Neuroectodermal and microglial differentiation of bone marrow cells in the mouse spinal cord and sensory ganglia

Combined administration of platelet rich plasma and autologous bone marrow aspirate concentrate for spinal cord injury: a descriptive case series

Administration of platelet rich plasma (PRP) and bone marrow aspirate concentrate (BMAC) has shown some promise in the treatment of neurological conditions; however, there is limited information on combined administration. As such, the purpose of this study was to assess safety and functional outcomes for patients administered combined autologous PRP and BMAC for spinal cord injury (SCI). This retrospective case series included seven patients who received combined treatment of autologous PRP and BMAC via intravenous and intrathecal administration as salvage therapy for SCI. Patients were reviewed for adverse reactions and clinical outcomes using the Oswestry Disability Index (ODI) for up to 1 year, as permitted by availability of follow-up data. Injury levels ranged from C3 through T11, and elapsed time between injury and salvage therapy ranged from 2.4 months to 6.2 years. Post-procedure complications were mild and rare, consisting only of self-limited headache and subjective memory impairment in one patient. Four patients experienced severe disability prior to PRP combined with BMAC injection, as evidenced by high (> 48/100) Oswestry Disability Index scores. Longitudinal Oswestry Disability Index scores for two patients with incomplete SCI at C6 and C7, both of whom had cervical spine injuries, demonstrated a decrease of 28–40% following salvage therapy, representing an improvement from severe to minimal disability. In conclusion, intrathecal/intravenous co-administration of PRP and BMAC resulted in no significant complications and may have had some clinical benefits. Larger clinical studies are needed to further test this method of treatment for patients with SCI who otherwise have limited meaningful treatment options. This study was reviewed and approved by the OhioHealth Institutional Review Board (IRB No. 1204946) on May 16, 2018.

The impact of mouse strain-specific spatial and temporal immune responses on the progression of neuropathic pain

The present study was designed to investigate the correlation between the spatial and temporal aspects of immune responses and genetic heterogeneity in the progression of peripheral neuropathic pain. To address this issue, we first screened four inbred mouse strains (C57BL/6J, C3H/He, DBA/2, and A/J mice) to identify high- and low-responder strains to mechanical hypersensitivity induced by partial sciatic nerve ligation (pSNL). Among these strains, the C57BL/6J strain showed the highest vulnerability to pSNL-induced mechanical hypersensitivity, whereas the C3H/HeSlc strain was most resistant. C3H/HeSlc mice exhibited a significant increase in CD206-immunoreactivity (anti-inflammatory macrophages) in the dorsal root ganglia (DRG) at 3 and 7 days, and lower Iba1-immunoreactivity (microglia) in the spinal cord from 3 to 14 days after pSNL than C57BL/6J mice. These phenomena might be associated with a decrease in the production of inflammatory factors (interleukin-1β, interleukin-6, and CX3CL1) in the DRG and the poor responsiveness of spinal microglia (i.e. microglial production of IL1β, CCL2, and TNFα) against CX3CL1 in C3H/HeSlc mice. Behavioral experiments using bone marrow (BM) chimeric mice derived by crossing C3H/HeSlc and C57BL/6J strains showed that the strength of mechanical hypersensitivity 3 days following pSNL was inversely correlated with the increase in the ratio of anti-inflammatory/pro-inflammatory DRG macrophages, which was based on the BM-derived hematopoietic cells from donor mice. By contrast, the intensity of Iba1-immunoreactivity (microglia) in the spinal cord was dependent on the phenotypes of recipient mice, but not affected by the phenotypes of BM-derived donor hematopoietic cells. These findings suggest that the strain-specific aspects of DRG macrophages and spinal microglia might be related to the early and late phases of pSNL-induced mechanical hypersensitivity, respectively. This study presents a greater understanding of the differences in neuropathic pain among genetically heterogeneous inbred mouse strains, and provides further insights into the spatial and temporal roles of the immune system in the pathogenesis of neuropathic pain.

Biomaterial-Supported Cell Transplantation Treatments for Spinal Cord Injury: Challenges and Perspectives

Spinal cord injury (SCI), resulting in para- and tetraplegia caused by the partial or complete disruption of descending motor and ascending sensory neurons, represents a complex neurological condition that remains incurable. Following SCI, numerous obstacles comprising of the loss of neural tissue (neurons, astrocytes, and oligodendrocytes), formation of a cavity, inflammation, loss of neuronal circuitry and function must be overcome. Given the multifaceted primary and secondary injury events that occur with SCI treatment options are likely to require combinatorial therapies. While several methods have been explored, only the intersection of two, cell transplantation and biomaterial implantation, will be addressed in detail here. Owing to the constant advance of cell culture technologies, cell-based transplantation has come to the forefront of SCI treatment in order to replace/protect damaged tissue and provide physical as well as trophic support for axonal regrowth. Biomaterial scaffolds provide cells with a protected environment from the surrounding lesion, in addition to bridging extensive damage and providing physical and directional support for axonal regrowth. Moreover, in this combinatorial approach cell transplantation improves scaffold integration and therefore regenerative growth potential. Here, we review the advances in combinatorial therapies of Schwann cells (SCs), astrocytes, olfactory ensheathing cells (OECs), mesenchymal stem cells, as well as neural stem and progenitor cells (NSPCs) with various biomaterial scaffolds.

Bone Marrow Stromal Cells for Repair of the Spinal Cord: Towards Clinical Application

Stem cells have been recognized and intensively studied for their potential use in restorative approaches for degenerative diseases and traumatic injuries. In the central nervous system (CNS), stem cell-based strategies have been proposed to replace lost neurons in degenerative diseases such as Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis (Lou Gehrig's disease), or to replace lost oligodendrocytes in demyelinating diseases such as multiple sclerosis. Stem cells have also been implicated in repair of the adult spinal cord. An impact to the spinal cord results in immediate damage to tissue including blood vessels, causing loss of neurons, astrocytes, and oligodendrocytes. In time, more tissue nearby or away from the injury site is lost due to secondary injury. In case of relatively minor damage to the cord some return of function can be observed, but in most cases the neurological loss is permanent. This review will focus on in vitro and in vivo studies on the use of bone marrow stromal cells (BMSCs), a heterogeneous cell population that includes mesenchymal stem cells, for repair of the spinal cord in experimental injury models and their potential for human application. To optimally benefit from BMSCs for repair of the spinal cord it is imperative to develop in vitro techniques that will generate the desired cell type and/or a large enough number for in vivo transplantation approaches. We will also assess the potential and possible pitfalls for use of BMSCs in humans and ongoing clinical trials.

A Method for Reconstruction of Severely Damaged Spinal Cord using Autologous Hematopoietic Stem Cells and Platelet-rich Protein as a Biological Scaffold

Introduction:

There have been attempts to alter the prognosis of severe spinal cord injury in different centers, but none of which have reliably altered the outcome. Some trials use stem cells (SCs) that produced widely differing results. We hereby add our experience in our center of a surgical reconstruction of the damaged spinal cord using a mixture of SCs and Platelet-Rich Protein (PRP) with fibrin coated as a biological scaffold.

Materials and Methods:

Four cases of severely damaged spinal cord have been operated for neurolysis and reconstruction of the spinal cord using SCs and platelet-rich protein (PRP) with fibrin coated harvested from the peripheral circulation of the patient. PRP serves to maintain the position of the SCs. One milliliter suspension contains an average of 2.8 × 10⁶ of autologous hematopoietic SCs. Patients were intraoperatively monitored by somatosensory evoked potential, motor evoked potentials, and delta wave. They are clinically followed postoperatively and electromyogram was repeated every 2 weeks. Magnetic resonance imaging (MRI) was repeated regularly. The patients are followed up for a period between 2 and 3 years.

Results:

One patient demonstrated motor and objective sensory improvement (P = 0.05), two other patients reported subjective sensory improvement, and the fourth one remained without any improvement (P = 0.1). None of these patients demonstrated any sign of deterioration or complication either on the surgery or on implanting of the SCs. MRI clearly proved that the inserted biological scaffold remained in place of reconstruction.

Conclusion:

SCs may play a role in restoring spinal cord functions. However, the unsolved problems of the use of SCs and related ethical issues should be addressed.

Improvement of Combined FISH and Immunofluorescence to Trace the Fate of Somatic Stem Cells after Transplantation

Fluorescence in situ hybridization (FISH) combined with immunohistochemistry of tissue-specific markers provides a reliable method for characterizing the fate of somatic stem cells in transplantation experiments. Furthermore, the association between FISH and fluorescent gene reporter detection can unravel cell fusion phenomena, which could account for apparent transdifferentiation events. However, despite the widespread use of these techniques, they still require labor-extensive protocol adjustments to achieve correct and satisfactory simultaneous signal detection. In the present paper, we describe an improvement of simultaneous FISH and immunofluorescence detection. We applied this protocol to the identification of transplanted human and mouse hematopoietic stem cells in murine brain and muscle. This technique provides unique opportunities for following the path taken by transplanted cells and their differentiation into mature cell types.

Stem cell injection in the hindlimb skeletal muscle enhances neurorepair in mice with spinal cord injury

AIMS

To develop a low-risk, little-invasive stem cell-based method to treat acute spinal cord injuries. methods: Adult mice were submitted to an incomplete spinal cord injury, and mesenchymal stem cells injected intramuscularly into both hindlimbs. Behavior tests and MRI of the spinal cord were periodically performed for up to 6 months, along with immunohistochemical analysis. Immunohistochemical and PCR analysis of the muscles were used to detect the grafted cells as well as the soluble factors released.

RESULTS

The stem cell-treated mice presented significant improvements in their motor skills 5 months after treatment. Spinal cord repair was detected by magnetic resonance and immunohistochemistry. In the hindlimb muscles, the stem cells activated muscle and motor neuron repair mechanisms, due to the secretion of several neurotrophic factors.

CONCLUSION

Bone marrow mesenchymal stem cell injection into hindlimb muscles stimulates spinal cord repair in acute spinal cord lesions.

Grafted Activated Schwann Cells Support Survival of Injured Rat Spinal Cord White Matter

BACKGROUND AND OBJECTIVE

The influence of cultured Schwann cells on injured spinal cord in rats is examined.

METHODS

Focal injury of spinal cord white matter at the T10 level was produced using our original non-laminectomy method with a high-pressure air stream. Schwann cells from 7-day predegenerated rat sciatic nerves were cultured, transducted with green fluorescent protein and injected into the cisterna magna (experimental group) 3 times: immediately after spinal cord injury and 3 and 7 days later. Neurons in the brainstem and motor cortex were labeled with FluoroGold (FG) delivered caudally from the injury site a week before the end of the experiment. The functional outcome and morphologic features of neuronal survival were analyzed during a 12-week follow-up. The lesions were visualized and analyzed using magnetic resonance imaging. The maximal distance of expansion of implanted cells in the spinal cord was measured and the number of FG-positive neurons in the brain was counted.

RESULTS

Rats treated with Schwann cells presented significant improvement of locomotor performance and spinal cord morphology compared with the control group. The distance covered by Schwann cells was 7 mm from the epicenter of the injury. The number of brainstem and motor cortex FG-positive neurons in the experimental group was significantly higher than in the control group.

CONCLUSIONS

The data show that activated Schwann cells are able to induce the repair of injured spinal cord white matter. The route of application of cells via the cisterna magna seemed to be useful for their delivery in spinal cord injury therapy.

Transplantation of stem cell-derived astrocytes for the treatment of amyotrophic lateral sclerosis and spinal cord injury

Neglected for years, astrocytes are now recognized to fulfill and support many, if not all, homeostatic functions of the healthy central nervous system (CNS). During neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and spinal cord injury (SCI), astrocytes in the vicinity of degenerating areas undergo both morphological and functional changes that might compromise their intrinsic properties. Evidence from human and animal studies show that deficient astrocyte functions or loss-of-astrocytes largely contribute to increased susceptibility to cell death for neurons, oligodendrocytes and axons during ALS and SCI disease progression. Despite exciting advances in experimental CNS repair, most of current approaches that are translated into clinical trials focus on the replacement or support of spinal neurons through stem cell transplantation, while none focus on the specific replacement of astroglial populations. Knowing the important functions carried out by astrocytes in the CNS, astrocyte replacement-based therapies might be a promising approach to alleviate overall astrocyte dysfunction, deliver neurotrophic support to degenerating spinal tissue and stimulate endogenous CNS repair abilities. Enclosed in this review, we gathered experimental evidence that argue in favor of astrocyte transplantation during ALS and SCI. Based on their intrinsic properties and according to the cell type transplanted, astrocyte precursors or stem cell-derived astrocytes promote axonal growth, support mechanisms and cells involved in myelination, are able to modulate the host immune response, deliver neurotrophic factors and provide protective molecules against oxidative or excitotoxic insults, amongst many possible benefits. Embryonic or adult stem cells can even be genetically engineered in order to deliver missing gene products and therefore maximize the chance of neuroprotection and functional recovery. However, before broad clinical translation, further preclinical data on safety, reliability and therapeutic efficiency should be collected. Although several technical challenges need to be overcome, we discuss the major hurdles that have already been met or solved by targeting the astrocyte population in experimental ALS and SCI models and we discuss avenues for future directions based on latest molecular findings regarding astrocyte biology.

Safety and neurological assessments after autologous transplantation of bone marrow mesenchymal stem cells in subjects with chronic spinal cord injury

Introduction

The administration of stem cells holds promise as a potential therapy for spinal cord injury (SCI). Mesenchymal stem cells have advantages for clinical applications, since they can be easily obtained, are suitable for autologous transplantation and have been previously shown to induce regeneration of the spinal cord in experimental settings. Here we evaluated the feasibility, safety and potential efficacy of autologous transplantation of mesenchymal stem cells in subjects with chronic complete SCI.

Method

We conducted a phase I, non-controlled study in 14 subjects of both genders aging between 18 to 65 years, with chronic traumatic SCI (>6 months), at thoracic or lumbar levels, classified as American Spinal Injury Association (ASIA) A - complete injury. Baseline somatosensory evoked potentials (SSEP), spinal magnetic resonance imaging (MRI) and urodynamics were assessed before and after treatment. Pain rating was performed using the McGill Pain Questionnaire and a visual analogue score scale. Bone marrow-derived mesenchymal stem cells were cultured and characterized by flow cytometry, cell differentiation assays and G-band karyotyping. Mesenchymal stem cells were injected directly into the lesion following laminectomy and durotomy.

Results

Cell transplantation was an overall safe and well-tolerated procedure. All subjects displayed variable improvements in tactile sensitivity and eight subjects developed lower limbs motor functional gains, principally in the hip flexors. Seven subjects presented sacral sparing and improved American Spinal Injury Association impairment scale (AIS) grades to B or C – incomplete injury. Nine subjects had improvements in urologic function. One subject presented changes in SSEP 3 and 6 months after mesenchymal stem cells transplantation. Statistically significant correlations between the improvements in neurological function and both injury size and level were found.

Conclusion

Intralesional transplantation of autologous mesenchymal stem cells in subjects with chronic, complete spinal cord injury is safe, feasible, and may promote neurological improvements.

Trial registration

ClinicalTrials.gov NCT01325103 – Registered 28 March 2011

Cell and gene therapy for Friedreich ataxia: progress to date

Neurodegenerative disorders such as Friedreich ataxia (FRDA) present significant challenges in developing effective therapeutic intervention. Current treatments aim to manage symptoms and thus improve quality of life, but none can cure, nor are proven to slow, the neurodegeneration inherent to this disease. The primary clinical features of FRDA include progressive ataxia and shortened life span, with complications of cardiomyopathy being the major cause of death. FRDA is most commonly caused by an expanded GAA trinucleotide repeat in the first intron of FXN that leads to reduced levels of frataxin, a mitochondrial protein important for iron metabolism. The GAA expansion in FRDA does not alter the coding sequence of FXN. It results in reduced production of structurally normal frataxin, and hence any increase in protein level is expected to be therapeutically beneficial. Recently, there has been increased interest in developing novel therapeutic applications like cell and/or gene therapies, and these cutting-edge applications could provide effective treatment options for FRDA. Importantly, since individuals with FRDA produce frataxin at low levels, increased expression should not elicit an immune response. Here we review the advances to date and highlight the future potential for cell and gene therapy to treat this debilitating disease.

Microglia and brain macrophages in the molecular age: from origin to neuropsychiatric disease

Mononuclear phagocytic cells in the CNS used to be defined according to their anatomical location and surface marker expression. Recently, this concept has been challenged by the results of developmental and gene expression profiling studies that have used novel molecular biological tools to unravel the origin of microglia and to define their role as specialized tissue macrophages with long lifespans. Here, we describe how these results have redefined microglia and helped us to understand how different myeloid cell populations operate in the CNS based on their cell-specific gene expression signatures, distinct ontogeny and differential functions. Moreover, we describe the vulnerability of microglia to dysfunction and propose that myelomonocytic cells might be used in the treatment of neurological and psychiatric disorders that are characterized by primary or secondary 'microgliopathy'.

Quo Vadis medycyno regeneracyjna?: Quo Vadis Regenerative Medicine?

There are presented the most important sources of pluripotent stem cells for potential application in the regenerative medicine. This review summarizes also advantages and disadvantages for potential application of these cells in clinical medicine.

Mesenchymal autologous stem cells

The use of cell-based therapies for spinal cord injuries has recently gained prominence as a potential therapy or component of a combination strategy. Experimental and clinical studies have been performed using mesenchymal stem cell therapy to treat spinal cord injuries with encouraging results. However, there have been reports on the adverse effects of these stem cell-based therapies, especially in the context of tumor modulation. This article surveys the literature relevant to the potential of mesenchymal autologous stem cells for spinal cord injuries and their clinical implications.

Potential role of growth factors in the management of spinal cord injury

OBJECTIVE

To review central nervous system growth factors and their therapeutic potential and clinical translation into spinal cord injury (SCI), as well as the challenges that have been encountered during clinical development.

METHODS

A systemic review of the available current and historical literature regarding central nervous system growth factors and clinical trials regarding their use in spinal cord injury was conducted.

RESULTS

The effectiveness of administering growth factors as a potential therapeutic strategy for SCI has been tested with the use of brain-derived neurotrophic factor, glial cell-derived neurotrophic factor, neurotrophin 3, and neurotrophin-4/5. Delivery of growth factors to injured SC has been tested by numerous methods. Unfortunately, most of clinical trials at this time are uncontrolled and have questionable results because of lack of efficacy and/or unacceptable side effects.

CONCLUSIONS

There is promise in the use of specific growth factors therapeutically for SCI. However, more studies involving neuronal regeneration and functional recovery are needed, as well the development of delivery methods that allow sufficient quantity of growth factors while restricting their distribution to target sites.

Comparative effects between bone marrow and mesenchymal stem cell transplantation in GDNF expression and motor function recovery in a motorneuron degenerative mouse model

Motorneuron degenerative diseases, such as amyotrophic lateral sclerosis (ALS), are characterized by the progressive and rapid loss of motor neurons in the brain and spinal cord, leading to paralysis and death. GDNF (glial cell line derived neurotrophic factor) has been previously shown to be capable of protecting motor-neurons in ALS animal models although its delivery to the spinal cord after systemic administration is blocked by the blood brain barrier. Thus, it is necessary to develop new neurotrophic approaches to protect these motor neurons from death. Bone marrow-derived stem cells have been shown to be capable of improving a large variety of neurodegenerative disorders through neurotrophic mediated mechanisms. Here we analyzed the effect of transplanting whole bone marrow or cultured mesenchymal stem cells into the spinal cord of a motor neuron degenerative mouse model. Motor functions were analyzed using various behavior tests for several weeks after transplantation. We observed that bone marrow, and to a lesser degree mesenchymal stem cell, treated mice improved significantly in the motor tests performed, coinciding with a higher GDNF immunoreactivity in the grafted spinal cord. In several cases, the treated spinal cords were extracted, the engrafted bone marrow cells isolated and cultured, and finally re-transplanted into the spleen of immunodeficient mice. Re-grafted cells were detected in the host spleen, bloodstream and bone marrow, demonstrating a phenotypic stability. Thus, bone marrow cells do not suffer significant phenotypic modifications and is an efficient procedure to ameliorate motor-neuron degeneration, making it a possible therapeutic approach.

Pluripotent and multipotent stem cells in adult tissues

One of the most intriguing questions in stem cell biology is whether pluripotent stem cells exist in adult tissues. Several groups of investigators employing i) various isolation protocols, ii) detection of surface markers, and iii) experimental in vitro and in vivo models, have reported the presence of cells that possess a pluripotent character in adult tissues. Such cells were assigned various operational abbreviations and names in the literature that added confusion to the field and raised the basic question of whether these are truly distinct or overlapping populations of the same primitive stem cells. Unfortunately, these cells were never characterized side-by-side to address this important issue. Nevertheless, taking into consideration their common features described in the literature, it is very likely that various investigators have described overlapping populations of developmentally early stem cells that are closely related. These different populations of stem cells will be reviewed in this paper.

Concise review: Bone marrow for the treatment of spinal cord injury: mechanisms and clinical applications

Transplantation of bone marrow stem cells into spinal cord lesions enhances axonal regeneration and promotes functional recovery in animal studies. There are two types of adult bone marrow stem cell; hematopoietic stem cells (HSCs), and mesenchymal stem cells (MSCs). The mechanisms by which HSCs and MSCs might promote spinal cord repair following transplantation have been extensively investigated. The objective of this review is to discuss these mechanisms; we briefly consider the controversial topic of HSC and MSC transdifferentiation into central nervous system cells but focus on the neurotrophic, tissue sparing, and reparative action of MSC grafts in the context of the spinal cord injury (SCI) milieu. We then discuss some of the specific issues related to the translation of HSC and MSC therapies for patients with SCI and present a comprehensive critique of the current bone marrow cell clinical trials for the treatment of SCI to date.

Pivotal role of paracrine effects in stem cell therapies in regenerative medicine: can we translate stem cell-secreted paracrine factors and microvesicles into better therapeutic strategies?

Although regenerative medicine is searching for pluripotent stem cells that could be employed for therapy, various types of more differentiated adult stem and progenitor cells are in meantime being employed in clinical trials to regenerate damaged organs (for example, heart, kidney or neural tissues). It is striking that, for a variety of these cells, the currently observed final outcomes of cellular therapies are often similar. This fact and the lack of convincing documentation for donor-recipient chimerism in treated tissues in most of the studies indicates that a mechanism other than transdifferentiation of cells infused systemically into peripheral blood or injected directly into damaged organs may have an important role. In this review, we will discuss the role of (i) growth factors, cytokines, chemokines and bioactive lipids and (ii) microvesicles (MVs) released from cells employed as cellular therapeutics in regenerative medicine. In particular, stem cells are a rich source of these soluble factors and MVs released from their surface may deliver RNA and microRNA into damaged organs. Based on these phenomena, we suggest that paracrine effects make major contributions in most of the currently reported positive results in clinical trials employing adult stem cells. We will also present possibilities for how these paracrine mechanisms could be exploited in regenerative medicine to achieve better therapeutic outcomes. This approach may yield critical improvements in current cell therapies before true pluripotent stem cells isolated in sufficient quantities from adult tissues and successfully expanded ex vivo will be employed in the clinic.

Autologous mesenchymal stem cells in chronic spinal cord injury

Spinal cord injury (SCI) occurs in the most productive part of life. Treatment options for treatment of chronic SCI are few and have limited impact on clinical outcome. Central nervous system (CNS) has limited intrinsic regeneration capability. The study included patients with chronic complete SCI. Previously harvested autologous mesenchymal stem cells were administered at the site of injury after a laminectomy. Follow-up was done by a neutral examiner not involved in the surgery every 3 months. One patient had improvement in motor power. Two patients had a patchy improvement in pin prick sensation below the level of injury. Three different, progressively increasing doses did not result in improvement in the clinical outcome. Though the administration of allogenic human mesenchymal stem cells is safe in patients with SCI, it may not be efficacious; especially in patients with chronic SCI.

Adult stem cell therapies for neurological disorders: benefits beyond neuronal replacement?

The modest capacity of endogenous repair processes in the central nervous system (CNS) justifies the broad interest in the development of effective stem cell based therapies for neurodegenerative disorders and other acute or chronic lesions. Motivated by the ambitious expectation to achieve functional neuronal replacement, several studies have already evidenced a potential benefit of stem cell grafts in animal models of human disorders. Nevertheless, growing evidence suggests that the effects orchestrated by stem cells, in most experimental cases, are not necessarily associated with the generation of new neurons. This hypothesis correlates with the versatile properties of adult and embryonic stem cells. When introduced into the lesioned CNS, nondifferentiated stem cells can have a positive influence through intrinsic neuroprotective capacities related to the production of neurotrophic factors, stimulation of endogenous neurogenesis, and modulation of neuroinflammation. Stem cells are also endowed with a multipotent differentiation profile, suggesting that a positive outcome could result from the replacement of nonneuronal cell types, in particular astrocytes and oligodendrocytes. Focusing on adult stem cells, this Review aims at summarizing experimental observations supporting the concept that, in cell-based therapies, stem cells operate not through a unidirectional mechanism (e.g., generating neurons) but rather as cellular mediators of a multitude of biological activities that could provide a favorable outcome for diverse nervous disorders.

"Small stem cells" in adult tissues: very small embryonic-like stem cells stand up!

This review summarizes information regarding the rare population of very small embryonic-like stem cells (VSELs) that has been identified in adult tissues, emphasizing both their unique morphological features and potential biological significance. We focus on their pluripotent nature and expression of markers characteristic for embryonic stem cells (ESCs), epiblast (EP)SCs, and primordial germ cells (PGCs). Furthermore, we will discuss their rank in the developmental hierarchy of the SC compartment as well as their relationship to other bone marrow-derived, primitive, nonhematopoietic SCs including: (i) endothelial progenitor cells (EPCs); (ii) mesenchymal (M)SCs; (iii) multipotent adult progenitor cells (MAPCs); (iv) marrow-isolated adult multilineage inducible (MIAMIs) cells; (v) multipotent adult (MA)SCs; and (vi) OmniCytes. We will also present different populations of very "small SCs" that have been recently described in the literature (e.g., spore-like cells and Lin(-)/ALDH(high) long-term repopulating hematopoietic SCs).

Bone marrow-derived cells expressing Iba1 are constitutively present as resident tissue macrophages in the mouse cochlea

Immune-mediated inner ear disorder has been well established as a clinical entity; however, the innate immune system of the inner ear is a poorly understood area of research with high clinical and immunological importance. Although the presence of resident tissue macrophages in the inner ear has been suggested, there has been some controversy. In this study, we analyzed the origin of cochlear resident macrophages and the contribution of hematopoietic bone marrow (BM) to the recruitment of macrophages in the cochlea. To visualize the localization of BM-derived cells, BM chimeric mice were made by transplantation of hematopoietic stem cells, which were genetically labeled with enhanced green fluorescent protein, into lethally irradiated C57BL/6 mice. The distribution and characteristics of BM-derived cells in the mouse cochlea were studied immunohistochemically. We successfully identified the constitutive presence of tissue resident macrophages in the spiral ligament and spiral ganglion that are derived from BM in larger numbers than previously reported. Moreover, cochlear resident macrophages gradually turn over for several months during steady-state replacement by BM-derived cells, and the number of cochlear macrophages immediately increased in response to local surgical stress. The present findings demonstrate the hematopoietic origin of cochlear resident and infiltrating macrophages. Our study provides a novel anatomical and immunological basis for the inner ear and indicates that the cochlear resident macrophages would be a therapeutic target in inner ear disorders.

Amelioration of streptozotocin-induced diabetes in mice with cells derived from human marrow stromal cells

Background

Pluri-potent bone marrow stromal cells (MSCs) provide an attractive opportunity to generate unlimited glucose-responsive insulin-producing cells for the treatment of diabetes. We explored the potential for human MSCs (hMSCs) to be differentiated into glucose-responsive cells through a non-viral genetic reprogramming approach.

Methods and Findings

Two hMSC lines were transfected with three genes: PDX-1, NeuroD1 and Ngn3 without subsequent selection, followed by differentiation induction in vitro and transplantation into diabetic mice. Human MSCs expressed mRNAs of the archetypal stem cell markers: Sox2, Oct4, Nanog and CD34, and the endocrine cell markers: PDX-1, NeuroD1, Ngn3, and Nkx6.1. Following gene transfection and differentiation induction, hMSCs expressed insulin in vitro, but were not glucose regulated. After transplantation, hMSCs differentiated further and ∼12.5% of the grafted cells expressed insulin. The graft bearing kidneys contained mRNA of insulin and other key genes required for the functions of beta cells. Mice transplanted with manipulated hMSCs showed reduced blood glucose levels (from 18.9+/−0.75 to 7.63+/−1.63 mM). 13 of the 16 mice became normoglycaemic (6.9+/−0.64 mM), despite the failure to detect the expression of SUR1, a K⁺-ATP channel component required for regulation of insulin secretion.

Conclusions

Our data confirm that hMSCs can be induced to express insulin sufficient to reduce blood glucose in a diabetic mouse model. Our triple gene approach has created cells that seem less glucose responsive in vitro but which become more efficient after transplantation. The maturation process requires further study, particularly the in vivo factors influencing the differentiation, in order to scale up for clinical purposes.

Very small embryonic-like (VSEL) stem cells in adult organs and their potential role in rejuvenation of tissues and longevity

Recently, we purified rare CXC chemokine receptor 4 expressing (CXCR4(+)) small stem cells (SCs) from the murine bone marrow (BM) that express markers characteristic for embryonic (E)SCs, epiblast (EP)SCs, and primordial germ cells (PGCs). We named these primitive cells very small embryonic-like (VSEL) SCs (VSELs). Our data indicate that VSELs are also present in many other organs in mice and that they may differentiate into cells from all three germ layers. Similar SCs were also isolated from human cord blood (CB) and mobilized peripheral blood (mPB). We hypothesize that VSELs are deposited during gastrulation and organogenesis in developing organs/tissues of mammals as a population of pluripotent stem cells (PSCs) that give rise to tissue committed monopotent SCs and that their number decreases with age. Therefore VSELs could play a pivotal role in normal rejuvenation of adult tissues as well as involvement in regeneration of damaged organs. Thus, these cells are potential SCs candidates for regenerative medicine and we envision that the regenerative potential of these cells could be harnessed to decelerate the aging processes.

Bone Marrow - Home of Versatile Stem Cells

SUMMARY: Bone marrow (BM) has been for many years primarily envisioned as the 'home organ' of hematopoietic stem cells (HSC). In this review we will discuss current views of the BM stem cell compartment and present data showing that BM in addition to HSC also contains a heterogeneous population of non-hematopoietic stem cells. These cells have been variously described in the literature as i) endothelial progenitor cells (EPC), ii) mes-enchymal stem cells (MSC), iii) multipotent adult progenitor cells (MAPC), iv) marrow-isolated adult multilineage inducible (MIAMI) cells, v) multipotent adult stem cells (MACS) and vi) very small embryonic-like (VSEL) stem cells. It is likely that in many cases similar or overlapping populations of primitive stem cells in the BM were detected using different experimental strategies and hence were assigned different names.

Very small embryonic-like (VSEL) stem cells: purification from adult organs, characterization, and biological significance

In this review, we discuss current views of the bone marrow (BM) stem cell (SC) compartment and present data showing that BM contains heterogeneous populations of hematopoietic (H)SCs and non-HSCs. These cells are variously described in the literature as: endothelial progenitor cells (EPCs); mesenchymal (M)SCs; multipotent adult progenitor cells (MAPCs); marrow-isolated adult multilineage inducible (MIAMI) cells; and multipotent adult (MA)SCs. In some cases, it is likely that similar or overlapping populations of primitive SCs in the BM detected using various experimental strategies were assigned different names. Recently, we purified rare CXC chemokine receptor 4 expressing (CXCR4(+)) small SCs from the murine BM that express markers characteristic for embryonic (E)SCs, epiblast (EP)SCs, and primordial germ cells (PGCs). We named these primitive cells very small embryonic-like (VSEL) SCs. Our data indicate that VSELs may differentiate into cells from all three germ layers.

Transplantation of human bone marrow-derived stromal cells into the contused spinal cord of nude rats

OBJECT

Human bone marrow stromal cells (hMSCs) constitute a potential source of pluripotent stem cells. In the present study, hMSCs were transplanted into an area of spinal cord contusion in nude rats to determine their survival, differentiation, potential for neuroprotection, and influence on axonal growth and functional recovery.

METHODS

Twenty-nine animals received 6 x 10(5) hMSCs in 6 microl medium 1 week after a contusion, while 14 control animals received an injection of 6 microl medium alone. Basso-Beattie-Bresnahan (BBB) tests were performed weekly. The spinal cords were collected at 6 weeks posttransplantation for histological analysis and assessment of tissue injury.

RESULTS

Immunostaining with anti-human mitochondria antibody and pretransplantation labeling with green fluorescent protein demonstrated that the grafted hMSCs survived and were capable of achieving a flattened appearance in the grafted area; however, none of the transplanted cells stained positively for human-specific neuronal, anti-neurofilament H or glial fibrillary acidic protein within the sites of engraftment. While neuronal or astrocytic differentiation was not seen, cells lining blood vessels in the vicinity of the transplant stained positively for anti-human endothelium CD105 antibody. Staining for anti-neurofilament H antibody demonstrated abundant axonlike structures around the transplanted area in the hMSC group. Tissue sparing analysis showed that animals with grafted hMSCs had a smaller area of contusion cyst compared with controls, but there was no significant difference between the two groups in BBB scores.

CONCLUSIONS

The grafted hMSCs survived for > or = 6 weeks posttransplantation, although they did not differentiate into neural or glial cells. Cells with human endothelial characteristics were observed. Spinal cord-injured rats grafted with hMSCs had smaller contusion cavities, which did not have a significant influence on functional recovery.

Hunt for pluripotent stem cell -- regenerative medicine search for almighty cell

Regenerative medicine and tissue engineering are searching for a novel stem cell based therapeutic strategy that will allow for efficient treatment or even potential replacement of damaged organs. The pluripotent stem cell (PSC), which gives rise to cells from all three germ lineages, seems to be the most ideal candidate for such therapies. PSC could be extracted from developing embryos. However, since this source of stem cells for potential therapeutic purposes remains controversial, stem cell researchers look for PSC that could be isolated from the adult tissues or generated from already differentiated cells. True PSC should possess both potential for multilineage differentiation in vitro and, more importantly, also be able to complement in vivo blastocyst development. This review will summarize current approaches and limitations to isolate PSC from adult tissues or, alternatively, to generate it by nuclear reprogramming from already differentiated somatic cells.

Bone-marrow-derived stem cells--our key to longevity?

Bone marrow (BM) was for many years primarily regarded as the source of hematopoietic stem cells. In this review we discuss current views of the BM stem cell compartment and present data showing that BM contains not only hematopoietic but also heterogeneous non-hematopoietic stem cells. It is likely that similar or overlapping populations of primitive non-hematopoietic stem cells in BM were detected by different investigators using different experimental strategies and hence were assigned different names (e.g., mesenchymal stem cells, multipotent adult progenitor cells, or marrow-isolated adult multilineage inducible cells). However, the search still continues for true pluripotent stem cells in adult BM, which would fulfill the required criteria (e.g. complementation of blastocyst development). Recently our group has identified in BM a population of very small embryonic-like stem cells (VSELs), which express several markers characteristic for pluripotent stem cells and are found during early embryogenesis in the epiblast of the cylinder-stage embryo.

Formation of neurons by non-neural adult stem cells: potential mechanism implicates an artifact of growth in culture

Trans-differentiation is a mechanism proposed to explain how tissue-specific stem cells could generate cells of other organs, thus supporting the emerging concept of enhanced adult stem cell plasticity. Although spontaneous cell fusion rather than trans-differentiation may explain some unexpected cell fate changes in vivo, such a mechanism does not explain potential trans-differentiation events in vitro, including the generation of neural cell types from cultured bone marrow-derived stem cells. Here we present evidence that shows that cultured bone marrow-derived stem cells express neural proteins and form structures resembling neurons under defined growth conditions. We demonstrate that these changes in cell structure and neural protein expression are not consistent with typical neural development. Furthermore, the ability of bone marrow-derived stem cells to adopt a neural phenotype in vitro may occur as a result of cellular stress in response to removing cells from their niche and their growth in alternative environmental conditions. These findings suggest a potential explanation for the growth behavior of cultured bone marrow-derived stem cells and highlight the need to carefully validate the plasticity of stem cell differentiation.

Primitive and committed human hematopoietic progenitor cells interact with primary murine neural cells and are induced to undergo self-renewing cell divisions

OBJECTIVE

Studies in animal models have indicated that hematopoietic progenitor cells (HPC) migrate and home to the central nervous system and might acquire neural features under specific circumstances. The interaction between HPC and the neural environment and the functional effect on hematopoiesis have not yet been defined.

METHODS

CD34(+)133(+) cells from mobilized peripheral blood were cocultured with primary murine neurons or astrocytes. Chemotaxis and adhesive interactions were studied by applying beta(1)- and beta(2)-integrin function-blocking anibodies. The impact of neural feeder layers on integrin expression of HPC and the presence of appropriate adhesion ligands on neural cells were determined by immunostaining and flow cytometry. The hematopoietic long-term fate was monitored by time-lapse microscopy of individual cell-division history followed by long-term culture-initiating cell (LTC-IC) and colony-forming cell (CFC) assays. Neural differentiation was assessed by immunostaining against specific neuronal and glial antigens.

RESULTS

The 23.0% +/- 4.9% of HPC showed stromal cell-derived factor-1-induced migration toward neural cells, and 20.2% +/- 1.6% displayed firm beta(1)-integrin-mediated adhesion to astrocytes. The latter expressed appropriate adhesion ligands, stabilized beta(1)-integrin expression, and increased beta(2)-integrin expression of HPC. Neural differentiation of HPC could not be identified but astrocytes were able to induce limited self-renewing cell divisions of HPC and thus maintain 25.8% +/- 3.4% of the initial LTC-IC and 80.7% +/- 1.9% of the initial CFC.

CONCLUSION

Human HPC are able to interact with neural cells and interaction maintains, albeit to a limited extent, the self-renewal capability of HPC.

The Use of Stem Cells’ Hematopoietic Stimulating Factors Therapy Following Spinal Cord Injury

Spinal cord injury (SCI) remains one of the most devastating conditions in medicine, particularly due to the loss of productive life years and the high economic burden it places on our society. There are limited therapeutic options available to reduce the morbidity and mortality related to SCI. However, recent work with stem cells in repairing SCI appears to be promising, making this one of the most exciting frontiers in medicine. A brief review of the mechanisms of SCI is presented. Stem cells from a variety of sources have shown effectiveness in improving motor function after SCI in animals. The pre-clinical use of stem cells in SCI and methods of delivery are discussed. The potential use of granulocyte-colony stimulating factor (G-CSF) to increase the number of stem cells engrafting at the site of injury in order to improve neurological and motor function recovery following SCI is introduced. G-CSF, through stimulation of lymphohemopoietic stem cells in peripheral blood, can potentially cause repopulation of the SCI region with neural progenitor cells. This allows for improved functional outcomes. More pre-clinical and translational research exploring this possibility is required.

Revisiting the astrocyte–oligodendrocyte relationship in the adult CNS

The lineages of both astrocytes and oligodendrocytes have been popular areas of research in the last decade. The source of these cells in the mature CNS is relevant to the study of the cellular response to CNS injury. A significant amount of evidence exists to suggest that resident precursor cells proliferate and differentiate into mature glial cells that facilitate tissue repair and recovery. Additionally, the re-entry of mature astrocytes into the cell cycle can also contribute to the pool of new astrocytes that are observed following CNS injury. In order to better understand the glial response to injury in the adult CNS we must revisit the astrocyte-oligodendrocyte relationship. Specifically, we argue that there is a common glial precursor cell from which astrocytes and oligodendrocytes differentiate and that the microenvironment surrounding the injury determines the fate of the stimulated precursor cell. Ideally, better understanding the origin of new glial cells in the injured CNS will facilitate the development of therapeutics targeted to alter the glial response in a beneficial way.

Neurotrophin-3 administration alters neurotrophin, neurotrophin receptor and nestin mRNA expression in rat dorsal root ganglia following axotomy

In the months following transection of adult rat peripheral nerve some sensory neurons undergo apoptosis. Two weeks after sciatic nerve transection some neurons in the L4 and L5 dorsal root ganglia begin to show immunoreactivity for nestin, a filament protein expressed by neuronal precursors and immature neurons, which is stimulated by neurotrophin-3 (NT-3) administration. The aim of this study was to examine whether NT-3 administration could be compensating for decreased production of neurotrophins or their receptors after axotomy, and to determine the effect on nestin synthesis. The levels of mRNA in the ipsilateral and contralateral L4 and L5 dorsal root ganglia were analyzed using real-time polymerase chain reaction, 1 day, 1, 2 and 4 weeks after unilateral sciatic nerve transection and NT-3 or vehicle administration via s.c. micro-osmotic pumps. In situ hybridization was used to identify which cells and neurons expressed mRNAs of interest, and the expression of full-length trkC and p75NTR protein was investigated using immunohistochemistry. Systemic NT-3 treatment increased the expression of brain-derived neurotrophic factor, nestin, trkA, trkB and trkC mRNA in ipsilateral ganglia compared with vehicle-treated animals. Some satellite cells surrounding neurons expressed trkA and trkC mRNA and trkC immunoreactivity. NT-3 administration did not affect neurotrophin mRNA levels in the contralateral ganglia, but decreased the expression of trkA mRNA and increased the expression of trkB mRNA and p75NTR mRNA and protein. These data suggest that systemically administered NT-3 may counteract the decrease, or even increase, neurotrophin responsiveness in both ipsi- and contralateral ganglia after nerve injury.

Granulocyte colony-stimulating factor (G-CSF) mobilizes bone marrow-derived cells into injured spinal cord and promotes functional recovery after compression-induced spinal cord injury in mice

The aim of the present study was to elucidate the effects of granulocyte colony-stimulating factor (G-CSF)-mediated mobilization of bone marrow-derived stem cells on the injured spinal cord. Bone marrow cells of green fluorescent protein (GFP) transgenic mice were transplanted into lethally irradiated C57BL/6 mice. Four weeks after bone marrow transplantation, spinal cord injury was produced by a static load (20 g, 5 min) at T8 level. G-CSF (200 microg/kg/day) was injected subcutaneously for 5 days. Immunohistochemistry for GFP and cell lineage markers was performed to evaluate G-CSF-mediated mobilization of bone marrow-derived cells into injured spinal cord. Hind limb locomotor recovery was assessed for 6 weeks. Immunohistochemistry revealed that G-CSF increased the number of GFP-positive cells in injured spinal cord, indicating that bone marrow-derived cells were mobilized and migrated into injured spinal cord. The numbers of double positive cells for GFP and glial markers were larger in the G-CSF treated mice than in the control mice. Luxol Fast Blue staining revealed that G-CSF promoted white matter sparing. G-CSF treated mice showed significant recovery of hind limb function compared to that of the control mice. In conclusion, G-CSF showed efficacy for spinal cord injury treatment through mobilization of bone marrow-derived cells.

Bone marrow-derived very small embryonic-like stem cells: Their developmental origin and biological significance

Data from our and other laboratories provide evidence that bone marrow (BM) contains a population of stem cells that expresses early developmental markers such as (1) stage-specific embryonic antigen (SSEA) and (2) transcription factors Oct-4 and Nanog. These are the markers characteristic for embryonic stem cells, epiblast stem cells, and primordial germ cells (PGC). The presence of these stem cells in adult BM supports the concept that this organ contains some population of pluripotent stem cells that is deposited in embryogenesis during early gastrulation. We hypothesize that these cells could be direct descendants of the germ lineage that, to pass genes on to the next generations, has to create soma and, thus, becomes a "mother lineage" for all somatic cell lineages present in the adult body. Germ potential is established after conception in totipotent zygotes and retained in blastomeres of morula, cells from the inner cell mass of blastocyst, epiblast, and population of PGC. We will present a concept that SSEA(+) Oct-4(+) Nanog(+) cells identified in BM could be descendants of epiblast cells as well as some rare migrating astray PGC.

Differential effects of Th1, monocyte/macrophage and Th2 cytokine mixtures on early gene expression for immune-related molecules by central nervous system mixed glial cell cultures

Cytokines secreted within the central nervous system (CNS) are important in the development of multiple sclerosis (MS) lesions. The balance between Th1, monocyte/macrophage (M/M) and Th2 cytokines in the CNS may be pivotal in determining the outcome of lesion development. We examined the effects of mixtures of cytokines on gene expression by CNS glial cells, as mixtures of cytokines are present in MS lesions, which in turn contain mixtures of glial cells. In this initial analysis by gene array, we examined changes at 6 hours to identify early changes in gene expression that represent primary responses to the cytokines. Rat glial cells were incubated with mixtures of Th1, M/M and Th2 cytokines for 6 hours and examined for changes in early gene expression employing microarray gene chip technology. A minimum of 814 genes were differentially regulated by one or more of the cytokine mixtures in comparison to controls, including changes in expression in a large number of genes for immune system-related proteins. Expression of the proteins for these genes likely influences development and inhibition of MS lesions as well as protective and regenerative processes. Analysing gene expression for the effects of various combinations of exogenous cytokines on glial cells in the absence of the confounding effects of inflammatory cells themselves should increase our understanding of cytokine-induced pathways in the CNS.

Expression of 2',3'-cyclic nucleotide 3'-phosphodiesterase in the amoeboid microglial cells in the developing rat brain

Expression of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) in amoeboid microglial cells (AMC) in developing rat brain from prenatal day 18 (E18) to postnatal day 10 (P10) was demonstrated by immunohistochemistry/immunofluorescence and immunoelectron microscopy both in vivo and in vitro, respectively. Furthermore, real time-polymerase chain reaction (PCR) was performed to determine the expression of CNPase at mRNA level in cultured microglial cells in control conditions and following lipopolysaccharide stimulation. CNPase immunoreactive amoeboid microglia occurred in large numbers in the corpus callosum, subventricular zone and cavum septum pellucidum at P0 but were progressively reduced with age and were undetectable at P14. By immunoelectron microscopy, immunoreaction product was associated primarily with the plasma membrane, filopodial projections and mitochondria in AMC. Real time-PCR analysis revealed that CNPase mRNA was expressed by cultured amoeboid microglia and was significantly up-regulated in microglial activation induced in vitro by lipopolysaccharide. The functional role of CNPase in AMC remains speculative. Given its expression in AMC transiently occurring in the perinatal brain and that it is markedly elevated in activated microglia, it is suggested that the enzyme may be linked to the major functions of the cell type such as release of chemokines and cytokines. In relation to this, CNPase may play a key role associated with transportation of cytoplasmic materials.

Selective migration and engraftment of bone marrow mesenchymal stem cells in rat lumbar dorsal root ganglia after sciatic nerve constriction

Bone marrow mesenchymal stem cells (MSCs) preferentially migrate to the injured hemisphere when administered intravenously to rats with traumatic or ischemic brain injuries. In this study, we have investigated the localization of MSCs injected into the lumbar-4 dorsal root ganglion (L4-DRG) of rats with a sciatic nerve single ligature nerve constriction (SLNC). MSCs were isolated by their adherence to plastic, cultured until confluence and labelled with Hoechst. Animals with a unilateral injection of MSCs were subjected to an ipsilateral, bilateral or contralateral SLNC. After 9 days, they were perfused and the lumbar DRGs were dissected out, cut in a cryostat and observed with a fluorescence microscope. Large numbers of Hoechst-positive cells were observed in the injected L4-DRG, distributed around primary afferent neurons, resembling the anatomical localization of glial cells. In animals with an ipsilateral SLNC, some cells were detected in the ipsilateral L3, L5 or L6-DRGs but not in the contralateral ganglia. In animals with a bilateral lesion, MSCs migrated to both the ipsilateral and contralateral DRGs whereas in animals with a contralateral ligature, MSCs migrated to the contralateral DRGs. These results suggest that MSCs preferentially engraft in DRGs hosting primary sensory neurons affected by a lesion of their peripheral branches. Further studies should be carried out in order to elucidate the molecular mechanisms involved in this migration and homing, in order to evaluate the possible use of MSCs as a new therapeutic strategy for the treatment of peripheral nerve neuropathies.

Functional considerations of stem cell transplantation therapy for spinal cord repair

Stem cells hold great promise for therapeutic repair after spinal cord injury (SCI). This review compares the current experimental approaches taken towards a stem cell-based therapy for SCI. It critically evaluates stem cell sources, injury paradigms, and functional measurements applied to detect behavioral changes after transplantation into the spinal cord. Many of the documented improvements do not exclusively depend on lineage-specific cellular differentiation. In most of the studies, the functional tests used cannot unequivocally demonstrate how differentiation of the transplanted cells contributes to the observed effects. Standardized cell isolation and transplantation protocols could facilitate the assessment of the true contribution of various experimental parameters on recovery. We conclude that at present embryonic stem (ES)-derived cells hold the most promise for therapeutic utility, but that non-neural cells may ultimately be optimal if the mechanism of possible transdifferentiation can be elucidated.

Neuroprotective properties of the innate immune system and bone marrow stem cells in Alzheimer's disease

The role of innate immunity and microglia in the brain is currently a matter of great debate and controversy. While several studies have provided evidence that they contribute to neurodegeneration in various animal models of brain diseases and traumas, others have shown that their inhibition may in contrast be associated with more damages or less repair. We have recently reported the existence of two different types of microglia, the resident and the newly differentiated microglia that derive from the bone marrow stem cells. Of great interest is the fact that blood-derived microglial cells are associated with amyloid plaques and these cells are able to prevent the formation or eliminate the presence of amyloid deposits in mice that develop the major hallmark of Alzheimer's disease (AD). These newly recruited cells are specifically attracted to the beta-amyloid 40/42 isoforms in vivo and they participate in the elimination of these proteins by phagocytosis. This review presents the mechanisms involved in the control of the innate immune response by microglia and the beneficial properties of such a response in brain diseases, such as AD.

Angiogenic recruitment of pericytes from bone marrow after stroke

Bone marrow-derived cells (BMDCs) contribute to revascularization after ischemia. However, the mechanisms by which BMDCs support vessel remodeling after cerebral ischemia are not clear. Using mouse chimeras that express enhanced green fluorescent protein in reconstituted bone marrow, we investigated the role of BMDCs in revascularization and brain repair after middle cerebral artery occlusion of murine brain. After ischemia, two populations of BMDCs were observed, one in the brain parenchyma and another associated with the vasculature. The number of BMDCs that infiltrated the brain parenchyma peaked at 7 days and persisted through 14 days, the last time point observed. The majority of BMDCs were characterized as microglia, based on cell-type-specific marker expression. We observed a robust angiogenic response after cerebral ischemia. Bone marrow-derived cells associated with remodeling blood vessels were negative for endothelial markers, but were surrounded by basal lamina and expressed desmin and vimentin, identifying these cells as pericytes. Quantification of BMDCs that expressed desmin revealed increasing desmin expression with time. Perivascular associated BMDCs that expressed desmin were immunoreactive for the angiogenic factors vascular endothelial growth factor and transforming growth factor-beta. These findings suggest that pericytes are recruited from the periphery and are involved in blood vessel stabilization during ischemia-induced angiogenesis.