significant upregulation of MMP2 and MMP9 expression and a concomitant increase in SMC apoptosis as well as a decrease in the percentage of contractile phenotype of cells.

Conclusions

BRG1 is significantly upregulated in the aortic SMCs of TAD, and its overexpression might promote the development of TAD by increasing MMP2 and MMP9 expression, inducing SMC apoptosis and the transition from contractile to synthetic phenotype.

Cellular players in skeletal muscle regeneration

Skeletal muscle, a tissue endowed with remarkable endogenous regeneration potential, is still under focused experimental investigation mainly due to treatment potential for muscle trauma and muscular dystrophies. Resident satellite cells with stem cell features were enthusiastically described quite a long time ago, but activation of these cells is not yet controlled by any medical interventions. However, after thorough reports of their existence, survival, activation, and differentiation there are still many questions to be answered regarding the intimate mechanism of tissue regeneration. This review delivers an up-to-date inventory of the main known key players in skeletal muscle repair, revealed by various models of tissue injuries in mechanical trauma, toxic lesions, and muscular dystrophy. A better understanding of the spatial and temporal relationships between various cell populations, with different physical or paracrine interactions and phenotype changes induced by local or systemic signalling, might lead to a more efficient approach for future therapies.

Delivery of Polymeric Nanoparticles to Target Vascular Diseases

Current advances in nanotechnology have paved the way for the early detection, prevention and treatment of various diseases such as vascular disorders and cancer. These advances have provided novel approaches or modalities of incorporating or adsorbing therapeutic, biosensor and targeting agents into/on nanoparticles. With significant progress, nanomedicine for vascular therapy has shown significant advantages over traditional medicine because of its ability to selectively target the disease site and reduce adverse side effects. Targeted delivery of nanoparticles to vascular endothelial cells or the vascular wall provides an effective and more efficient way for early detection and/or treatment of vascular diseases such as atherosclerosis, thrombosis and Cerebrovascular Amyloid Angiopathy (CAA). Clinical applications of biocompatible and biodegradable polymers in areas such as vascular graft, implantable drug delivery, stent devices and tissue engineering scaffolds have advanced the candidature of polymers as potential nano-carriers for vascular-targeted delivery of diagnostic agents and drugs. This review focuses on the basic aspects of the vasculature and its associated diseases and relates them to polymeric nanoparticle-based strategies for targeting therapeutic agents to diseased vascular site.

Cells derived from porcine aorta tunica media show mesenchymal stromal-like cell properties in in vitro culture

Several studies have already described the presence of specialized niches of precursor cells in vasculature wall, and it has been shown that these populations share several features with mesenchymal stromal cells (MSCs). Considering the relevance of MSCs in the cardiovascular physiopathology and regenerative medicine, and the usefulness of the pig animal model in this field, we reported a new method for MSC-like cell isolation from pig aorta. Filling the vessel with a collagenase solution for 40 min, all endothelial cells were detached and discarded and then collagenase treatment was repeated for 4 h to digest approximately one-third of the tunica media. The ability of our method to select a population of MSC-like cells from tunica media could be ascribed in part to the elimination of contaminant cells from the intimal layer and in part to the overnight culture in the high antibiotic/antimycotic condition and to the starvation step. Aortic-derived cells show an elongated, spindle shape, fibroblast-like morphology, as reported for MSCs, stain positively for CD44, CD56, CD90, and CD105; stain negatively for CD34 and CD45; and express CD73 mRNA. Moreover, these cells show the classical mesenchymal trilineage differentiation potential. Under our in vitro culture conditions, aortic-derived cells share some phenotypical features with pericytes and are able to take part in the formation of network-like structures if cocultured with human umbilical vein endothelial cells. In conclusion, our work reports a simple and highly suitable method for obtaining large numbers of precursor MSC-like cells derived from the porcine aortic wall.

Blood flow and stem cells in vascular disease

It is well known that the altered blood flow is related to vascular diseases, including atherosclerosis, restenosis, and arteriosclerosis, which preferentially located at areas with the disturbed blood flow, suggesting that altered biomechanical stress may exert their effect on the vascular disease. Recent evidence indicated the presence of abundant stem/progenitor cells in the vessel wall, in which laminar shear stress can stimulate these cells to differentiate towards endothelial lineage, while cyclic strain results in smooth muscle differentiation. In line with this, it was evidenced that altered biomechanical stress in stented vessels may lead to 'wrong' direction of vascular stem cell differentiation resulting in restenosis. However, the underlying mechanisms are not well understood. In this article, we will give an overview of the effect of the local flow pattern on stem/progenitor cell differentiation and the possible mechanism on how the blood flow influences stem cell behaviours in the development of vascular diseases.

Phenotypic characterization and in vivo localization of human adipose-derived mesenchymal stem cells

Human adipose-derived mesenchymal stem cells (hADMSCs) are a potential cell source for autologous cell therapy due to their regenerative ability. However, detailed cytological or phenotypic characteristics of these cells are still unclear. Therefore, we determined and compared cell size, morphology, ultrastructure, and immunohistochemical (IHC) expression profiles of isolated hADMSCs and cells located in human adipose tissues. We also characterized the localization of these cells in vivo. Light microscopy examination at low power revealed that hADMSCs acquired a spindle-shaped morphology after four passages. Additionally, high power views showed that these cells had various sizes, nuclear contours, and cytoplasmic textures. To further evaluate cell morphology, transmission electron microscopy was performed. hADMSCs typically had ultrastructural characteristics similar to those of primitive mesenchymal cells including a relatively high nuclear/cytosol ratio, prominent nucleoli, immature cytoplasmic organelles, and numerous filipodia. Some cells contained various numbers of lamellar bodies and lipid droplets. IHC staining demonstrated that PDGFR and CD10 were constitutively expressed in most hADMSCs regardless of passage number but expression levels of α-SMA, CD68, Oct4 and c-kit varied. IHC staining of adipose tissue showed that cells with immunophenotypic characteristics identical to those of hADMSCs were located mainly in the perivascular adventitia not in smooth muscle area. In summary, hADMSCs were found to represent a heterogeneous cell population with primitive mesenchymal cells that were mainly found in the perivascular adventitia. Furthermore, the cell surface markers would be CD10/PDGFR. To obtain defined cell populations for therapeutic purposes, further studies will be required to establish more specific isolation methods.

Autologous transplantation of endothelial progenitor cells to prevent multiple organ dysfunction syndromes in pig

BACKGROUND

It was observed that the number and function of endothelial progenitor cells (EPCs) decreased sharply in the progression of multiple organ dysfunction syndrome (MODS), and it may be the main pathogenesis for MODS. We aim to perform autologous transplantation of EPCs on animal models of MODS to investigate whether EPCs might be used to prevent MODS caused by severe sepsis.

METHODS

A total of 60 pigs were randomly divided into three groups: subjected to hemorrhagic shock + resuscitation + endotoxemia only (MODS group); performed autologous transplantation of EPCs after hemorrhagic shock + resuscitation + endotoxemia (transplantation group); and control group. Mononuclear cells of animals of the transplantation group were isolated by density-gradient centrifugation for ex vivo expansion, and the six-passage EPCs labeled with 5-carboxyfluorescein diacetate succinimidyl ester were autologously transplanted at a density of 1 × 10(7) cells/kg body weight at the 24th hour after endotoxemia. The function of important organs was monitored continuously to assess the effects of autologous transplantation of EPCs on MODS.

RESULTS

All animals of the MODS group developed MODS (100%), and 17 (85%) of 20 animals died because of MODS; the incidence of MODS and mortality rate in the transplantation group were 45% (9 of 20 pigs; p < 0.01) and 35% (7 of 20 pigs; p < 0.01). In transplantation group, the incidence of pulmonary dysfunction, cardiac dysfunction, hepatosis, and renal dysfunction were 40%, 10%, 5%, and 15%, respectively. The capillary densities of important organs, including the heart, liver, kidney, intestine, and lung, after autologous transplantation of EPCs were significantly higher than those in the MODS group (p < 0.01).

CONCLUSION

Autologous transplantation of EPCs could migrate to injured organs and induce angiogenesis to restore blood flow that could improve the function of important organs. It could prevent the incidence of MODS and reduce mortality rate caused by trauma and severe sepsis. Autologous transplantation of EPCs would be a novel, cell-based, vascular endothelium-targeted therapeutic strategy for MODS.

Defining vascular stem cells

Mesenchymal stem cells (MSCs) exist in most adult tissues and have been located near or within blood vessels. Although "perivascular" has been commonly used to describe such locations, increasing evidence points at the vessel wall as the exact location. Thus, "vascular stem cells (VSCs)" is recommended as a more accurate term for MSCs. Furthermore, 2 cell populations, namely pericytes and adventitial progenitor cells (APCs), are the likely VSCs. The pericyte evidence relies on the so-called pericyte-specific markers, but none of these markers is pericyte specific. In addition, pericytes appear to be too functionally diverse and sophisticated to have a large differentiation capacity. On the other hand, APCs are more naïve functionally and, therefore, more akin to being VSCs. In vitro, these cells spontaneously differentiate into pericytes, and can be induced to differentiate into vascular cells (endothelial and smooth muscle cells) and mesenchymal cells (e.g., bone, cartilage, and fat). In vivo, indirect evidence also points to their ability to differentiate into mesenchymal cells of their native tissue (e.g., fat). Moreover, they possess a large paracrine capacity and, therefore, can help maintain tissue homeostasis by encouraging the replication and differentiation of mesenchymal cells locally. These proposed in vivo functions are areas of interest for future research on VSCs.

Adventitial pericyte progenitor/mesenchymal stem cells participate in the restenotic response to arterial injury

Restenosis is a major complication of coronary angioplasty, at least partly due to the fact that the origin and identity of contributing cell types are not well understood. In this study, we have investigated whether pericyte-like cells or mesenchymal stem cells (MSCs) from the adventitia contribute to restenosis. We demonstrate that while cells expressing the pericyte markers NG2, platelet-derived growth factor receptor β, and CD146 are rare in the adventitia of uninjured mouse femoral arteries, following injury their numbers strongly increase. Some of these adventitial pericyte-like cells acquire a more MSC-like phenotype (CD90+ and CD29+ are up-regulated) and also appear in the restenotic neointima. Via bone marrow transplantation and ex vivo artery culture approaches, we demonstrate that the pericyte-like MSCs of the injured femoral artery are not derived from the bone marrow, but originate in the adventitia itself mainly via the proliferation of resident pericyte-like cells. In summary, we have identified a population of resident adventitial pericyte-like cells or MSCs that contribute to restenosis following arterial injury. These cells are different from myofibroblasts, smooth muscle cells, and other progenitor populations that have been shown to participate in the restenotic process.

The emerging issue of human resident arterial progenitors: the contribution of organ culture

Human femoral arteries were cultured up to 56 days. Samples were processed for light, immunohistochemical, and transmission electron microscopy. Arteries became rapidly depopulated; at day 42, an endothelial lining (CD31(+), Weibel-Palade bodies) developed on the intima; endothelium was in continuity with mesenchymal stromal cells (CD44(+), CD90(low), CD105(low)) placed on adventitia. The media-adventitia area showed heterogeneous cell populations. In long-term organ culture, femoral artery develops a continuous cell coverage that differentiates to endothelium on the intima exclusively. This suggests that distinct topographical factors, such as resident progenitors and/or matrix signals, are able to regulate vascular homeostasis in adult life.

Use of electron microscopy to classify canine perivascular wall tumors

The histologic classification of canine perivascular wall tumors (PWTs) is controversial. Many PWTs are still classified as hemangiopericytomas (HEPs), and the distinction from peripheral nerve sheath tumors (PNSTs) is still under debate. A recent histologic classification of canine soft tissue sarcomas included most histologic types of PWT but omitted those that were termed undifferentiated. Twelve cases of undifferentiated canine PWTs were evaluated by transmission electron microscopy. The ultrastructural findings supported a perivascular wall origin for all cases with 4 categories of differentiation: myopericytic (n = 4), myofibroblastic (n = 1), fibroblastic (n = 2), and undifferentiated (n = 5). A PNST was considered unlikely in each case based on immunohistochemical expression of desmin and/or the lack of typical ultrastructural features, such as basal lamina. Electron microscopy was pivotal for the subclassification of canine PWTs, and the results support the hypothesis that canine PWTs represent a continuum paralleling the phenotypic plasticity of vascular mural cells. The hypothesis that a subgroup of PWTs could arise from a pluripotent mesenchymal perivascular wall cell was also considered and may explain the diverse differentiation of canine PWTs.

Identification and characterization of novel perivascular adventitial cells in the whole mount mesenteric branch artery using immunofluorescent staining and scanning confocal microscopy imaging

A novel perivascular adventitial cell termed, adventitial neuronal somata (ANNIES) expressing the neural cell adhesion molecule (NCAM) and the vasodilator neuropeptide, calcitonin gene-related peptide (CGRP), exists in the adult rat mesenteric branch artery (MBA) in situ. In addition, we have previously shown that ANNIES coexpress CGRP and NCAM. We now show that ANNIES express the neurite growth marker, growth associated protein-43(Gap-43), palladin, and the calcium sensing receptor (CaSR), that senses changes in extracellular Ca(2+) and participates in vasodilator mechanisms. Thus, a previously characterized vasodilator, calcium sensing autocrine/paracrine system, exists in the perivascular adventitia associated with neural-vascular interface. Images of the whole mount MBA segments were analyzed under scanning confocal microscopy. Confocal analysis showed that the Gap-43, CaSR, and palladin were present in ANNIES about 37 ± 4%, 94 ± 6%, and 80 ± 10% respectively, comparable to CGRP (100%). Immunoblots from MBA confirmed the presence of Gap-43 (48 kD), NCAM (120 and 140 kD), and palladin (90–92 and 140 kD). In summary, CGRP, and NCAM-containing neural cells in the perivascular adventitia also express palladin and CaSR, and coexpress Gap-43 which may participate in response to stress/injury and vasodilator mechanisms as part of a perivascular sensory neural network.

Postnatal changes in the expression pattern of the imprinted signalling protein XLαs underlie the changing phenotype of deficient mice

The alternatively spliced trimeric G-protein subunit XLαs, which is involved in cAMP signalling, is encoded by the Gnasxl transcript of the imprinted Gnas locus. XLαs deficient mice show neonatal feeding problems, leanness, inertia and a high mortality rate. Mutants that survive to weaning age develop into healthy and fertile adults, which remain lean despite elevated food intake. The adult metabolic phenotype can be attributed to increased energy expenditure, which appears to be caused by elevated sympathetic nervous system activity. To better understand the changing phenotype of Gnasxl deficient mice, we compared XLαs expression in neonatal versus adult tissues, analysed its co-localisation with neural markers and characterised changes in the nutrient-sensing mTOR1-S6K pathway in the hypothalamus. Using a newly generated conditional Gnasxl lacZ gene trap line and immunohistochemistry we identified various types of muscle, including smooth muscle cells of blood vessels, as the major peripheral sites of expression in neonates. Expression in all muscle tissues was silenced in adults. While Gnasxl expression in the central nervous system was also developmentally silenced in some midbrain nuclei, it was upregulated in the preoptic area, the medial amygdala, several hypothalamic nuclei (e.g. arcuate, dorsomedial, lateral and paraventricular nuclei) and the nucleus of the solitary tract. Furthermore, expression was detected in the ventral medulla as well as in motoneurons and a subset of sympathetic preganglionic neurons of the spinal cord. In the arcuate nucleus of Gnasxl-deficient mice we found reduced activity of the nutrient sensing mTOR1-S6K signalling pathway, which concurs with their metabolic status. The expression in these brain regions and the hypermetabolic phenotype of adult Gnasxl-deficient mice imply an inhibitory function of XLαs in energy expenditure and sympathetic outflow. By contrast, the neonatal phenotype of mutant mice appears to be due to a transient role of XLαs in muscle tissues.

Chronic hyperhomocysteinemia causes vascular remodelling by instigating vein phenotype in artery

In the present study we tested the hypothesis whether hyperhomocysteinemia, an elevated homocysteine level, induces venous phenotype in artery. To test our hypothesis, we employed wild type (WT) and cystathionine β-synthase heterozygous (+/-) (CBS+/-) mice treatment with or without folic acid (FA). Aortic blood flow and velocity were significantly lower in CBS+/-mice compared to WT. Aortic lumen diameter was significantly decreased in CBS+/-mice, whereas FA treatment normalized it. Medial thickness and collagen were significantly increased in CBS+/-aorta, whereas elastin/collagen ratio was significantly decreased. Superoxide and gelatinase activity was significantly high in CBS+/-aorta vs WT. Western blot showed significant increase in MMP-2, -9,-12, TIMP-2 and decrease in TIMP-4 in aorta. RT-PCR revealed significant increase of vena cava marker EphB4, MMP-13 and TIMP-3 in aorta. We summarize that chronic HHcy causes vascular remodelling that transduces changes in vascular wall in a way that artery expresses vein phenotype.

Human embryonic stem cell-derived vascular smooth muscle cells in therapeutic neovascularisation

Ischemic diseases remain one of the major causes of morbidity and mortality throughout the world. In recent clinical trials on cell-based therapies, the use of adult stem and progenitor cells only elicited marginal benefits. Therapeutic neovascularisation is the Holy Grail for ischemic tissue recovery. There is compelling evidence from animal transplantation studies that the inclusion of mural cells in addition to endothelial cells (ECs) can enhance the formation of functional blood vessels. Vascular smooth muscle cells (SMCs) and pericytes are essential for the stabilisation of nascent immature endothelial tubes. Despite the intense interest in the utility of human embryonic stem cells (ESCs) for vascular regenerative medicine, ESC-derived vascular SMCs have received much less attention than ECs. This review begins with developmental insights into a range of smooth muscle progenitors from studies on embryos and ESC differentiation systems. We then summarise the methods of derivation of smooth muscle progenitors and cells from human ESCs. The primary emphasis is on the inherent heterogeneity of smooth muscle progenitors and cells and the limitations of current in vitro characterisation. Essential transplantation issues such as the type and source of therapeutic cells, mode of cell delivery, measures to enhance cell viability, putative mechanisms of benefit and long-term tracking of cell fate are also discussed. Finally, we highlight the challenges of clinical compatibility and scaling up for medical use in order to eventually realise the goal of human ESC-based vascular regenerative medicine.

Identification of a coronary stem cell in the human heart

Human ischemic cardiomyopathy is characterized by de novo cardiomyogenesis, which is limited to the surviving portion of the ventricle, and by organ hypertrophy that develops as a chronic response to ischemic injury. Although myocyte hypertrophy and myocyte regeneration restore the original myocardial mass, the coronary vasculature remains defective and the extent and regulation of myocardial perfusion are severely impaired. Recently, vascular stem cells (VSCs) have been identified in the coronary circulation. VSCs express c-kit and the vascular endothelial growth factor receptor-2, KDR. These cells are self-renewing, clonogenic, and multipotent in vitro and in vivo. In animal models of critical coronary artery stenosis, VSCs form large conductive coronary arteries and their distal branches. This degree of vasculogenesis replaces partly the function of the occluded coronary artery improving myocardial perfusion and positively interfering with the development of the post-infarction myopathy. Cell therapy directed to the restoration of the integrity of the coronary circulation, the replacement of atherosclerotic coronary vessels, or both, would change dramatically the goal of cell therapy for the ischemic heart: the prevention of myocardial injury would become the end-point of cell therapy rather than the partial recovery of established damage.

Multilineage stem cells in the adult: a perivascular legacy?

Mesenchymal stem cells proliferate extensively in cultures of unselected, total cell isolates from multiple fetal and adult organs. Perivascular cells, principally pericytes surrounding capillaries and microvessels, but also adventitial cells located around larger arteries and veins, have been recently identified as possible originators of mesenchymal stem cells, first by phenotypic analogies and eventually following stringent cell sorting. While it is clear that purified perivascular cells exhibit multiple mesodermal developmental potentials and become indistinguishable from conventionally derived mesenchymal stem cells after in vitro culture, the possible roles played by these blood vessel-bound cells in organogenesis and adult tissue repair remain elusive. Unsolved questions regarding the identity of mesenchymal stem cells have not compromised the consideration of these cells as outstanding candidates for cell therapies. Better knowledge of the lineage affiliation, tissue distribution and molecular identity of mesenchymal stem cells will contribute to the development of more efficient, safer therapeutic cells.

Adult human adipose tissue contains several types of multipotent cells

Multipotent mesenchymal stromal cells (MSCs) are a type of adult stem cells that can be easily isolated from various tissues and expanded in vitro. Many reports on their pluripotency and possible clinical applications have raised hopes and interest in MSCs. In an attempt to unify the terminology and the criteria to label a cell as MSC, in 2006 the International Society for Cellular Therapy (ISCT) proposed a standard set of rules to define the identity of these cells. However, MSCs are still extracted from different tissues, by diverse isolation protocols, are cultured and expanded in different media and conditions. All these variables may have profound effects on the selection of cell types and the composition of heterogeneous subpopulations, on the selective expansion of specific cell populations with totally different potentials and ergo, on the long-term fate of the cells upon in vitro culture. Therefore, specific molecular and cellular markers that identify MSCs subsets as well as standardization of expansion protocols for these cells are urgently needed. Here, we briefly discuss new useful markers and recent data supporting the rapidly emerging concept that many different types of progenitor cells are found in close association with blood vessels. This knowledge may promote the necessary technical improvements required to reduce variability and promote higher efficacy and safety when isolating and expanding these cells for therapeutic use. In the light of the discussed data, particularly the identification of new markers, and advances in the understanding of fundamental MSC biology, we also suggest a revision of the 2006 ISCT criteria.

Engineering blood vessels using stem cells: innovative approaches to treat vascular disorders

Vascular disease is the leading cause of mortality in the USA, providing the impetus for new treatments and technologies. Current therapies rely on the implantation of stents or grafts to treat injured blood vessels. However, these therapies may be immunogenic or may incompletely recover the functional integrity of the vasculature. In light of these shortcomings, cell-based therapies provide new treatment options to heal damaged areas with more suitable substitutes. Current clinical trials employing stem cell-based therapies involve the transfusion of harvested endothelial progenitor cells. While the results from these trials have been encouraging, utilizing tissue-engineered approaches could yield technologically advanced solutions. This article discusses engineered stem cell-based therapies from three angles: the differentiation of adult stem cells, such as mesenchymal stem cells and endothelial progenitor cells, into vascular lineages; investigation of human embryonic stem cells and induced pluripotent stem cells as inexhaustible sources of vascular cells; and tissue-engineering approaches, which incorporate these vascular progenitor cells into biomimetic scaffolds to guide regeneration. The optimal solution to vascular disease lies at the interface of these technologies--embedding differentiated cells into engineered scaffolds to impart precise control over vascular regeneration.

High-resolution mass spectrometric analysis of the secretome from mouse lung endothelial progenitor cells

Recently, we isolated and characterized resident endothelial progenitor cells from the lungs of adult mice. These cells have a high proliferation potential, are not transformed and can differentiate into blood- and lymph-vascular endothelial cells under in vitro and in vivo conditions. Here we studied the secretome of these cells by nanoflow liquid chromatographic mass spectrometry (LC-MS). For analysis, 3-day conditioned serum-free media were used. We found 133 proteins belonging to the categories of membrane-bound or secreted proteins. Thereby, several of the membrane-bound proteins also existed as released variants. Thirty-five proteins from this group are well known as endothelial cell- or angiogenesis-related proteins. The MS analysis of the secretome was supplemented and confirmed by fluorescence activated cell sorting analyses, ELISA measurements and immunocytological studies of selected proteins. The secretome data presented in this study provides a platform for the in-depth analysis of endothelial progenitor cells and characterizes potential cellular markers and signaling components in hem- and lymphangiogenesis.

Multidistrict human mesenchymal vascular cells: pluripotency and stemness characteristics

BACKGROUND AIMS

The presence of ectopic tissues in the pathologic artery wall raises the issue of whether multipotent stem cells may reside in the vasculature itself. Recently mesenchymal stromal cells (MSC) have been isolated from different human vascular segments (VW MSC), belying the previous view that the vessel wall is a relatively quiescent tissue.

METHODS

Resident multipotent cells were recovered from fresh arterial segments (aortic arches, thoracic and femoral arteries) collected in a tissue-banking facility and used to establish an in situ and in vitro study of the stemness features and multipotency of these multidistrict MSC populations.

RESULTS

Notch-1+, Stro-1+, Sca-1+ and Oct-4+ cells were distributed along an arterial wall vasculogenic niche. Multidistrict VW MSC homogeneously expressed markers of stemness (Stro-1, Notch-1 and Oct-4) and MSC lineages (CD44, CD90, CD105, CD73, CD29 and CD166) whilst they were negative for hematopoietic and endothelial markers (CD34, CD45, CD31 and vWF). Each VW MSC population had characteristics of stem cells, i.e. a high efflux capability for Hoechst 33342 dye and the ability to form spheroids when grown in suspension and generate colonies when seeded at low density. Again, VW MSC cultured in induction media exhibited adipogenic, chondrogenic and leiomyogenic potential but less propensity to osteogenic differentiation, as documented by histochemical, immunohistochemical, molecular and electron microscopy analysis.

CONCLUSIONS

Overall, these findings may enlighten the physiopathologic mechanisms of vascular wall diseases as well as having potential implications for cellular, genetic and tissue engineering approaches to treating vascular pathologies when these are unresponsive to medical and surgical therapies.

Emerging use of stem cells in regenerative medicine

Stem cells represent a unique opportunity for regenerative medicine to cure a broad number of diseases for which current treatment only alleviates symptoms or retards further disease progression. However, the number of stem cells available has speedily increased these past 10 years and their diversity presents new challenges to clinicians and basic scientists who intend to use them in clinics or to study their unique properties. In addition, the recent possibility to derive pluripotent stem cells from somatic cells using epigenetic reprogramming has further increased the clinical interest of stem cells since induced pluripotent stem cells could render personalized cell-based therapy possible. The present review will attempt to summarize the advantages and challenges of each type of stem cell for current and future clinical applications using specific examples.

Endothelial progenitor cells--an evolving story

The first description of endothelial progenitor cells (EPC) in 1997 led rapidly to substantial changes in our understanding of angiogenesis, and within 5 years to the first clinical studies in humans using bone marrow derived EPC to enhance coronary neovascularisation and cardiac function after myocardial ischemia. However, to improve the success of this therapy a clearer understanding of the biology of EPC is needed. This article summarises recent data indicating that most EPC are not, in fact, endothelial progenitors but can be better described as angiogenic monocytes, and explores the implications this has for their future therapeutic use.

Autologous transplantation of arterial cells improves cardiac function in a rabbit model of infarcted myocardium

Cellular cardiomyoplasty is a promising approach for the treatment of severe heart failure. However, the question which cell line is the best to use is still a matter of debate. In this study, we aimed to evaluate the efficacy of arterial media-intima cell suspension (AMICS) transplantation in rabbit myocardial infarct model. The study was divided into 2 groups: group A (the cell-treated group, n = 9) and group B (the medium injection group, n = 8). Group A was further divided into 2 subgroups as branch-1 (treated with unlabeled cells) and branch-2 (treated with iron-labeled cells). The experimental myocardial infarction (MI) was induced by ligation of left anterior descending coronary artery with a combination of cryoinjury. Ten days after the MI, cells obtained from autologous femoral arteries were injected into the injured myocardium of group A, while group B received an injection of only DMEM medium. Clinical, echocardiographic, and histopathologic evaluations were done. As compared to the ninth day values, echocardiography showed a significant improvement in systolic functions and left ventricular (LV) dimensions of the cell-treated group on the 30th day. In the heart biopsy sections of branch-1, the immunostained injected cells were observed to exist closely, suggesting an organization. Cells existing separately and lumen-like structure organizations stained positive with both smooth muscle cell (SMC) alpha-actin and Prussian Blue were also showed in the histological observation of branch-2. Autologous AMICS transplantation seems to be a feasible and efficacious method for cellular cardiomyoplasty in our rabbit model.