Adult neural stem cells: response to stroke injury and potential for therapeutic applications

The plasticity of neural stem/progenitor cells allows a variety of different responses to many environmental cues. In the past decade, significant research has gone into understanding the regulation of neural stem/progenitor cell properties, because of their promise for cell replacement therapies in adult neurological diseases. Both endogenous and grafted neural stem/progenitor cells are known to have the ability to migrate long distances to lesioned sites after brain injury and differentiate into new neurons. Several chemokines and growth factors, including stromal cell-derived factor-1 and vascular endothelial growth factor, have been shown to stimulate the proliferation, differentiation, and migration of neural stem/progenitor cells, and investigators have now begun to identify the critical downstream effectors and signaling mechanisms that regulate these processes. Both our own lab and others have shown that the extracellular matrix and matrix remodeling factors play a critical role in directing cell differentiation and migration of adult neural stem/progenitor cells within injured sites. Identification of these and other molecular pathways involved in stem cell homing into ischemic areas is vital for the development of new treatments. To ensure the best functional recovery, regenerative therapy may require the application of a combination approach that includes cell replacement, trophic support, and neural protection. Here we review the current state of our knowledge about endogenous adult and exogenous neural stem/progenitor cells as potential therapeutic agents for central nervous system injuries.     

脂肪干细胞治疗心肌梗死的机制与新策略

介绍脂肪干细胞（ADSCs）治疗心肌梗死机制及用于提高心肌梗死治疗效果的新策略。广泛查阅近年关于ADSCs用于治疗心肌梗死的基础与临床实验研究文献,并进行整理、综合与分析。ADSCs移植治疗心肌梗死的机制研究取得了一定的进展,其机制主要包括分化为心肌细胞、参与梗死区血管形成、通过旁分泌功能改善梗死区微环境等。对ADSCs进行缺氧耐受预处理、使用新型生物材料、联合细胞因子以及药物等,可以大大提高移植细胞的存活率,促进细胞的增殖与分化,改善心肌梗死治疗效果,加快心脏功能的恢复。ADSCs可能通过多种机制发挥治疗心肌梗死的作用,进一步提高移植细胞成活率和性能稳定性是增加ADSCs治疗心肌梗死效果的关键。随着研究的不断深入,ADSCs可能为未来心肌梗死的临床治疗带来新的希望。     

Comparison of mesenchymal stem cells from adipose tissue and bone marrow for ischemic stroke therapy

Background aimsTransplantation of mesenchymal stromal cells (MSC) derived from bone marrow (BM) or adipose tissue is expected to become a cell therapy for stroke. The present study compared the therapeutic potential of adipose-derived stem cells (ASC) with that of BM-derived stem cells (BMSC) in a murine stroke model.MethodsASC and BMSC were isolated from age-matched C57BL/6J mice. These MSC were analyzed for growth kinetics and their capacity to secrete trophic factors and differentiate toward neural and vascular cell lineages in vitro. For in vivo study, ASC or BMSC were administrated intravenously into recipient mice (1 × 10⁵ cells/mouse) soon after reperfusion following a 90-min middle cerebral artery occlusion. Neurologic deficits, the degree of infarction, expression of factors in the brain, and the fate of the injected cells were observed.ResultsASC showed higher proliferative activity with greater production of vascular endothelial cell growth factor (VEGF) and hepatocyte growth factor (HGF) than BMSC. Furthermore, in vitro conditions allowed ASC to differentiate into neural, glial and vascular endothelial cells. ASC administration showed remarkable attenuation of ischemic damage, although the ASC were not yet fully incorporated into the infarct area. Nonetheless, the expression of HGF and angiopoietin-1 in ischemic brain tissue was significantly increased in ASC-treated mice compared with the BMSC group.ConclusionsCompared with BMSC, ASC have great advantages for cell preparation because of easier and safer access to adipose tissue. Taken together, our findings suggest that ASC would be a more preferable source for cell therapy for brain ischemia than BMSC.     

The application of stem cells in the treatment of ischemic diseases

Ischemia causes oxygen deprivation, cell injury and related organ dysfunction. Although ischemic injury may be local, it involves many biochemical changes in different cell types. The ability of stem cells to differentiate into different cell lineages provides the possibility of their use in treating a variety of diseases requiring tissue repair or reconstitution, such as stroke, ischemic retinopathy, myocardial infarction, ischemic disorders of the liver, ischemic renal failure, and ischemic limb dysfunction. Several cell types including embryonic stem cells, various progenitor and stem cells of hematopoietic or mesenchymal origin have been used in attempts to reconstitute injured tissue. Xenologous or autologous stem cells may be administered either through the peripheral vascular system or directly by regional injection. The stem cells are then guided to the infarct site by homing signals. Either by cell differentiation or paracrine effects, stem cells or progenitor cells participate in the reconstruction of a favorable microenvironment resulting in neovascularization and tissue regeneration that eventually improve the physiological function of organs with ischemic damage.     

Cancer stem cells: redefining the paradigm of cancer treatment strategies

Cancer has been known to arise from long-lived cells in the body and to possess properties in common with undifferentiated, embryonic cells. Recent findings of a population of cells in solid tumors resembling stem cells supports a stem cell model of cancer. A scheme in which all cancers initiate from "activated' stem cells helps bring together data from genetic, cell biology, and epidemiology studies. Cancer can arise from embryonic cells in the case of childhood tumors; hormone-activated stem cells in the case of breast cancer; and following chronic activation of stem cells caused by tissue damage. This scheme helps explain the failure of many cancer therapies, points out deficiencies in certain research approaches, and focuses the problem on a subset of cells that can be explicitly targeted, leading to more efficient therapy.     

Novel multi-functional nitrones for treatment of ischemic stroke

Ischemic stroke resulting from obstruction of blood vessels is an enormous public health problem with urgent need for effective therapy. The co-administration of thrombolytic/antiplatelet agent and neuroprotective agent improves therapeutic efficacy and agent possessing both thrombolytic/antiplatelet and antiradical activities provides a promising strategy for the treatment of ischemic stroke. We have previously reported a novel compound, namely TBN, possessing both antiplatelet and antiradical activities, showed significant neuroprotective effect in a rat stroke model. We herein report synthesis of a series of new pyrazine derivatives, and evaluation of their biological activities. Their mechanisms of action were also investigated. Among these new derivatives, compound 21, armed with two nitrone moieties, showed the greatest neuroprotective effects in vitro and in vivo. Compound 21 significantly inhibited ADP-induced platelet aggregation. In a cell free antiradical assay, compound 21 was the most effective agent in scavenging the three most damaging radicals, namely (·)OH, O(2)(·-) and ONOO(-).     

Adult stem cells and multiple sclerosis

Multiple sclerosis (MS) is a common neurological disease and a major cause of disability, particularly affecting young adults. It is characterized by patches of damage occurring throughout the brain and spinal cord, with loss of myelin sheaths - the insulating material around nerve fibres that allows normal conduction of nerve impulses - accompanied by loss of cells that make myelin (oligodendrocytes). In addition, we now know that there is damage to nerve cells (neurones) and their fibres (axons) too, and that this occurs both within these discrete patches and in tissue between them. The cause of MS remains unknown, but an autoimmune reaction against oligodendrocytes and myelin is generally assumed to play a major role, and early acute MS lesions almost invariably show prominent inflammation. Efforts to develop cell therapy in MS have long been directed towards directly implanting cells capable of replacing lost oligodendrocytes and regenerating myelin sheaths. Accordingly, the advent of techniques to generate large numbers of oligodendrocytes from embryonic stem cells appeared a significant step towards new stem cell treatments for MS; while the emerging consensus that adult stem cells from, for example, the bone marrow had far less potential to turn into oligodendrocytes was thought to cast doubt on their potential value in this disease. A number of scientific and medical concerns, not least the risk of tumour formation associated with embryonic stem cells, have however, prevented any possible clinical testing of these cells in patients. More recently, increasing understanding of the complexity of tissue damage in MS has emphasized that successful cell therapy may need to achieve far more than simply offering a source of replacement myelin-forming cells. The many and varied reparative properties of bone marrow-derived (mesenchymal) stem cells may well offer new and attractive possibilities for developing cell-based treatments for this difficult and disabling condition.     

Antioxidant strategies in the treatment of stroke

Excessive production of free radicals is known to lead to cell injury in a variety of diseases, such as cerebral ischemia. In this review, we describe some of the numerous studies that have examined this oxidative stress and the efficiency of antioxidant strategies in focal cerebral ischemia. Besides using genetically modified mice, these strategies can be divided into three groups: (1) inhibition of free radical production, (2) scavenging of free radicals, and (3) increase of free radical degradation by using agents mimicking the enzymatic activity of endogenous antioxidants. Finally, the clinical trials that have tested or are currently testing the efficiency of antioxidants in patients suffering from stroke are reviewed. The results presented here lead us to consider that antioxidants are very promising drugs for the treatment of ischemic stroke.     

The use of gating technology in bioengineering insulin-secreting cells from embryonic stem cells

Embryonic stem cells display the ability to differentiate in vitro into a variety of cell types. This process is induced by embryoid body formation, addition of several soluble growth factors to the culture medium and other strategies. However, none of the used factors is capable to drive differentiation to only one specific celltype. The use of gating technology has allowed to partially overcome this problem. The rational behind this technique is based on the transfection of stem cells with a transgene carrying expression cassettes for a cell type specific promoter, regulating expression ofa selectable marker to select one cell lineage from other cell lineages.Using this system, we have obtained insulin-secreting cells by transfecting mouse embryonic stem cells with a DNA construct providing resistance to neomycin under the control of the regulatory regions of the human insulin gene. Furthermore, gating technology has been successfully used to isolate other cell types such as cardiomyocytes and neural precursors from undifferentiated embryonic stem cells. This review focuses on the possibilities offered by this technology in embryonic stem cell bioengineering, mainly to obtain insulin-secreting cells. Advantages and considerations of this selection system will be also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some epidemiologic and clinical problems in ischemic cerebral stroke

The study involved 739 patients with the ischemic cerebral stroke into two groups: with reversible and irreversible ischemic cerebral stroke. General characteristics of patients (incidence, sex, age etc.) was similar to the characteristics of patients from other centres. Morbidity rate for ischemic cerebral strokes was 93.9, including reversible stroke 21.3 and other 72.6; mortality factor 47.2, and mortality rate 29.6%. An increase in morbidity for irreversible stroke in women over 80 years of age is striking. The authors suggest that the classification of cerebral strokes should include reversible strokes whereas progressive stroke should not be considered distinguished entity.     

Antioxidative and thrombolytic TMP nitrone for treatment of ischemic stroke

Ischemic stroke results from brain blood vessel blockage by thrombus, and produces neuronal cell damage and death. While thrombolytic therapy with tPA has achieved some success in clinic, the strategy of using neuroprotective agents to treat ischemic stroke has been disappointing thus far. In the present work, we synthesized TBN, a derivative of the clinically useful stroke drug TMP armed with a powerful free radical-scavenging nitrone moiety. TBN retains the thrombolytic activity of the parent TMP and possesses strong antioxidative properties. TBN demonstrates significant activity in the rat MCAo stroke model. The results suggest that design of molecules possessing both thrombolytic and neuroprotective properties may be a novel strategy for effective stroke therapeutics.     

Clinical strategies for expansion of haematopoietic stem cells

Haematopoietic stem cells (HSCs) give rise to all blood and immune cells and are used in clinical transplantation protocols to treat a wide variety of diseases. The ability to increase the number of HSCs either in vivo or in vitro would provide new treatment options, but the amplification of HSCs has been difficult to achieve. Recent insights into the mechanisms of HSC self-renewal now make the amplification of HSCs a plausible clinical goal. This article reviews the molecular mechanisms that control HSC numbers and discusses how these can be modulated to increase the number of HSCs. Clinical applications of HSC expansion are then discussed for their potential to address the current limitations of HSC transplantation.     

Statins in prevention and treatment of ischemic stroke

Based on the published data, including the results of large-scale, randomized, placebo-controlled trials, the article presents current strategies for the use of statins in primary and secondary prevention of ischemic stroke. Special attention is paid to the efficacy and advanced applications of statins in acute stroke. Based on the gross data, recommendations for the use of statins in prevention and treatment of ischemic stroke are presented.     

Recovery of neurological function of ischemic stroke by application of conditioned medium of bone marrow mesenchymal stem cells derived from normal and cerebral ischemia rats

Background

Several lines of evidence have demonstrated that bone marrow-derived mesenchymal stem cells (BM-MSC) release bioactive factors and provide neuroprotection for CNS injury. However, it remains elusive whether BM-MSC derived from healthy donors or stroke patients provides equal therapeutic potential. The present work aims to characterize BM-MSC prepared from normal healthy rats (NormBM-MSC) and cerebral ischemia rats (IschBM-MSC), and examine the effects of their conditioned medium (Cm) on ischemic stroke animal model.

Results

Isolated NormBM-MSC or IschBM-MSC formed fibroblastic like morphology and expressed CD29, CD90 and CD44 but failed to express the hematopoietic marker CD34. The number of colony formation of BM-MSC was more abundant in IschBM-MSC than in NormBM-MSC. This is in contrast to the amount of Ficoll-fractionated mononuclear cells from normal donor and ischemic rats. The effect of cm of BM-MSC was further examined in cultures and in middle cerebral artery occlusion (MCAo) animal model. Both NormBM-MSC Cm and IschBM-MSC Cm effectively increased neuronal connection and survival in mixed neuron-glial cultures. In vivo, intravenous infusion of NormBM-MSC Cm and IschBM-MSC Cm after stroke onset remarkably improved functional recovery. Furthermore, NormBM-MSC Cm and IschBM-MSC Cm increased neurogenesis and attenuated microglia/ macrophage infiltration in MCAo rat brains.

Conclusions

Our data suggest equal effectiveness of BM-MSC Cm derived from ischemic animals or from a normal population. Our results thus revealed the potential of BM-MSC Cm on treatment of ischemic stroke.     

Mesenchymal stem cells: therapeutic outlook for stroke

Adult bone marrow-derived mesenchymal stem cells (MSCs) display a spectrum of functional properties. Transplantation of these cells improves clinical outcome in models of cerebral ischemia and spinal cord injury via mechanisms that may include replacement of damaged cells, neuroprotective effects, induction of axonal sprouting, and neovascularization. Therapeutic effects have been reported in animal models of stroke after intravenous delivery of MSCs, including those derived from adult human bone marrow. Initial clinical studies on intravenously delivered MSCs have now been completed in human subjects with stroke. Here, we review the reparative and protective properties of transplanted MSCs in stroke models, describe initial human studies on intravenous MSC delivery in stroke, and provide a perspective on prospects for future progress with MSCs.     

Adult reserve stem cells and their potential for tissue engineering

Tissue restoration is the process whereby multiple damaged cell types are replaced to restore the histoarchitecture and function to the tissue. Several theories, have been proposed to explain the phenomenon of tissue restoration in amphibians and in animals belonging to higher order. These theories include dedifferentiation of damaged tissues, transdifferentiation of lineage-committed progenitor cells, and activation of reserve, precursor cells. Studies by Young et al. and others demonstrated that connective tissue compartments throughout postnatal individuals contain reserve precursor cells. Subsequent repetitive single cell-cloning and cell-sorting studies revealed that these reserve precursor cells consisted of multiple populations of cells, including, tissue-specific progenitor cells, germ-layer lineage stem cells, and pluripotent stem cells. Tissue-specific progenitor cells display various capacities for differentiation, ranging from unipotency (forming a single cell type) to multipotency (forming multiple cell types). However, all progenitor cells demonstrate a finite life span of 50 to 70 population doublings before programmed cell senescence and cell death occurs. Germ-layer lineage stem cells can form a wider range of cell types than a progenitor cell. An individual germ-layer lineage stem cell can form all cells types within its respective germ-layer lineage (i.e., ectoderm, mesoderm, or endoderm). Pluripotent stem cells can form a wider range of cell types than a single germ-layer lineage stem cell. A single pluripotent stem cell can form cells belonging to all three germ layer lineages. Both germ-layer lineage stem cells and pluripotent stem cells exhibit extended capabilities for self-renewal, far surpassing the limited life span of progenitor cells (50–70 population doublings). The authors propose that the activation of quiescent tissue-specific progenitor cells, germ-layer lineage stem cells, and/or pluripotent stem cells may be a potential explanation, along with dedifferentiation and transdifferentiation, for the process of tissue restoration. Several model systems are currently being investigated to determine the possibilities of using these adult quiescent reserve precursor cells for tissue engineering.     

Adult stem cells underlying lung regeneration

Despite the massive toll in human suffering imparted by degenerative lung disease, including COPD, idiopathic pulmonary fibrosis and ARDS, the scientific community has been surprisingly agnostic regarding the potential of lung tissue, and in particular the alveoli, to regenerate. However, there is circumstantial evidence in humans and direct evidence in mice that ARDS triggers robust regeneration of lung tissue rather than irreversible fibrosis. The stem cells responsible for this remarkable regenerative process has garnered tremendous attention, most recently yielding a defined set of cloned human airway stem cells marked by p63 expression but with distinct commitment to differentiated cell types typical of the upper or lower airways, the latter of which include alveoli-like structures in vitro and in vivo. These recent advances in lung regeneration and distal airway stem cells and the potential of associated soluble factors in regeneration must be harnessed for therapeutic options in chronic lung disease.     

Adult stem cells underlying lung regeneration

Despite the massive toll in human suffering imparted by degenerative lung disease, including COPD, idiopathic pulmonary fibrosis and ARDS, the scientific community has been surprisingly agnostic regarding the potential of lung tissue and, in particular, the alveoli, to regenerate. However, there is circumstantial evidence in humans and direct evidence in mice that ARDS triggers robust regeneration of lung tissue rather than irreversible fibrosis. The stem cells responsible for this remarkable regenerative process has garnered tremendous attention, most recently yielding a defined set of cloned human airway stem cells marked by p63 expression but with distinct commitment to differentiated cell types typical of the upper or lower airways, the latter of which include alveoli-like structures in vitro and in vivo. These recent advances in lung regeneration and distal airway stem cells and the potential of associated soluble factors in regeneration must be harnessed for therapeutic options in chronic lung disease.Key words: ARDs, lung regeneration, lung stem cells, influenza, COPD, pulmonary fibrosis