A new paradigm for stem cell therapy: Substance-P as a stem cell-stimulating agent

Bone marrow is a reservoir for hematopoietic stem cells, endothelial precursor cells, and bone marrow stromal cells (also generally called mesenchymal stem cells), whose positive role in tissue repair is highly anticipated. In this report, we introduce a novel function of substance-P (SP), an 11-amino-acid peptide, as an injury-inducible messenger to mobilize bone marrow stem cells to the blood and finally to engage in tissue repair. This new drug may substitute for ex vivo cell culture of therapeutic cells by stimulating cell proliferation in the bone marrow in vivo and mobilizing those therapeutic cells to the patient’s own blood stream. Again, the additional role of SP in mitigating inflammation-mediated tissue damage can further rationalize the clinical development of SPpeptide as a stem cell stimulant.     

内皮祖细胞的迁移及对血管修复作用的研究进展

血管内皮损伤及其修复功能发生障碍在心血管疾病的发生发展过程中起着重要作用,内皮祖细胞是干细胞的一种亚型,为内皮细胞的前体细胞,在成年机体内主要定居在骨髓干细胞池中,具有高增殖潜能.多种因素可刺激EPCs从骨髓动员到外周血液,在细胞因子等作用下归巢到血管损伤部位并分化为成熟内皮细胞.本文就骨髓EPCs从动员到分化为内皮细胞过程中不同标志物的表达及可能存在的分子信号机制进行综述.     

Bone marrow-derived cells: the influence of aging and cellular senescence

During the course of an entire lifespan, tissue repair and regeneration is made possible by the presence of adult stem cells. Stem cell expansion, maintenance, and differentiation must be tightly controlled to assure longevity. Hematopoietic stem cells (HSC) are greatly solicited given the daily high blood cell turnover. Moreover, several bone marrow-derived cells including HSC, mesenchymal stromal cells (MSC), and endothelial progenitor cells (EPC) also significantly contribute to peripheral tissue repair and regeneration, including tumor formation. Therefore, factors influencing bone marrow-derived cell proliferation and functions are likely to have a broad impact. Aging has been identified as one of these factors. One hypothesis is that aging directly affects stem cells as a consequence of exhaustive proliferation. Alternatively, it is also possible that aging indirectly affects stem cells by acting on their microenvironment. Cellular senescence is believed to have evolved as a tumor suppressor mechanism capable of arresting growth to reduce risk of malignancy. In opposition to apoptosis, senescent cells accumulate in tissues. Recent evidence suggests their accumulation contributes to the phenotype of aging. Senescence can be activated by both telomere-dependent and telomere-independent pathways. Genetic alteration, genome-wide DNA damage, and oxidative stress are inducers of senescence and have recently been identified as occurring in bone marrow-derived cells. Below is a review of the link between cellular senescence, aging, and bone marrow-derived cells, and the possible consequences aging may have on bone marrow trans plantation procedures and emerging marrow-derived cell-based therapies.     

Effect of paclitaxel and mesenchymal stem cells seeding on ex vivo vascular endothelial repair and smooth muscle cells growth

Late thrombosis and neointima proliferation after paclitaxel-eluting stents implanting may be related to delayed endothelial cells (ECs) regeneration. This study was to investigate whether mesenchymal stem cells (MSCs) seeding can accelerate endothelial repair and attenuate late smooth muscle cells (SMCs) proliferation after paclitaxel intervention. An ex vivo model of endothelium repair was developed in which rabbit smooth muscle cells were inoculated in the upper chamber and rabbit endothelial cells/human mesenchymal stem cells in the lower chamber of a co-culture system. Paclitaxel (10 nmol/L, 20 min) inhibited smooth muscle cell growth of the confluent endothelial cell group during the observed period. However, increased smooth muscle cells growth was observed in the proliferative endothelial cells group 10 days after paclitaxel intervention. Mesenchymal stem cell seeding inhibited late smooth muscle cell growth incompatible with the effect of proliferative endothelial cells. However, no inhibition on smooth muscle cell growth was observed with mesenchymal stem cell seeding in comparison to the effect of confluent endothelial cells. No vWF but Flk-1 protein was observed in the 25.71% of mesenchymal stem cells after having been co-cultured with rabbit endothelial cells for 5 days. These results indicate that late smooth muscle cell proliferation is closely related to the delayed endothelial cells regeneration after paclitaxel application. Mesenchymal stem cell seeding partly attenuates the late smooth muscle cell proliferation. Mesenchymal stem cells co-cultured with mature endothelial cells have the ability to differentiate toward endothelial cells.     

The pleiotropic effects of ARB in vascular endothelial progenitor cells

Angiotensin II regulates blood pressure and contributes to endothelial dysfunction and the progression of atherosclerosis. Bone marrow-derived endothelial progenitor cells (EPCs) in peripheral blood contribute to postnatal vessel repair and neovascularization. Impaired EPC function in patients with hypertension and diabetes inhibits the endogenous repair of vascular lesions and leads to the progression of atherosclerosis. The number of EPCs in peripheral blood is inversely correlated with mortality and the occurrence of cardiovascular events. Angiotensin II-mediated signaling is implicated in oxidative stress, inflammation and insulin resistance, factors that cause EPC dysfunction. Blockade of the angiotensin II type 1 receptor may therefore present a new therapeutic target for enhancing EPC function.     

Role of interleukin-4 in atherosclerosis

Vascular endothelial cell injury or dysfunction has been implicated in the onset and progression of cardiovascular diseases including atherosclerosis. A number of previous studies have demonstrated that the pro-oxidative and pro-inflammatory pathways within vascular endothelium play an important role in the initiation and progression of atherosclerosis. Recent evidence has provided compelling evidence to indicate that interleukin-4 (IL-4) can induce pro-inflammatory environment via oxidative stress-mediated up-regulation of inflammatory mediators such as cytokine, chemokine, and adhesion molecules in vascular endothelial cells. In addition, apoptotic cell death within vascular endothelium has been hypothesized to be involved in the development of atherosclerosis. Emerging evidence has demonstrated that IL-4 can induce apoptosis of human vascular endothelial cells through the caspase-3-dependent pathway, suggesting that IL-4 can increase endothelial cell turnover by accelerated apoptosis, the event which may cause the dysfunction of the vascular endothelium. These studies will have a high probability of revealing new directions that lead to the development of clinical strategies toward the prevention and/or treatment for individuals with inflammatory vascular diseases including atherosclerosis.     

Platelet interaction with progenitor cells: vascular regeneration or inquiry?

Increasing evidence supports the role of stem and progenitor cells in vascular regeneration or injury. Following tissue ischemia, progenitor cells are mobilized from their bone marrow or peripheral niches into circulation, adhere at sites of vascular lesion and differentiate into a variety of mature cell types according to their origin and the local environment. Impairment in this pathophysiological process due to either low numbers of circulating progenitor cells or dysfunctional progenitor cells leads to inadequate vascular repair and upon co-existence with different cardiovascular risk factors to vascular injury and atherosclerosis. Vascular repair is a complex process which includes mobilization, chemotaxis, adhesion, proliferation and differentiation of progenitor cells. The common cardiovascular risk factors can impair this process resulting into inhibition of vascular healing and enhancement of inflammatory pathways which ultimately leads to atherosclerosis. Although homing of progenitor cells into bone marrow has been extensively studied, domiciliation of precursor cells into peripheral tissues and differentiation into mature cells are poorly understood so far. Recently, the role of platelets in domiciliation and subsequent differentiation of progenitor cells has been highlighted. Adherent platelets recruit circulating progenitor cells in vitro and in vivo and induce differentiation of the latter into endothelial cells or macrophages and foam cells. Although further studies are needed to describe the mechanisms that lie underneath these observations, it seems that platelet interaction with progenitor cells is an essential step in both vascular regeneration and injury.     

Endothelial progenitors in vascular repair and angiogenesis: how many are needed and what to do?

Defects in the regulation of neo blood vessel growth (angiogenesis) or in vessel repair are major complications in many diseases, such as cancer, diabetes, atherosclerosis and myocardial infarction. In these diseases it was shown that the number of circulating endothelial progenitor cells (EPC) was altered. This has been associated with the angiogenic status and patient prognosis. However, the regulation of angiogenesis depends not only on the number of circulating EPC but also on their functions. EPC are bone marrow derived cells that are recruited into the peripheral blood in situations of vascular repair/angiogenesis or vascular stress. EPC are believed to exert their function using mainly two strategies: activating locally the endothelial cells and/or differentiating into mature endothelial cells that integrate the damaged vessels. To do this, EPC must home to "angiogenic active" sites, adhere to the activated/damaged endothelial cells or to the extracellular matrix and participate in the endothelial activation/repair process. In vitro and in vivo experiments using animal models revealed the importance of various signalling pathways in these processes and, in patients, new therapeutic strategies are being developed based on the specific functions of EPC. Although the role of EPC in vessel repair in disease is not totally understood, it becomes clear that the activation state of these cells is critical for the vessel repair process. Our previous work generated a detailed gene expression profile of EPC during the endothelial differentiation process in vitro. With this information, it has been possible to identify numerous molecular targets crucial for EPC differentiation and function and to test their involvement in EPC function during wound healing or tumor angiogenesis. The importance of EPC identification, activation state and function in vascular repair and in angiogenesis in disease will be discussed in this review.     

干细胞在子宫内膜损伤修复中的研究进展

临床实践中,子宫内膜损伤与频繁的宫腔操作史、感染及部分药物的使用密切相关.严重者可能会引起子宫内膜基底层的损伤,影响子宫内膜上皮细胞和损伤血管的再生,从而导致子宫内膜修复困难.临床上可表现为月经减少,闭经,不孕,习惯性流产,早产和胎盘异常等.对于重度子宫内膜损伤的治疗是临床上较为棘手的问题,近年来国内外学者研究发现干细胞移植在子宫内膜损伤修复方面具有重要作用,细胞治疗为子宫内膜损伤后修复提供了新的思路和方向.     

Involvement of marrow-derived endothelial cells in vascularization

Until recently, the adult neovasculature was thought to arise only through angiogenesis, the mechanism by which new blood vessels form from preexisting vessels through endothelial cell migration and proliferation. However, recent studies have provided evidence that postnatal neovasculature can also arise though vasculogenesis, a process by which endothelial progenitor cells are recruited and differentiate into mature endothelial cells to form new blood vessels. Evidence for the existence of endothelial progenitors has come from studies demonstrating the ability of bone marrow-derived cells to incorporate into adult vasculature. However, the exact nature of endothelial progenitor cells remains controversial. Because of the lack of definitive markers of endothelial progenitors, the in vivo contribution of progenitor cells to physiological and pathological neovascularization remains unclear. Early studies reported that endothelial progenitor cells actively integrate into the adult vasculature and are critical in the development of many types of vascular-dependent disorders such as neoplastic progression. Moreover, it has been suggested that endothelial progenitor cells can be used as a therapeutic strategy aimed at promoting vascular growth in a variety of ischemic diseases. However, increasing numbers of studies have reported no clear contribution of endothelial progenitors in physiological or pathological angiogenesis. In this chapter, we discuss the origin of the endothelial progenitor cell in the embryo and adult, and we discuss the cell's link to the primitive hematopoietic stem cell. We also review the potential significance of endothelial progenitor cells in the formation of a postnatal vascular network and discuss the factors that may account for the current lack of consensus of the scientific community on this important issue.     

Stem cell-derived endothelial cells for cardiovascular disease: a therapeutic perspective

Stem cell therapy and organ regeneration are therapeutic approaches that will, we suggest, become mainstream for the treatment of human disease. Endothelial cells, which line the luminal surface of every vessel in the body, are essential components in any organ regeneration programme. There are a number of potentially therapeutic endothelial cell types, including embryonic, adult progenitor and induced pluripotent stem cell-derived endothelial cells, as well as host vascular cells. The features (benefits as well as disadvantages) of each cell type that make them potentially useful in therapy are important to consider. The field of stem cell biology is well developed in terms of protocols for generating endothelium. However, where there is a distinct and urgent unmet need for knowledge concerning how the endothelial cells from these different sources function as endothelium and how susceptible they may be to inflammation and atherosclerosis. Furthermore, where stem cells have been used in clinical trials there is little commonality in protocols for deriving the cells (and thereby the specific phenotype of cells used), administering the cells, dosing the cells and/or in assessing efficacy attributed to the cells themselves. This review discusses these and other issues relating to stem cell-derived endothelial cells in cell therapy for cardiovascular disease.     

Oxidative stress on progenitor and stem cells in cardiovascular diseases

There is accumulating evidence that reactive oxygen species (ROS) play major roles in the initiation and progression of cardiovascular dysfunction associated with diseases such as hyperlipidemia, diabetes mellitus, hypertension, ischemic heart disease, and chronic heart failure. ROS produced by migrating inflammatory cells as well as vascular cells (endothelial cells, vascular smooth muscle cells, and adventitial fibroblasts) have distinct functional effects on each cell type. These effects include cell growth, apoptosis, migration, inflammatory gene expression and matrix regulation. ROS, through regulating vascular cell function, can play a central role in normal vascular physiology, and contribute substantially to the development of cardiovascular diseases. Excessive production of ROS is an essential mechanism underlying the pathogenesis of endothelial dysfunction and cardiovascular disease. Stem cells hold great promise for tissue repair and regenerative medicine, and endothelial progenitor cells (EPC) play a significant role in neovascularization of ischemic tissue. Recent studies have shown that cardiovascular risk factors such as hypertension, hypercholesterolemia, diabetes and cigarette smoking are inversely correlated with EPC number and function. Understanding the mechanisms, that regulate EPC function may provide new insights into the pathogenesis of vasculogenesis and may promote development of specific therapies to prevent ROS production and ultimately correct EPC dysfunction. We have demonstrated the angiotensin II receptor blockers improve EPC dysfunction through antioxidative mechanisms. In the present review, we describe our current understanding of the contributions of oxidative stress to progenitor and stem cell dysfunction in cardiovascular disease and focus on the potential mechanisms that underlie oxidative stress-induced damage of progenitor and stem cells.     

Transglutaminase and vascular biology: physiopathologic implications and perspectives for therapeutic interventions

Consistent clinical and experimental evidence points to the involvement of two enzymatic systems (the matrix metalloproteinases-MMPs and the protein crosslinking enzymes transglutaminases) in prominent physiologic roles of endothelium in the maintenance of vascular wall integrity, regulation of blood flow and clotting, and exchange of molecules and cells between the extra- and the intravascular space. These issues are briefly discussed in relation to differentiation of the endothelium within the vascular system, mechanisms of molecular regulation and the effects of their disruption in pathology. While the roles of MMPs are now understood in detail and represent a promising target for pharmacological interventions, much less is known on the roles of transglutaminases in vascular biology. These last enzymes are expressed at extremely high levels in endothelial cells and are involved in cell matrix interactions important to angiogenesis and apoptosis/cell death of endothelial cells, in the control of blood clotting and and in the transfer of molecules and cells across the vascular walls. On the clinical side, these properties are relevant in vascular inflammatory processes, atherosclerosis and tumor metastasis. We summarise the large body of evidence available in this perspective and discuss its implications for the development of new therapeutic strategies.     

Stem cell implantation for myocardial disorders

Cell therapy is currently attracting growing interest as a potential new means of improving the prognosis of patients with heart failure. For practical reasons, autologous skeletal myoblasts have been the first to be tested in clinical trials, but recently cardiovascular researchers has explored many other cell types, including bone marrow cells, endothelial progenitor cells, mesenchymal stem cells, embryonic stem cells, and resident cardiac stem cells. While recent experimental studies and early-phase clinical trials seem to support the concept that cell therapy may enhance cardiac repair, many challenges remain before achieving this goal. Further studies should focus on finding the optimal donor cells for transplantation, the mechanism by which engrafted cells improve cardiac function, controlling the survival and proliferation of transplanted cells, and the development of more efficient cell delivery techniques.     

Stem cell-derived angiogenic/vasculogenic cells: possible therapies for tissue repair and tissue engineering

1. The recent ability to isolate stem cells and study their specific capacity of self-renewal with the formation of different cell types has opened up exciting vistas to help the repair of damaged tissue and even the formation of new tissue. In the present review, we deal with the characteristics and sources that stem cells can be derived and cultured from. 2. We focus on the role that stem cell-derived vascular cells or endothelial progenitor cells (EPC) may play in (re)vascularization of ischaemic and engineered tissues. This so-called vasculogenesis resembles the embryological process in which 'haemangioblasts' differentiate in blood cells, as well as in primitive vessels. Although also derived from the blood-forming bone marrow, in adult life vasculogenic stem cells contribute only little to the regular vascular repair mechanisms: namely (i) angiogenesis (outgrowth of vessels from existing vessels); and (ii) arteriogenesis (monocyte-aided increase in the calibre of existing arteriolar collaterals). 3. Most attempts to increase vascular repair by stem cells involve the use of growth factors, which mobilize stem cells from bone marrow into the blood, sometimes combined with isolation and reinfusion of these cells after ex vivo expansion and differentiation into EPC. 4. Clear improved perfusion of ischaemic sites and new vasculature has been observed in vivo mostly in animal models. Specific homing or administration of these cells and regulated and quantitative expansion and (final) differentiation at these vascular (repair) sites are less studied, but are paramount for efficacy and safety. 5. In conclusion, the use of embryonic stem cells will still encounter ethical objections. Moreover, special attention and measures are needed to cope with the allogeneic barriers that these cells usually encounter. In general, the long and complicated ex vivo cultures to obtain sufficient offspring from the very small numbers of stem cells that can be obtained as starting material will be costly and cumbersome. Both basic research on conceptual matters and cost-effective development of the product itself will have to go a long way before the clinical use of some volume can be expected.     

IBC’s 6th Annual Conference on Angiogenesis: Novel Therapeutic Developments

Angiogenesis is a process that is dependent upon co-ordinate production of angiogenesis stimulatory and inhibitory (angiostatic) molecules. Any imbalance in this regulatory circuit may lead to the development of a number of angiogenesis-mediated diseases. Angiogenesis is a multi-step process including activation, adhesion, migration, proliferation and transmigration of endothelial cells across cell matrices to or from new capillaries and from existing vessels. Angiogenesis is a process involved in the formation of new vessels by sprouting from pre-existing vessels. In contrast, vessel rudiments are sorted by a process termed vasculogenesis. Endothelial heterogeneity and organ specificity might contribute to differences in the response to different anti-angiogenic mechanisms (cultured EC versus microvascular EC isolated from different tissues). Under normal physiological conditions in mature organisms, endothelial cell turnover or angiogenesis is extremely slow (from months to years). However, angiogenesis can be activated for a limited time in certain situations such as wound healing and ovulation. In certain pathological states, such as human metastasis (oncology) and ocular neovascularisation, disorders including diabetic retinopathy and age-related macular degeneration (ophthalmology), there is excessive and sustained angiogenesis. Hence, understanding the mechanisms involved in the regulation of angiogenesis could have a major impact in the prevention and treatment of pathological angiogenic processes. Additionally, endothelial cells play a major role in the modelling of blood vessels. The interplay of growth factors, cell adhesion molecules, matrix proteases and specific signal transduction pathways either in the maintenance of the quiescent state or in the reactivation of endothelial cells is critical in physiological and pathological angiogenic processes.     

Concerns and hopes for stem cell therapy in cardiology: focus on endothelial progenitor cells

The crucial role played by the endothelium in cardiovascular disorders has been repetitively recognised. Endothelium injury has been implicated in atherosclerosis, thrombosis, hypertension and other cardiovascular diseases. Recently, however, research has undertaken a new avenue. As mature endothelial cells posses limited regenerative capacities, the interest has been switched to the circulating endothelial progenitor cells (EPCs). Indeed, the scientific community has made progress in understanding the role of EPCs in the maintenance of endothelial integrity and function as well as post natal neovascularisation. It has been suggested that these cells are able to home in the site of heart injury / damage and that they might take part in angiogenesis, giving hope for new treatment opportunities. There is evidence that reduced availability of EPCs or impairment of their function is associated with more severe CV disease and to comorbid risk factors. Different current drug regimes are able to influence bone marrow production and release of EPCs and several growth factors are considered for possible useful new therapeutic approaches. Thus, many studies into the potential use of EPCs in the clinical setting have recently been conducted with conflicting results. The goal of this review article is to discuss current therapies to regenerate new vessels and therefore to enhance myocardial function. The article overviews the search strategy and the pathophysiological aspects behind this therapy, consider the target currently under investigation and set the stage for new ideas.     

Cellular and molecular mechanisms of vascular injury in diabetes--part II: cellular mechanisms and therapeutic targets

Although the mechanisms by which insulin-resistance and hyperglycemia lead to cardiovascular disease are still incompletely understood, all mechanisms apparently converge on the vessel wall and the endothelium as a common disease target. Endothelial cells play a crucial role in vascular homeostasis, providing a functional barrier and modulating several signals involved in vasomotion, as well as antiplatelet, anti-inflammatory, anti-proliferative, and anti-oxidant properties of the vessel wall. Endothelial cell dysfunction occurs early in diabetes and insulin resistance states. Since atherosclerosis may result from an imbalance between the magnitude of vascular injury and the capacity of repair, a role has been recently postulated for a defective mobilization of vascular progenitors, including endothelial progenitor cells, in the pathogenesis of vascular disease. Here we summarize the evidence for such an occurrence. We also here highlight how new insights into pathways of vascular damage in diabetes may indicate new targets for preventive and treatment strategies.     

Potential target sites to modulate vascular endothelial dysfunction: current perspectives and future directions

Endothelium is innermost lining of the blood vessel and it regulates the vascular tone. It plays a critical role in the mechanics of blood flow, regulation of coagulation, leukocyte adhesion, vascular smooth muscle cell (VSMC) growth and immune function. Endothelial dysfunction results in reduced vasodilatation, proinflammatory state and prothrombotic properties. Various experimental evidences revealed that reduced nitric oxide production and increased oxidative stress lead to vascular endothelial dysfunction (VED). Environmental factors such as cigarette smoking, alcohol consumption and exposure to arsenic play a critical role in the development of endothelial dysfunction. Vascular endothelial dysfunction is a hallmark for various cardiovascular disorders such as hypertension, atherosclerosis, heart failure, myocardial infarction and stroke. However, the pathological mechanism involved in the vascular endothelial dysfunction is poorly understood. The present review delineates various potential target sites for vascular endothelial dysfunction, which may open a new vista for exploring novel pharmacological agents to treat various cardiovascular disorders.