The therapeutic use of stem cells for myelin repair in autoimmune demyelinating disorders

Disease Modifying Strategies in Multiple Sclerosis: New Rays of Hope to Combat Disability?

Multiple sclerosis (MS) is the most prevalent chronic autoimmune inflammatory- demyelinating disorder of the central nervous system (CNS). It usually begins in young adulthood, mainly between the second and fourth decades of life. Usually, the clinical course is characterized by the involvement of multiple CNS functional systems and by different, often overlapping phenotypes. In the last decades, remarkable results have been achieved in the treatment of MS, particularly in the relapsing- remitting (RRMS) form, thus improving the long-term outcome for many patients. As deeper knowledge of MS pathogenesis and respective molecular targets keeps growing, nowadays, several lines of disease-modifying treatments (DMT) are available, an impressive change compared to the relative poverty of options available in the past. Current MS management by DMTs is aimed at reducing relapse frequency, ameliorating symptoms, and preventing clinical disability and progression. Notwithstanding the relevant increase in pharmacological options for the management of RRMS, research is now increasingly pointing to identify new molecules with high efficacy, particularly in progressive forms. Hence, future efforts should be concentrated on achieving a more extensive, if not exhaustive, understanding of the pathogenetic mechanisms underlying this phase of the disease in order to characterize novel molecules for therapeutic intervention. The purpose of this review is to provide a compact overview of the numerous currently approved treatments and future innovative approaches, including neuroprotective treatments as anti-LINGO-1 monoclonal antibody and cell therapies, for effective and safe management of MS, potentially leading to a cure for this disease.

An overall view of the most common experimental models for multiple sclerosis

Multiple sclerosis (MS) is a complex chronic disease with an unknown etiology. It is considered an inflammatory demyelinating and neurodegenerative disorder of the central nervous system (CNS) characterized, in most cases, by an unpredictable onset of relapse and remission phases. The disease generally starts in subjects under 40; it has a higher incidence in women and is described as a multifactorial disorder due to the interaction between genetic and environmental risk factors. Unfortunately, there is currently no definitive cure for MS. Still, therapies can modify the disease's natural history, reducing the relapse rate and slowing the progression of the disease or managing symptoms. The limited access to human CNS tissue slows down. It limits the progression of research on MS. This limit has been partially overcome over the years by developing various experimental models to study this disease. Animal models of autoimmune demyelination, such as experimental autoimmune encephalomyelitis (EAE) and viral and toxin or transgenic MS models, represent the most significant part of MS research approaches. These models have now been complemented by ex vivo studies, using organotypic brain slice cultures and in vitro, through induced Pluripotent Stem cells (iPSCs). We will discuss which clinical features of the disorders might be reproduced and investigated in vivo, ex vivo, and in vitro in models commonly used in MS research to understand the processes behind the neuropathological events occurring in the CNS of MS patients. The primary purpose of this review is to give the reader a global view of the main paradigms used in MS research, spacing from the classical animal models to transgenic mice and 2D and 3D cultures.

Selective killing of spinal cord neural stem cells impairs locomotor recovery in a mouse model of spinal cord injury

Background

Spinal cord injury (SCI) is a devastating condition mainly deriving from a traumatic damage of the spinal cord (SC). Immune cells and endogenous SC-neural stem cells (SC-NSCs) play a critical role in wound healing processes, although both are ineffective to completely restore tissue functioning. The role of SC-NSCs in SCI and, in particular, whether such cells can interplay with the immune response are poorly investigated issues, although mechanisms governing such interactions might open new avenues to develop novel therapeutic approaches.

Methods

We used two transgenic mouse lines to trace as well as to kill SC-NSCs in mice receiving SCI. We used Nestin CreERT2 mice to trace SC-NSCs descendants in the spinal cord of mice subjected to SCI. While mice carrying the suicide gene thymidine kinase (TK) along with the GFP reporter, under the control of the Nestin promoter regions (Nestin^TK mice) were used to label and selectively kill SC-NSCs.

Results

We found that SC-NSCs are capable to self-activate after SCI. In addition, a significant worsening of clinical and pathological features of SCI was observed in the Nestin^TK mice, upon selective ablation of SC-NSCs before the injury induction. Finally, mice lacking in SC-NSCs and receiving SCI displayed reduced levels of different neurotrophic factors in the SC and significantly higher number of M1-like myeloid cells.

Conclusion

Our data show that SC-NSCs undergo cell proliferation in response to traumatic spinal cord injury. Mice lacking SC-NSCs display overt microglia activation and exaggerate expression of pro-inflammatory cytokines. The absence of SC-NSCs impaired functional recovery as well as neuronal and oligodendrocyte cell survival. Collectively our data indicate that SC-NSCs can interact with microglia/macrophages modulating their activation/responses and that such interaction is importantly involved in mechanisms leading tissue recovery.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1085-9) contains supplementary material, which is available to authorized users.

Transdifferentiation of Human Dental Pulp Stem Cells Into Oligoprogenitor Cells

Introduction

The nerve fibers in central nervous system are surrounded by myelin sheet which is formed by oligodendrocytes. Cell therapy based on oligodendrocytes and their precursors transplantation can hold a promising alternative treatment for myelin sheet repair in demyelinating diseases.

Methods

Human Dental Pulp Stem Cells (hDPSCs) are noninvasive, autologous and easy available source with multipotency characteristics, so they are in focus of interest in regenerative medicine. In the present study, hDPSCs were differentiated into oligoprogenitor using glial induction media, containing Retinoic Acid (RA), basic Fibroblast Growth Factor (bFGF), Platelet-Derived Growth Factor (PDGF), N2 and B27. The differentiated Oligoprogenitor Cells (OPCs) were evaluated for nestin, Olig2, NG2 and O4 using immunocytochemistry. Also, the expression of nestin, Olig2 and PDGFR-α gens (neuroprogenitor and oligoprogenitor markers) were investigated via RT-PCR technique.

Results

The results indicate that glial differentiation medium induces the generation of oligoprogenitor cells as revealed via exhibition of specific glial markers, including Olig2, NG2 and O4. The expersion of nestin gene (neuroprogenitor marker) and Olig2 and PDGFR-α genes (oligoprogentor markers) were detected in treated hDPSCs at the end of the induction stage.

Conclusion

hDPSCs can be induced to transdifferentiate into oligoprogenitor cells and respond to the routinely applied regents for glial differentiation of mesanchymal stem cells. These data suggest the hDPSCs as a valuable source for cell therapy in neurodegenerative diseases.

Placental Stromal Cell Therapy for Experimental Autoimmune Encephalomyelitis: The Role of Route of Cell Delivery

Multiple sclerosis (MS) is an immune‐mediated disease of the central nervous system (CNS) with no effective treatment available for the chronic‐progressive stage. Cell therapy is a promising therapeutic approach for attenuating the immune‐mediated CNS process. Isolated and expanded human placental stromal cells (hPSCs) possess potent immunomodulatory and trophic properties, making them a good candidate for MS therapy. We examined the potential of hPSC therapy in preventing the onset or attenuating the course of established disease in a murine MS model of myelin oligodendrocyte glycoprotein‐induced experimental autoimmune encephalomyelitis. We examined the feasibility of hPSC systemic delivery by intramuscular (i.m.) implantation rather than the commonly used intravenous injection, which is dose‐limiting and carries the risk of pulmonary obstruction. Our findings showed significant attenuation of the disease only when hPSCs were injected directly to the central nervous system. Intramuscular implanted hPSCs survived at the site of injection for at least 2 months and elicited extensive local immune responses. Intramuscular hPSC implantation before disease onset caused a delay in the appearance of clinical signs and reduced the severity of a relapse induced by repeated challenge with the autoantigen. Intramuscular implantation after disease onset did not affect its course. Thus, pathological analysis of CNS tissue did not show inhibition of neuroinflammation in i.m. hPSC‐implanted mice. Moreover, no apparent effect was seen on the proliferative response of peripheral lymph node cells in these animals. We conclude that to maximize their therapeutic potential in MS, hPSCs should be delivered directly to the affected CNS. Stem Cells Translational Medicine2017;6:1286–1294

Microenvironmental regulation of oligodendrocyte replacement and remyelination in spinal cord injury

Myelin is a proteolipid sheath enwrapping axons in the nervous system that facilitates signal transduction along the axons. In the central nervous system (CNS), oligodendrocytes are specialized glial cells responsible for myelin formation and maintenance. Following spinal cord injury (SCI), oligodendroglia cell death and myelin damage (demyelination) cause chronic axonal damage and irreparable loss of sensory and motor functions. Accumulating evidence shows that replacement of damaged oligodendrocytes and renewal of myelin (remyelination) are promising approaches to prevent axonal degeneration and restore function following SCI. Neural precursor cells (NPCs) and oligodendrocyte progenitor cells (OPCs) are two main resident cell populations in the spinal cord with innate capacities to foster endogenous oligodendrocyte replacement and remyelination. However, due to the hostile microenvironment of SCI, the regenerative capacity of these endogenous precursor cells is conspicuously restricted. Activated resident glia, along with infiltrating immune cells, are among the key modulators of secondary injury mechanisms that create a milieu impermissible to oligodendrocyte differentiation and remyelination. Recent studies have uncovered inhibitory roles for astrocyte-associated molecules such as matrix chondroitin sulfate proteoglycans (CSPGs), and a plethora of pro-inflammatory cytokines and neurotoxic factors produced by activated microglia/macrophages. The quality of axonal remyelination is additionally challenged by dysregulation of the supportive growth factors required for maturation of new oligodendrocytes and axo-oligodendrocyte signalling. Careful understanding of factors that modulate the activity of endogenous precursor cells in the injury microenvironment is a key step in developing efficient repair strategies for remyelination and functional recovery following SCI.

Integrin/Chemokine receptor interactions in the pathogenesis of experimental autoimmune encephalomyelitis

Excessive infiltration of leukocytes and the elaboration of inflammatory cytokines are believed to be responsible for the observed damage to neurons and oligodendrocytes during multiple sclerosis (MS). Blocking adhesion molecules or preventing the effects of chemotactic mediators such as chemokines can be exploited to prevent immune cell recruitment to inflamed tissues. An anti-α4 integrin antibody (anti-VLA-4mAb/natalizumab (Tysabri®)) has been used as a treatment for MS and reduces leukocyte influx into the brain. In patients, anti-VLA-4 reduces relapses and disability progression. However, its mechanism of action in the brain is not completely understood. The anti-VLA-4mAb was demonstrated to mobilize hematopoietic progenitor cells. Interestingly, the chemokine SDF-1/CXCL12 and its receptor CXCR4 are also key factors regulating the migration of hematopoietic stem cells. Moreover, studies have revealed a crosstalk between SDF-1/CXCR4 and VLA-4 signaling in regulating cell migration. In this study, we address the effects of anti-VLA-4 on chemokine signaling in the brain during MS. We assessed the ability of anti-VLA-4 to regulate Experimental Autoimmune Encephalomyelitis (EAE) and chemokine/receptor signaling. Preclinical administration of anti-VLA-4 delayed clinical signs of EAE. We found that anti-VLA-4 treatment reduced chemokine expression. In order to further explore the interaction of anti-VLA-4 with chemokine/receptor signaling we used dual color transgenic mice. After EAE induction, the expression of both SDF-1/CXCL12 and CXCR4 receptor was upregulated, treatment with anti-VLA-4 inhibited this effect. The effects of anti-VLA-4 on chemokine signaling in the CNS may be of importance when considering its mechanism of action and understanding the pathogenesis of EAE.

Stem cell-like dog placenta cells afford neuroprotection against ischemic stroke model via heat shock protein upregulation

In this study, we investigated the dog placenta as a viable source of stem cells for stroke therapy. Immunocytochemical evaluation of phenotypic markers of dog placenta cells (DPCs) cultured in proliferation and differentiation medium revealed that DPCs expressed both stem cell and neural cell markers, respectively. Co-culture with DPCs afforded neuroprotection of rat primary neural cells in a dose-dependent manner against oxygen-glucose deprivation. Subsequent in vivo experiments showed that transplantation of DPCs, in particular intravenous and intracerebral cell delivery, produced significant behavioral recovery and reduced histological deficits in ischemic stroke animals compared to those that received intra-arterial delivery of DPCs or control stroke animals. Furthermore, both in vitro and in vivo studies implicated elevated expression of heat shock protein 27 (Hsp27) as a potential mechanism of action underlying the observed therapeutic benefits of DPCs in stroke. This study supports the use of stem cells for stroke therapy and implicates a key role of Hsp27 signaling pathway in neuroprotection.

Overexpression of CD44 in neural precursor cells improves trans-endothelial migration and facilitates their invasion of perivascular tissues in vivo

Neural precursor (NPC) based therapies are used to restore neurons or oligodendrocytes and/or provide neuroprotection in a large variety of neurological diseases. In multiple sclerosis models, intravenously (i.v) -delivered NPCs reduced clinical signs via immunomodulation. We demonstrated recently that NPCs were able to cross cerebral endothelial cells in vitro and that the multifunctional signalling molecule, CD44 involved in trans-endothelial migration of lymphocytes to sites of inflammation, plays a crucial role in extravasation of syngeneic NPCs. In view of the role of CD44 in NPCs trans-endothelial migration in vitro, we questioned presently the benefit of CD44 overexpression by NPCs in vitro and in vivo, in EAE mice. We show that overexpression of CD44 by NPCs enhanced over 2 folds their trans-endothelial migration in vitro, without impinging on the proliferation or differentiation potential of the transduced cells. Moreover, CD44 overexpression by NPCs improved significantly their elongation, spreading and number of filopodia over the extracellular matrix protein laminin in vitro. We then tested the effect of CD44 overexpression after i.v. delivery in the tail vein of EAE mice. CD44 overexpression was functional invivo as it accelerated trans-endothelial migration and facilitated invasion of HA expressing perivascular sites. These in vitro and in vivo data suggest that CD44 may be crucial not only for NPC crossing the endothelial layer but also for facilitating invasion of extravascular tissues.

Olig1 function is required for remyelination potential of transplanted neural progenitor cells in a model of viral-induced demyelination

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) resulting in cumulative neurologic deficits associated with progressive myelin loss. We have previously shown that transplantation of neural progenitor cells (NPCs) into mice persistently infected with the JHM strain of mouse hepatitis virus (JHMV) results in enhanced differentiation into oligodendrocyte progenitor cells (OPCs) that is associated with remyelination and axonal sparing. The current study examines the contributions of the transcription factor Olig1 on NPC differentiation and remyelination. Under defined conditions, NPCs preferentially differentiate into oligodendroglia whereas NPCs isolated from Olig1-deficient (Olig1-/-) mice exhibit enhanced differentiation into astrocytes. Transplantation of Olig1-/- and Olig1+/+ NPCs into JHMV-infected mice resulted in similar cell survival, proliferation, and selective migration to areas of demyelination. However, only recipients of wild type NPCs exhibited extensive remyelination compared to mice receiving Olig1-/- NPCs. In vivo characterization of NPCs revealed that Olig1+/+ NPCs preferentially differentiated into NG2-positive OPCs and formed processes expressing myelin basic protein that encircled axons. In contrast, the majority of transplanted Olig1-/- NPCs differentiated into GFAP-positive cells consistent with the astrocyte lineage. These results indicate that exogenous NPCs contribute to improved clinical and histological outcome and this is associated with remyelination by this donor population. Further, these findings reveal that Olig1function is required for the remyelination potential of NPCs after transplant, through specification and/or maintenance of oligodendroglial identity.

Intravenous administration of human embryonic stem cell-derived neural precursor cells attenuates cuprizone-induced central nervous system (CNS) demyelination

AIMS

Previous studies have demonstrated the therapeutic potential for human embryonic stem cell-derived neural precursor cells (hES-NPCs) in autoimmune and genetic animal models of demyelinating diseases. Herein, we tested whether intravenous (i.v.) administration of hES-NPCs would impact central nervous system (CNS) demyelination in a cuprizone model of demyelination.

METHODS

C57Bl/6 mice were fed cuprizone (0.2%) for 2 weeks and then separated into two groups that either received an i.v. injection of hES-NPCs or i.v. administration of media without these cells. After an additional 2 weeks of dietary cuprizone treatment, CNS tissues were analysed for detection of transplanted cells and differences in myelination in the region of the corpus callosum (CC).

RESULTS

Cuprizone-induced demyelination in the CC was significantly reduced in mice treated with hES-NPCs compared with cuprizone-treated controls that did not receive stem cells. hES-NPCs were identified within the brain tissues of treated mice and revealed migration of transplanted cells into the CNS. A limited number of human cells were found to express the mature oligodendrocyte marker, O1, or the astrocyte marker, glial fibrillary acidic protein. Reduced apoptosis and attenuated microglial and astrocytic responses were also observed in the CC of hES-NPC-treated mice.

CONCLUSIONS

These findings indicated that systemically administered hES-NPCs migrated from circulation into a demyelinated lesion within the CNS and effectively reduced demyelination. Observed reductions in astrocyte and microglial responses, and the benefit of hES-NPC treatment in this model of myelin injury was not obviously accountable to tissue replacement by exogenously administered cells.

MicroRNAs: novel regulators of oligodendrocyte differentiation and potential therapeutic targets in demyelination-related diseases

MicroRNAs (miRNAs or miRs) are a class of endogenous small non-coding RNAs that consist of about 22 nucleotides and play critical roles in various biological processes, including cell proliferation, differentiation, apoptosis, and tumorigenesis. In recent years, some specific miRNA, such as miR-219, miR-138, miR-9, miR-23, and miR-19b were found to participate in the regulation of oligodendrocyte (OL) differentiation and myelin maintenance, as well as in the pathogenesis of demyelination-related diseases (e.g., multiple sclerosis, ischemic stroke, and leukodystrophy). These miRNAs control their target mRNA or regulate the protein levels of some signaling pathways, and participate in OL differentiation and the pathogenesis of demyelination-related diseases. During pathologic processes, the expression levels of specific miRNAs are dynamically altered. Therefore, miRNAs act as diagnostic and prognostic indicators of defects in OL differentiation and demyelination-related diseases, and they can provide potential targets for therapeutic drug development.

Magnetic iron oxide nanoparticles for biomedical applications

Due to their high magnetization, superparamagnetic iron oxide nanoparticles induce an important decrease in the transverse relaxation of water protons and are, therefore, very efficient negative MRI contrast agents. The knowledge and control of the chemical and physical characteristics of nanoparticles are of great importance. The choice of the synthesis method (microemulsions, sol-gel synthesis, laser pyrolysis, sonochemical synthesis or coprecipitation) determines the magnetic nanoparticle's size and shape, as well as its size distribution and surface chemistry. Nanoparticles can be used for numerous in vivo applications, such as MRI contrast enhancement and hyperthermia drug delivery. New developments focus on targeting through molecular imaging and cell tracking.

Oligodendrogenesis in the subventricular zone and the role of epidermal growth factor

Demyelinating diseases are characterized by an extensive loss of oligodendrocytes and myelin sheaths from axolemma. These neurological disorders are a common cause of disability in young adults, but so far, there is no effective treatment against them. It has been suggested that neural stem cells (NSCs) may play an important role in brain repair therapies. NSCs in the adult subventricular zone (SVZ), also known as Type-B cells, are multipotential cells that can self-renew and give rise to neurons and glia. Recent findings have shown that cells derived from SVZ Type-B cells actively respond to epidermal-growth-factor (EGF) stimulation becoming highly migratory and proliferative. Interestingly, a subpopulation of these EGF-activated cells expresses markers of oligodendrocyte precursor cells (OPCs). When EGF administration is removed, SVZ-derived OPCs differentiate into myelinating and pre-myelinating oligodendrocytes in the white matter tracts of corpus callosum, fimbria fornix and striatum. In the presence of a demyelinating lesion, OPCs derived from EGF-stimulated SVZ progenitors contribute to myelin repair. Given their high migratory potential and their ability to differentiate into myelin-forming cells, SVZ NSCs represent an important endogenous source of OPCs for preserving the oligodendrocyte population in the white matter and for the repair of demyelinating injuries.

The role of CXCR4 signaling in the migration of transplanted oligodendrocyte progenitors into the cerebral white matter

Enhancing the ability of either endogenous or transplanted oligodendrocyte progenitors (OPs) to engage in myelination may constitute a novel therapeutic approach to demyelinating diseases of the brain. It is known that in adults neural progenitors situated in the subventricular zone of the lateral ventricle (SVZ) are capable of generating OPs which can migrate into white matter tracts such as the corpus callosum (CC). We observed that progenitor cells in the SVZ of adult mice expressed CXCR4 chemokine receptors and that the chemokine SDF-1/CXCL12 was expressed in the CC. We therefore investigated the role of chemokine signaling in regulating the migration of OPs into the CC following their transplantation into the lateral ventricle. We established OP cell cultures from Olig2-EGFP mouse brains. These cells expressed a variety of chemokine receptors, including CXCR4 receptors. Olig2-EGFP OPs differentiated into CNPase-expressing oligodendrocytes in culture. To study the migratory capacity of Olig2-EGFP OPs in vivo, we transplanted them into the lateral ventricles of mice. Donor cells migrated into the CC and differentiated into mature oligodendrocytes. This migration was enhanced in animals with Experimental Autoimmune Encephalomyelitis (EAE). Inhibition of CXCR4 receptor expression in OPs using shRNA inhibited the migration of transplanted OPs into the white matter suggesting that their directed migration is regulated by CXCR4 signaling. These findings indicate that CXCR4 mediated signaling is important in guiding the migration of transplanted OPs in the context of inflammatory demyelinating brain disease.

Cross-talk between CD4+ T-cells and neural stem/progenitor cells

Immune-neural interactions dictate both lesion formation and repair in multiple sclerosis (MS). MS pathogenesis is mediated by the interplay of invading immune cells, neurons, glia, and endogenous stores of neural stem/progenitor cells (NPCs). However, the signals important in this cross-talk are not well defined. We utilized a co-culture method and flow cytometric analysis capable of detecting outcomes for both cell types. Here we describe the effects of NPCs on three different CD4+ subtypes (Th1, Th2, and Th17) and vice versa. Utilizing lpr (Fas receptor-deficient) and gld (Fas ligand-deficient) NPC lines, we further define the role of Fas in this neuroimmune cross-talk. We show that only the Th1 subtype is capable of inducing NPC cell death, and this is independent of Fas activation. Conversely, NPCs specifically kill pro-inflammatory Th1 and Th17 cells in a contact-dependent manner without affecting Th2 survival. Further investigation into these effects revealed that FasL expressed by NPCs mediates Th17 apoptosis. Additionally NPC/T-cell cross-talk modulates FasL expression in both cell types, while Fas receptor levels remains static. These findings illuminate the direct neuropathogenic effects of T-cells, as well as help define the immunomodulatory capacity of NPCs. We have elucidated novel interactions that may be critical in MS pathogenesis.

Variable behavior and complications of autologous bone marrow mesenchymal stem cells transplanted in experimental autoimmune encephalomyelitis

Autologous bone marrow stromal cells (BMSCs) offer significant practical advantages for potential clinical applications in multiple sclerosis (MS). Based on recent experimental data, a number of clinical trials have been designed for the intravenous (IV) and/or intrathecal (ITH) administration of BMSCs in MS patients. Delivery of BMSCs in the cerebrospinal fluid via intracerebroventricular (ICV) transplantation is a useful tool to identify mechanisms underlying the migration and function of these cells. In the current study, BMSCs were ICV administered in severe and mild EAE, as well as naive animals; neural precursor cells (NPCs) served as cellular controls. Our data indicated that ICV-transplanted BMSCs significantly ameliorated mild though not severe EAE. Moreover, BMSCs exerted significant anti-inflammatory effect on spinal cord with concomitant reduced axonopathy only in the mild EAE model. BMSCs migrated into the brain parenchyma and, depending on their cellular density, within brain parenchyma formed cellular masses characterized by focal inflammation, demyelination, axonal loss and increased collagen-fibronectin deposition. These masses were present in 64% of ICV BMASC-transplanted severe EAE animals whereas neither BMSCs transplanted in mild EAE cases nor the NPCs exhibited similar behavior. BMSCs possibly exerted their fibrogenic effect via both paracrine and autocrine manner, at least partly due to up-regulation of connective tissue growth factor (CTGF) under the trigger of TGFb1. Our findings are of substantial relevance for clinical trials in MS, particularly regarding the possibility that ICV transplanted BMSCs entering the inflamed central nervous system may exhibit - under conditions - a local pathology of yet unknown consequences.

New developments in the treatment of optic neuritis

Acute optic neuritis (ON) has various etiologies. The most common presentation is inflammatory, demyelinating, idiopathic, or "typical" ON, which may be associated with multiple sclerosis. This must be differentiated from "atypical" causes of ON, which differ in their clinical presentation, natural history, management, and prognosis. Clinical "red flags" for an atypical cause of ON include absent or persistent pain, exudates and hemorrhages on fundoscopy, very severe, bilateral, or progressive visual loss, and failure to recover. In typical ON, steroids shorten the duration of the attack, but do not influence visual outcome. This is in contrast to atypical ON associated with conditions such as sarcoidosis and neuromyelitis optica, which require aggressive immunosuppression and sometimes plasma exchange. The visual prognosis of typical ON is generally good. The prognosis in atypical ON is more variable. New developments aimed at designing better treatments for patients who fail to recover are discussed, focusing on recent research elucidating mechanisms of damage and recovery in ON. Future therapeutic directions may include enhancing repair processes, such as remyelination or adaptive neuroplasticity, or alternative methods of immunomodulation. Pilot studies investigating the safety and proof-of-principle of stem cell treatment are currently underway.

Epidermal growth factor induces the progeny of subventricular zone type B cells to migrate and differentiate into oligodendrocytes

New neurons and oligodendrocytes are continuously produced in the subventricular zone (SVZ) of adult mammalian brains. Under normal conditions, the SVZ primary precursors (type B1 cells) generate type C cells, most of which differentiate into neurons, with a small subpopulation giving rise to oligodendrocytes. Epidermal growth factor (EGF) signaling induces dramatic proliferation and migration of SVZ progenitors, a process that could have therapeutic applications. However, the fate of cells derived from adult neural stem cells after EGF stimulation remains unknown. Here, we specifically labeled SVZ B1 cells and followed their progeny after a 7-day intraventricular infusion of EGF. Cells derived from SVZ B1 cells invaded the parenchyma around the SVZ into the striatum, septum, corpus callosum, and fimbria-fornix. Most of these B1-derived cells gave rise to cells in the oligodendrocyte lineage, including local NG2+ progenitors, and pre-myelinating and myelinating oligodendrocytes. SVZ B1 cells also gave rise to a population of highly-branched S100beta+/glial fibrillary acidic protein (GFAP)+ cells in the striatum and septum, but no neuronal differentiation was observed. Interestingly, when demyelination was induced in the corpus callosum by a local injection of lysolecithin, an increased number of cells derived from SVZ B1 cells and stimulated to migrate and proliferate by EGF infusion differentiated into oligodendrocytes at the lesion site. This work indicates that EGF infusion can greatly expand the number of progenitors derived from the SVZ primary progenitors which migrate and differentiate into oligodendroglial cells. This expanded population could be used for the repair of white matter lesions.

Intracerebroventricular transplantation of human mesenchymal stem cells induced to secrete neurotrophic factors attenuates clinical symptoms in a mouse model of multiple sclerosis

Stem cell-based therapy holds great potential for future treatment of multiple sclerosis (MS). Bone marrow mesenchymal stem cells (MSCs) were previously reported to ameliorate symptoms in mouse MS models (experimental autoimmune encephalomyelitis, EAE). In this study, we induced MSCs to differentiate in vitro into neurotrophic factor-producing cells (NTFCs). Our main goal was to examine the clinical use of NTFCs on EAE symptoms. The NTFCs and MSCs were transplanted intracerebroventricularly (ICV) to EAE mice. We found that NTFCs transplantations resulted in a delay of symptom onset and increased animal survival. Transplantation of MSCs also exerted a positive effect but to a lesser extent. In vitro analysis demonstrated the NTFCs' capacity to suppress mice immune cells and protect neuronal cells from oxidative insult. Our results indicate that NTFCs-transplanted ICV delay disease symptoms of EAE mice, possibly via neuroprotection and immunomodulation, and may serve as a possible treatment to MS.

Adult neural stem cells expressing IL-10 confer potent immunomodulation and remyelination in experimental autoimmune encephalitis

Adult neural stem cells (aNSCs) derived from the subventricular zone of the brain show therapeutic effects in EAE, an animal model of the chronic inflammatory neurodegenerative disease MS; however, the beneficial effects are modest. One critical weakness of aNSC therapy may be an insufficient antiinflammatory effect. Here, we demonstrate that i.v. or i.c.v. injection of aNSCs engineered to secrete IL-10 (IL-10-aNSCs), a potent immunoregulatory cytokine, induced more profound functional and pathological recovery from ongoing EAE than that with control aNSCs. IL-10-aNSCs exhibited enhanced antiinflammatory effects in the periphery and inflammatory foci in the CNS compared with control aNSCs, more effectively reducing myelin damage, a hallmark of MS. When compared with mice treated with control aNSCs, those treated with IL-10-aNSCs demonstrated differentiation of transplanted cells into greater numbers of oligodendrocytes and neurons but fewer astrocytes, thus enhancing exogenous remyelination and neuron/axonal growth. Finally, IL-10-aNSCs converted a hostile environment to one supportive of neurons/oligodendrocytes, thereby promoting endogenous remyelination. Thus, aNSCs engineered to express IL-10 show enhanced ability to induce immune suppression, remyelination, and neuronal repair and may represent a novel approach that can substantially improve the efficacy of neural stem cell-based therapy in EAE/MS.

Towards personalized cell-replacement therapies for brain repair

The inability of the CNS to efficiently repair damage caused by trauma and neurodegenerative or demyelinating diseases has underlined the necessity for developing novel therapeutic strategies. Cell transplantation to replace lost neurons and the grafting of myelinating cells to repair demyelinating lesions are promising approaches for treating CNS injuries and demyelination. In this review, we will address the prospects of using stem cells or myelinating glial cells of the PNS, as well as olfactory ensheathing cells, in cell-replacement therapies. The recent generation of induced pluripotent stem cells from adult somatic cells by introduction of three or four genes controlling ‘stemness’ and their subsequent differentiation to desired phenotypes, constitutes a significant advancement towards personalized cell-replacement therapies.

Arterially perfused neurosphere-derived cells distribute outside the ischemic core in a model of transient focal ischemia and reperfusion in vitro

Background

Treatment with neural stem cells represents a potential strategy to improve functional recovery of post-ischemic cerebral injury. The potential benefit of such treatment in acute phases of human ischemic stroke depends on the therapeutic viability of a systemic vascular delivery route. In spite of the large number of reports on the beneficial effects of intracerebral stem cells injection in experimental stroke, very few studies demonstrated the effectiveness of the systemic intravenous delivery approach.

Metodology/Principal Findings

We utilized a novel in vitro model of transient focal ischemia to analyze the brain distribution of neurosphere-derived cells (NCs) in the early 3 hours that follow transient occlusion of the medial cerebral artery (MCA). NCs obtained from newborn C57/BL6 mice are immature cells with self-renewal properties that could differentiate into neurons, astrocytes and oligodendrocytes. MCA occlusion for 30 minutes in the in vitro isolated guinea pig brain preparation was followed by arterial perfusion with 1×10⁶ NCs charged with a green fluorescent dye, either immediately or 60 minutes after reperfusion onset. Changes in extracellular pH and K⁺ concentration during and after MCAO were measured through ion-sensitive electrodes.

Conclusion/Significance

It is demonstrated that NCs injected through the vascular system do not accumulate in the ischemic core and preferentially distribute in non-ischemic areas, identified by combined electrophysiological and morphological techniques. Direct measurements of extracellular brain ions during and after MCA occlusion suggest that anoxia-induced tissue changes, such as extracellular acidosis, may prevent NCs from entering the ischemic area in our in vitro model of transitory focal ischemia and reperfusion suggesting a role played by the surrounding microenviroment in driving NCs outside the ischemic core. These findings strongly suggest that the potential beneficial effect of NCs in experimental focal brain ischemia is not strictly dependent on their homing into the ischemic region, but rather through a bystander mechanism possibly mediated by the release of neuroprotective factors in the peri-infarct region.

The biology of CNS remyelination: the key to therapeutic advances

Remyelination, the process by which new myelin sheaths are restored to demyelinated axons, represents one of the most compelling examples of adult multipotent progenitor cells contributing to regeneration of the injured CNS. This process can occur with remarkable efficiency in both clinical disease, such as multiple sclerosis, and in experimental models, revealing an impressive ability of the adult CNS to repair itself. However, the inconsistency of remyelination in multiple sclerosis, and the loss of axonal integrity that results from its failure, makes enhancement of remyelination an important therapeutic objective. Identifying potential targets requires a detailed understanding of the cellular and molecular mechanisms of remyelination. A critical step in achieving effective remyelination is the differentiation of precursor cells into mature oligodendrocytes. In experimental models of demyelinating disease in aged animals, as well as in multiple sclerosis, such differentiation appears to be impaired. This is due, at least in part, to changes in environmental signals governing remyelination. In particular, myelin debris within lesions appears to contain powerful inhibitors of precursor cell differentiation. Efficient removal of myelin debris by macrophages may thus facilitate differentiation and permit successful remyelination of damaged axons. This may represent a promising therapeutic target for promoting remyelination in multiple sclerosis and thus limiting the accumulation of irreversible neurological disability.

Intranasal HB-EGF administration favors adult SVZ cell mobilization to demyelinated lesions in mouse corpus callosum

In the adult rodent brain, the subventricular zone (SVZ) represents a special niche for neural stem cells; these cells proliferate and generate neural progenitors. Most of these migrate along the rostral migratory stream to the olfactory bulb, where they differentiate into interneurons. SVZ-derived progenitors can also be recruited spontaneously to damaged brain areas to replace lost cells, including oligodendrocytes in demyelinated lesions. In this study, we searched for factors able to enhance this spontaneous recruitment of endogenous progenitors. Previous studies have suggested that epidermal growth factor (EGF) could stimulate proliferation, migration, and glial differentiation of SVZ progenitors. In the present study we examined EGF influence on endogenous SVZ cell participation to brain repair in the context of demyelinated lesions. We induced a focal demyelinated lesion in the corpus callosum by lysolecithin injection and showed that intranasal heparin-binding epidermal growth factor (HB-EGF) administration induces a significant increase in SVZ cell proliferation together with a stronger SVZ cell mobilization toward the lesions. Besides, HB-EGF causes a shift of SVZ-derived progenitor cell differentiation toward the astrocytic lineage. However, due to the threefold increase in cell recruitment by EGF treatment, the absolute number of SVZ-derived oligodendrocytes in the lesion of treated mice is higher than in controls. These results suggest that enhancing SVZ cell proliferation could be part of future strategies to promote SVZ progenitor cell mobilization toward brain lesions.

Stem cells ameliorate EAE via an indoleamine 2,3-dioxygenase (IDO) mechanism

Syngeneic, pluripotent Lin(-)Sca1(+) bone marrow stem cells (SC), transferred to mice with experimental autoimmune encephalomyelitis, a model of multiple sclerosis, enhanced recovery, prevented relapses and promoted myelin repair. SC-treated mice showed elevated interferon-gamma production and induction of indoleamine 2,3-dioxygenase (IDO) in CD11c(+) dendritic cells (DC). IDO induction was specific since in the presence of IDO-producing CD11c(+) DC, PLP stimulated T cell proliferation was inhibited and the IDO-inhibitor, 1-MT, abrogated the SC effect. Relapse prevention during chronic disease correlated with decreased responsiveness to PLP(178-191) and MBP(85-99). Thus, pluripotent SC induce IDO in DC leading to inhibition of antigen reactivity and spreading in EAE.

Cross-talk between inflammatory cytokines and neural stem cells: a bidirectional relation

Neural stem/precursor cells (NSCs/NPCs) are immature progenitors both in the developing and adult nervous system. They are considered to replace damaged cells within the CNS as part of the endogenous repair mechanism following an injury. Moreover, their transplantation has been proposed as a means of cell-replacement therapy. Both endogenous and transplanted NPCs have to cope with a number of factors within the damaged CNS environment, such as inflammatory mediators, free radicals and so on. Among these factors, cytokines are key molecules during inflammatory and/or degenerative processes in the CNS. The survival, migration, growth and differentiation of NPCs are differentially affected by a number of both pro- and anti-inflammatory cytokines. On the other hand, NPCs exert an immunomodulatory effect that inhibits CNS inflammation. Before any human application of NPC-based therapies, these cells should be used in a way that both their regenerative and immunologic properties are utilized.

Hyperbaric oxygenation in peripheral nerve repair and regeneration

Peripheral nerves are essential connections between the central nervous system and muscles, autonomic structures and sensory organs. Their injury is one of the major causes for severe and longstanding impairment in limb function. Acute peripheral nerve lesion has an important inflammatory component and is considered as ischemia-reperfusion (IR) injury. Surgical repair has been the standard of care in peripheral nerve lesion. It has reached optimal technical development but the end results still remain unpredictable and complete functional recovery is rare. Nevertheless, nerve repair is not primarily a mechanical problem and microsurgery is not the only key to success. Lately, there have been efforts to develop alternatives to nerve graft. Work has been carried out in basal lamina scaffolds, biologic and non-biologic structures in combination with neurotrophic factors and/or Schwann cells, tissues, immunosuppressive agents, growth factors, cell transplantation, principles of artificial sensory function, gene technology, gangliosides, implantation of microchips, hormones, electromagnetic fields and hyperbaric oxygenation (HBO). HBO appears to be a beneficial adjunctive treatment for surgical repair in the acute peripheral nerve lesion, when used at lower pressures and in a timely fashion (<6 hours).

Remyelination in multiple sclerosis

Remyelination is the phenomenon by which new myelin sheaths are generated around axons in the adult central nervous system (CNS). This follows the pathological loss of myelin in diseases like multiple sclerosis (MS). Remyelination can restore conduction properties to axons (thereby restoring neurological function) and is increasingly believed to exert a neuroprotective role on axons. Remyelination occurs in many MS lesions but becomes increasingly incomplete/inadequate and eventually fails in the majority of lesions and patients. Efforts to understand the causes for this failure of regeneration have fueled research into the biology of remyelination and the complex, interdependent cellular and molecular factors that regulate this process. Examination of the mechanisms of repair of experimental lesions has demonstrated that remyelination occurs in two major phases. The first consists of colonization of lesions by oligodendrocyte progenitor cells (OPCs), the second the differentiation of OPCs into myelinating oligodendrocytes that contact demyelinated axons to generate functional myelin sheaths. Several intracellular and extracellular molecules have been identified that mediate these two phases of repair. Theoretically, the repair of demyelinating lesions can be promoted by enhancing the intrinsic repair process (by providing one or more remyelination-enhancing factors or via immunoglobulin therapy). Alternatively, endogenous repair can be bypassed by introducing myelinogenic cells into demyelinated areas; several cellular candidates have been identified that can mediate repair of experimental demyelinating lesions. Future challenges confronting therapeutic strategies to enhance remyelination will involve the translation of findings from basic science to clinical demyelinating disease.

Neural transplantation of human MSC and NT2 cells in the twitcher mouse model

BACKGROUND

Accumulating evidence has demonstrated that the NT2 embryonal carcinoma cell line and multipotential stem cells found in BM, mesenchymal stromal cells (MSC), have the ability to differentiate into a wide variety of cell types. This study was designed to explore the efficacy of these two human stem cell types as a graft source for the treatment of demyelinating disorders such as Krabbe's disease and multiple sclerosis (MS).

METHODS

We examined the engraftment and in vivo differentiation of adult MSC and NT2 cells after transplantation into two demyelinating environments, the neonatal and postnatal twitcher mouse brain.

RESULTS

Both types of xenografts led to anatomical integration, without tumor formation, and remained viable in the normal and twitcher mouse brain, showing differentiation into neurons, astrocytes and oligodendrocytes.

DISCUSSION

This study represents a platform for further stem cell transplantation studies in the twitcher model and potentially has important therapeutic implications.

Future of multiple sclerosis therapy: combining antigen-specific immunotherapy with strategies to promote myelin repair

Persistent CNS inflammation and the failure of myelin repair during multiple sclerosis (MS) trigger a progressive deterioration in neurophysiological function and permanent clinical debilitation. Current treatment consists of immunosuppressive therapies targeted against the immune response, which have only been moderately successful in ameliorating disease relapses and have little or no benefit in slowing disease progression or enhancing remyelination. Recent breakthroughs have revealed new targets and more selective techniques for inhibiting autoreactive T-cell responses and promoting lesion repair in animal models of MS. In light of these new findings and the limitations of current treatments, the authors hypothesize that the future of MS therapy will progress towards the development of a combinatorial therapeutic strategy that consists of specific tolerance of autoreactive T cells, myelin repair and axonal protection.

Baculovirus-mediated gene delivery into Mammalian cells does not alter their transcriptional and differentiating potential but is accompanied by early viral gene expression

Gene delivery to neural cells is central to the development of transplantation therapies for neurological diseases. In this study, we used a baculovirus derived from the domesticated silk moth, Bombyx mori, as vector for transducing a human cell line (HEK293) and primary cultures of rat Schwann cells. Under optimal conditions of infection with a recombinant baculovirus containing the reporter green fluorescent protein gene under mammalian promoter control, the infected cells express the transgene with high efficiency. Toxicity assays and transcriptome analyses suggest that baculovirus infection is not cytotoxic and does not induce differential transcriptional responses in HEK293 cells. Infected Schwann cells retain their characteristic morphological and molecular phenotype as determined by immunocytochemistry for the marker proteins S-100, glial fibrillary acidic protein, and p75 nerve growth factor receptor. Moreover, baculovirus-infected Schwann cells are capable of differentiating in vitro and express the P0 myelination marker. However, transcripts for several immediate-early viral genes also accumulate in readily detectable levels in the transduced cells. This transcriptional activity raises concerns regarding the long-term safety of baculovirus vectors for gene therapy applications. Potential approaches for overcoming the identified problem are discussed.