Structure-specific patterns of neural stem cell engraftment after transplantation in the adult mouse brain

Brain transplantation of genetically corrected Sanfilippo type B neural stem cells induces partial cross-correction of the disease

Sanfilippo syndrome type B (mucopolysaccharidosis type IIIB) is a recessive genetic disorder that severely affects the brain due to a deficiency in the enzyme α-N-acetylglucosaminidase (NAGLU), leading to intra-lysosomal accumulation of partially degraded heparan sulfate. There are no effective treatments for this disorder. In this project, we carried out an ex vivo correction of neural stem cells derived from Naglu -/- mice (iNSCs) induced pluripotent stem cells (iPSC) using a modified enzyme in which human NAGLU is fused to an insulin-like growth factor II receptor binding peptide in order to improve enzyme uptake. After brain transplantation of corrected iNSCs into Naglu -/- mice and long-term evaluation of their impact, we successfully detected NAGLU-IGFII activity in all transplanted animals. We found decreased lysosomal accumulation and reduced astrocytosis and microglial activation throughout transplanted brains. We also identified a novel neuropathological phenotype in untreated Naglu -/- brains with decreased levels of the neuronal marker Map2 and accumulation of synaptophysin-positive aggregates. Upon transplantation, we restored levels of Map2 expression and significantly reduced formation of synaptophysin-positive aggregates. Our findings suggest that genetically engineered iNSCs can be used to effectively deliver the missing enzyme to the brain and treat Sanfilippo type B-associated neuropathology.

Molecular Imaging of Stem Cells

Regenerative medicine with the use of stem cells has appeared as a potential therapeutic alternative for many disease states. Despite initial enthusiasm, there has been relatively slow transition to clinical trials. In large part, numerous questions remain regarding the viability, biology and efficacy of transplanted stem cells in the living subject. The critical issues highlighted the importance of developing tools to assess these questions. Advances in molecular biology and imaging have allowed the successful non-invasive monitoring of transplanted stem cells in the living subject. Over the years these methodologies have been updated to assess not only the viability but also the biology of transplanted stem cells. In this review, different imaging strategies to study the viability and biology of transplanted stem cells are presented. Use of these strategies will be critical as the different regenerative therapies are being tested for clinical use.

Stem Cell Therapy for the Central Nervous System in Lysosomal Storage Diseases

Neurological diseases with genetic etiologies result in the loss or dysfunction of neural cells throughout the CNS. At present, few treatment options exist for the majority of neurogenetic diseases. Stem cell transplantation (SCT) into the CNS has the potential to be an effective treatment modality because progenitor cells may replace lost cells in the diseased brain, provide multiple trophic factors, or deliver missing proteins. This review focuses on the use of SCT in lysosomal storage diseases (LSDs), a large group of monogenic disorders with prominent CNS disease. In most patients the CNS disease results in intellectual disability that is refractory to current standard-of-care treatment. A large amount of preclinical work on brain-directed SCT has been performed in rodent LSD models. Cell types that have been used for direct delivery into the CNS include neural stem cells, embryonic and induced pluripotent stem cells, and mesenchymal stem cells. Hematopoietic stem cells have been an effective therapy for the CNS in a few LSDs and may be augmented by overexpression of the missing gene. Current barriers and potential strategies to improve SCT for translation into effective patient therapies are discussed.

Exogenous Neural Stem Cells Transplantation as a Potential Therapy for Photothrombotic Ischemia Stroke in Kunming Mice Model

Stroke is considered as the second leading cause of death worldwide. The survivors of stroke experience different levels of impairment in brain function resulting in debilitating disabilities. Current therapies for stroke are primarily palliative and may be effective in only a small population of stroke patients. In this study, we explore the transplantation of exogenous neural stem cells (NSCs) as the potential therapy for the photothrombotic ischemia stroke in a Kunming mice model. After stroke, mice receiving NSC transplantation demonstrated a better recovery of brain function during the neurobehavioral tests. Histology analysis of the brain samples from NSC transplanted mice demonstrated a reduction of brain damage caused by stroke. Moreover, immunofluorescence assay for biomarkers in brain sections confirmed that transplanted NSCs indeed differentiated to neurons and astrocytes, consistent with the improved brain function after stroke. Taken together, our data suggested that exogenous NSC transplantation could be a promising therapy for stroke.

In Vivo Tracking of Human Neural Progenitor Cells in the Rat Brain Using Magnetic Resonance Imaging Is Not Enhanced by Ferritin Expression

Rapid growth in the field of stem cell research has generated a lot of interest in their therapeutic use, especially in the treatment of neurodegenerative diseases. Specifically, human neural progenitor cells (hNPCs), unique in their capability to differentiate into cells of the neural lineage, have been widely investigated due to their ability to survive, thrive, and migrate toward injured tissues. Still, one of the major roadblocks for clinical applicability arises from the inability to monitor these cells following transplantation. Molecular imaging techniques, such as magnetic resonance imaging (MRI), have been explored to assess hNPC transplant location, migration, and survival. Here we investigated whether inducing hNPCs to overexpress ferritin (hNPCs(Fer)), an iron storage protein, is sufficient to track these cells long term in the rat striatum using MRI. We found that increased hypointensity on MRI images could establish hNPC(Fer) location. Unexpectedly, however, wild-type hNPC transplants were detected in a similar manner, which is likely due to increased iron accumulation following transplantation-induced damage. Hence, we labeled hNPCs with superparamagnetic iron oxide (SPIO) nanoparticles to further increase iron content in an attempt to enhance cell contrast in MRI. SPIO-labeling of hNPCs (hNPCs-SPIO) achieved increased hypointensity, with significantly greater area of decreased T2* compared to hNPC(Fer) (p < 0.0001) and all other controls used. However, none of the techniques could be used to determine graft rejection in vivo, which is imperative for understanding cell behavior following transplantation. We conclude that in order for cell survival to be monitored in preclinical and clinical settings, another molecular imaging technique must be employed, including perhaps multimodal imaging, which would utilize MRI along with another imaging modality.

Viability, differentiation capacity, and detectability of super-paramagnetic iron oxide-labeled muscle precursor cells for magnetic-resonance imaging

Cell therapies are a promising approach for the treatment of a variety of human conditions including stress urinary incontinence, but their success greatly depends on the biodistribution, migration, survival, and differentiation of the transplanted cells. Noninvasive in vivo cell tracking therefore presents an important aspect for translation of such a procedure into the clinics. Upon labeling with superparamagnetic iron oxide (SPIO) nanoparticles, cells can be tracked by magnetic resonance imaging (MRI), but possible adverse effect of the labeling have to be considered when labeling stem cells with SPIOs. In this study, human muscle precursor cells (hMPC) were labeled with increasing concentrations of SPIO nanoparticles (100-1600 μg/mL) and cell viability and differentiation capacity upon labeling was assessed in vitro. While a linear dependence between cell viability and nanoparticle concentration could be observed, differentiation capacity was not affected by the presence of SPIOs. Using a nude mouse model, a concentration (400 μg/mL) could be defined that allows reliable detection of hMPCs by MRI but does not influence myogenic in vivo differentiation to mature and functional muscle tissue. This suggests that such an approach can be safely used in a clinical setting to track muscle regeneration in patients undergoing cell therapy without negative effects on the functionality of the bioengineered muscle.

Neuroprotective effect of buyang huanwu decoction on rat ischemic/reperfusion brain damage by promoting migration of neural precursor cells

Buyang Huanwu Decoction (BYHWD) is a classic formula widely used for treating stroke-induced disability, the highest morbidity of neurological disorders in China. However, the mechanism of its neuroprotection has not been fully clarified. Previous reports indicated that BYHWD may promote growth and differentiation of neural precursor cells (NPCs). The present study focused on the effects of BYHWD on migration of NPCs in rats with middle cerebral artery occlusion (MCAO). Rats were treated with different doses of BYHWD (12 and 24 grams/kg) from day 1 to day 21 after model building. BYHWD could increase the survival rate and decrease neurological scores and infarct volume as compared with the vehicle-treated MCAO rats. Moreover, BYHWD treatment significantly increased 5-bromo-2-deoxyuridine (BrdU)-positive cells in the subventricular zone (SVZ), subgranular zone (SGZ), and corpus striatum (CS) of the infarct brain. Interestingly, BYHWD could markedly enhance BrdU(+)/doublecortin(+) cells not only in the SVZ and SGZ but also in CS, by up-regulating the protein expression of migration activators, including stromal cell derived factor-1, CXC chemokine receptor 4, vascular endothelial growth factor, Reelin, and brain-derived neurotrophic factor in the ipsilateral infarct area after MCAO. In addition, BYHWD treatment was able to promote the neuronal differentiation, which was closely related to the migratory process of NPCs in MCAO rats. These findings offer evidence for the first time that BYHWD may exert its neuroprotective effects partially by promotion of NPCs migration to ischemic brain areas.

High-resolution magnetic resonance microscopy and diffusion tensor imaging to assess brain structural abnormalities in the murine mucopolysaccharidosis VII model

High-resolution microscopic magnetic resonance imaging (μMRI) and diffusion tensor imaging (DTI) were performed to characterize brain structural abnormalities in a mouse model of mucopolysaccharidosis type VII (MPS VII). Microscopic magnetic resonance imaging demonstrated a decrease in the volume of anterior commissure and corpus callosum and a slight increase in the volume of the hippocampus in MPS VII versus wild-type mice. Diffusion tensor imaging indices were analyzed in gray and white matter. In vivo and ex vivo DTI demonstrated significantly reduced fractional anisotropy in the anterior commissure, corpus callosum, external capsule, and hippocampus in MPS VII versus control brains. Significantly increased mean diffusivity was also found in the anterior commissure and corpus callosum from ex vivo DTI. Significantly reduced linear anisotropy was observed from the hippocampus from in vivo DTI, whereas significantly decreased planar anisotropy and spherical anisotropy were observed in the external capsule from only ex vivo DTI. There were corresponding morphologic differences in the brains of MPS VII mice by hematoxylin and eosin staining. Luxol fast blue staining demonstrated less intense staining of the corpus callosum and external capsule; myelin abnormalities in the corpus callosum were also demonstrated quantitatively in toluidine blue-stained sections and confirmed by electron microscopy. These results demonstrate the potential for μMRI and DTI for quantitative assessment of brain pathology in murine models of brain diseases.

Engraftment of nonintegrating neural stem cells differentially perturbs cortical activity in a dose-dependent manner

Neural stem cell (NSC) therapy represents a potentially powerful approach for gene transfer in the diseased central nervous system. However, transplanted primary, embryonic stem cell- and induced pluripotent stem cell-derived NSCs generate largely undifferentiated progeny. Understanding how physiologically immature cells influence host activity is critical to evaluating the therapeutic utility of NSCs. Earlier inquiries were limited to single-cell recordings and did not address the emergent properties of neuronal ensembles. To interrogate cortical networks post-transplant, we used voltage sensitive dye imaging in mouse neocortical brain slices, which permits high temporal resolution analysis of neural activity. Although moderate NSC engraftment largely preserved host physiology, subtle defects in the activation properties of synaptic inputs were induced. High-density engraftment severely dampened cortical excitability, markedly reducing the amplitude, spatial extent, and velocity of propagating synaptic potentials in layers 2-6. These global effects may be mediated by specific disruptions in excitatory network structure in deep layers. We propose that depletion of endogenous cells in engrafted neocortex contributes to circuit alterations. Our data provide the first evidence that nonintegrating cells cause differential host impairment as a function of engrafted load. Moreover, they emphasize the necessity for efficient differentiation methods and proper controls for engraftment effects that interfere with the benefits of NSC therapy.

Transplantation of CD15-enriched murine neural stem cells increases total engraftment and shifts differentiation toward the oligodendrocyte lineage

Neural stem cell (NSC) transplantation is a promising therapeutic approach for neurological diseases. However, only a limited number of cells can be transplanted into the brain, resulting in relatively low levels of engraftment. This study investigated the potential of using a cell surface marker to enrich a primary NSC population to increase stable engraftment in the recipient brain. NSCs were enriched from the neonatal mouse forebrain using anti-CD15 (Lewis X antigen, or SSEA-1) in a "gentle" fluorescence-activated cell sorting protocol, which yielded >98% CD15-positive cells. The CD15-positive cells differentiated into neurons, astrocytes, and oligodendrocytes in vitro, after withdrawal of growth factors, demonstrating multipotentiality. CD15-positive cells were expanded in vitro and injected bilaterally into the ventricles of neonatal mice. Cells from enriched and unenriched donor populations were found throughout the neuraxis, in both neurogenic and non-neurogenic regions. Total engraftment was similar at 7 days postinjection, but by 28 days postinjection, after brain organogenesis was complete, the survival of donor cells was significantly increased in CD15-enriched grafts over the unenriched cell grafts. The engrafted cells were heterogeneous in morphology and differentiated into all three neural lineages. Furthermore, in the CD15-enriched grafts, there was a significant shift toward differentiation into oligodendrocytes. This strategy may allow better delivery of therapeutic cells to the developing central nervous system and may be particularly useful for treating diseases involving white matter lesions.

Evidence for crossing the blood barrier of adult rat brain by human adipose-derived mesenchymal stromal cells during a 6-month period of post-transplantation

BACKGROUND AIMS

Therapeutic promises of adult stem cells have been overshadowed by an elicited immune response, low maintenance of implanted cells or concerns regarding their migration to non-target sites. These problems might be lessened by the use of immune privilege cells and tissues for implantation.

METHODS

In this study, human adipose-derived mesenchymal stromal cells (hADMSCs) were stably transfected with a vector containing Turbo green fluorescent protein (GFP) and JRed, which allows tracing the cells after transplantation. Labeled hADMSCs were transplanted into the adult rat brain followed by assessment of their survival and migration during 6 months after transplantation.

RESULTS

Results indicate that there were no postsurgical complications, and the animals thrived after transplantation. The lesions of the surgical process were remarkable at the first weeks, and a high number of transplanted cells were accumulated around them. Cell populations declined over time as they partly migrated away from the injection sites; nonetheless, they were detectable at each examination time point. Although the cells could survive and remain at the injection site for up to 6 months, some of them drifted to spleen, which is an indication of their ability to cross the blood-brain barrier.

CONCLUSIONS

Despite the high survival rate of hADMSCs in the xenogenic condition, which is an ideal criterion in cell therapy, irregular migration tendency must be handled with caution.

The application of super paramagnetic iron oxide-labeled mesenchymal stem cells in cell-based therapy

Mesenchymal stem cell (MSC)-based therapy has great potential for tissue regeneration. However, being able to monitor the in vivo behavior of implanted MSCs and understand the fate of these cells is necessary for further development of successful therapies and requires an effective, non-invasive and non-toxic technique for cell tracking. Super paramagnetic iron oxide (SPIO) is an idea label and tracer of MSCs. MRI can be used to follow SPIO-labeled MSCs and has been proposed as a gold standard for monitoring the in vivo biodistribution and migration of implanted SPIO-labeled MSCs. This review discusses the biological effects of SPIO labeling on MSCs and the therapeutic applications of local or systemic delivery of these labeled cells.

Personalized nanomedicine advancements for stem cell tracking

Recent technological developments in biomedicine have facilitated the generation of data on the anatomical, physiological and molecular level for individual patients and thus introduces opportunity for therapy to be personalized in an unprecedented fashion. Generation of patient-specific stem cells exemplifies the efforts toward this new approach. Cell-based therapy is a highly promising treatment paradigm; however, due to the lack of consistent and unbiased data about the fate of stem cells in vivo, interpretation of therapeutic effects remains challenging hampering the progress in this field. The advent of nanotechnology with a wide palette of inorganic and organic nanostructures has expanded the arsenal of methods for tracking transplanted stem cells. The diversity of nanomaterials has revolutionized personalized nanomedicine and enables individualized tailoring of stem cell labeling materials for the specific needs of each patient. The successful implementation of stem cell tracking will likely be a significant driving force that will contribute to the further development of nanotheranostics. The purpose of this review is to emphasize the role of cell tracking using currently available nanoparticles.

Differential effects of distinct central nervous system regions on cell migration and axonal extension of neural precursor transplants

Transplantation of neural precursor cells (NPCs) is a promising therapeutic strategy in CNS injury. However, the adult CNS lacks instructive signals present during development and, depending on the region and type of transplant, may be inhibitory for neuron generation and axonal growth. We examined the effects of the white matter in different regions of the adult CNS on the properties of NPC transplants with respect to cell survival, differentiation, migration, and axonal growth. NPCs were prepared from day 13.5 embryonic spinal cord of transgenic rats that express the human placental alkaline phosphatase (AP) reporter. These NPCs were injected unilaterally into the cervical spinal cord white matter and into the corpus callosum of adult rats and were analyzed immunohistochemically 2 weeks later. NPCs survived in both regions and differentiated into astrocytes, oligodendrocytes, and neurons, with no apparent differences in survival or phenotypic composition. However, in the spinal cord white matter, graft-derived cells, identified as precursors and glial cells, migrated from the injection site rostrally and caudally, whereas, in the corpus callosum, graft-derived cells did not migrate and remained at the injection site. Importantly, graft-derived neurons extended axons from the grafting site along the corpus callosum past the midline, entering into the contralateral side of the corpus callosum. These results demonstrate dramatic differences between white matter regions in the spinal cord and brain with respect to cell migration and axonal growth and underscore the importance of considering the effects of the local CNS environment in the design of effective transplantation strategies.

Current challenges for the advancement of neural stem cell biology and transplantation research

Transplantation of neural stem cells (NSC) is hoped to become a promising primary or secondary therapy for the treatment of various neurodegenerative disorders of the central nervous system (CNS), as demonstrated by multiple pre-clinical animal studies in which functional recovery has already been demonstrated. However, for NSC therapy to be successful, the first challenge will be to define a transplantable cell population. In the first part of this review, we will briefly discuss the main features of ex vivo culture and characterisation of NSC. Next, NSC grafting itself may not only result in the regeneration of lost tissue, but more importantly has the potential to improve functional outcome through many bystander mechanisms. In the second part of this review, we will briefly discuss several pre-clinical studies that contributed to a better understanding of the therapeutic potential of NSC grafts in vivo. However, while many pre-clinical animal studies mainly report on the clinical benefit of NSC grafting, little is known about the actual in vivo fate of grafted NSC. Therefore, the third part of this review will focus on non-invasive imaging techniques for monitoring cellular grafts in the brain under in vivo conditions. Finally, as NSC transplantation research has evolved during the past decade, it has become clear that the host micro-environment itself, either in healthy or injured condition, is an important player in defining success of NSC grafting. The final part of this review will focus on the host environmental influence on survival, migration and differentiation of grafted NSC.

Magnetic resonance imaging of ferumoxide-labeled mesenchymal stem cells in cartilage defects: in vitro and in vivo investigations

The purpose of this study was to (1) compare three different techniques for ferumoxide labeling of mesenchymal stem cells (MSCs), (2) evaluate if ferumoxide labeling allows in vivo tracking of matrix-associated stem cell implants (MASIs) in an animal model, and (3) compare the magnetic resonance imaging (MRI) characteristics of ferumoxide-labeled viable and apoptotic MSCs. MSCs labeled with ferumoxide by simple incubation, protamine transfection, or Lipofectin transfection were evaluated with MRI and histopathology. Ferumoxide-labeled and unlabeled viable and apoptotic MSCs in osteochondral defects of rat knee joints were evaluated over 12 weeks with MRI. Signal to noise ratios (SNRs) of viable and apoptotic labeled MASIs were tested for significant differences using t-tests. A simple incubation labeling protocol demonstrated the best compromise between significant magnetic resonance signal effects and preserved cell viability and potential for immediate clinical translation. Labeled viable and apoptotic MASIs did not show significant differences in SNR. Labeled viable but not apoptotic MSCs demonstrated an increasing area of T2 signal loss over time, which correlated to stem cell proliferation at the transplantation site. Histopathology confirmed successful engraftment of viable MSCs. The engraftment of iron oxide-labeled MASIs by simple incubation can be monitored over several weeks with MRI. Viable and apoptotic MASIs can be distinguished via imaging signs of cell proliferation at the transplantation site.

Effects of neonatal neural progenitor cell implantation on adult neuroanatomy and cognition in the Ts65Dn model of Down syndrome

As much of the aberrant neural development in Down syndrome (DS) occurs postnatally, an early opportunity exists to intervene and influence life-long cognitive development. Recent success using neural progenitor cells (NPC) in models of adult neurodegeneration indicate such therapy may be a viable option in diseases such as DS. Murine NPC (mNPC, C17.2 cell line) or saline were implanted bilaterally into the dorsal hippocampus of postnatal day 2 (PND 2) Ts65Dn pups to explore the feasibility of early postnatal treatment in this mouse model of DS. Disomic littermates provided karyotype controls for trisomic pups. Pups were monitored for developmental milestone achievement, and then underwent adult behavior testing at 14 weeks of age. We found that implanted mNPC survived into adulthood and migrated beyond the implant site in both karyotypes. The implantation of mNPC resulted in a significant increase in the density of dentate granule cells. However, mNPC implantation did not elicit cognitive changes in trisomic mice either neonatally or in adulthood. To the best of our knowledge, these results constitute the first assessment of mNPC as an early intervention on cognitive ability in a DS model.

Neural stem cells modified by a hypoxia-inducible VEGF gene expression system improve cell viability under hypoxic conditions and spinal cord injury

STUDY DESIGN

An in vitro neural hypoxia model and rat spinal cord injury (SCI) model were used to assess the regulation of therapeutic vascular endothelial growth factor (VEGF) gene expression in mouse neural stem cells (mNSCs) by the EPO (erythropoietin) enhancer or RTP801 promoter.

OBJECTIVE

To increase VEGF gene expression in mNSCs under hypoxic conditions in SCI lesions but avoid unwanted overexpression of VEGF in normal sites, we developed a hypoxia-inducible gene expression system consisting of the EPO enhancer and RTP801 promoter fused to VEGF or the luciferase gene, then transfected into mNSCs.

SUMMARY OF BACKGROUND DATA

On the basis of the ischemic response in the injured area, poor cell survival at the transplantation site is a consistent problem with NSC transplantation after SCI. Although VEGF directly protects neurons and enhances neurite outgrowth, uncontrolled overexpression of VEGF in uninjured tissue may cause serious adverse effects. To effectively improve NSC survival in ischemic sites after transplantation, we evaluated mNSCs modified by a hypoxia-inducible VEGF gene expression system in an SCI model.

METHODS

Hypoxia-inducible luciferase or VEGF plasmids were constructed using the EPO enhancer or RTP801 promoter. The effect of these systems on targeted gene expression and cell viability was evaluated in mNSCs in both hypoxic in vitro injury and a rat SCI model in vivo.

RESULTS

The gene expression system containing the EPO enhancer or RTP801 promoter significantly increased the expression of the luciferase reporter gene and therapeutic VEGF gene under hypoxic conditions. The Epo-SV-VEGF plasmid transfection group had significantly fewer apoptotic cells in vitro. This system also augmented cell viability in the in vivo SCI model.

CONCLUSION

These results strongly suggest the potential utility of mNSCs modified by a hypoxia-inducible VEGF gene expression system in the development of effective stem cell transplantation protocols in SCI.

Differentiation of neural stem cells influences their chemotactic responses to vascular endothelial growth factor

Although much effort has been devoted to the delineation of factors involved in the migration of neural stem/progenitor cells (NSCs), the relationship between the chemotactic response and the differentiation status of these cells remains elusive. In the present study, we found that NSCs in varying differentiation states possess different chemotactic responses to vascular endothelial growth factor (VEGF): first, the number of chemotaxing NSCs and the optimal concentrations of VEGF that induced the peak migration vary greatly; second, time-lapse video analysis shows that NSCs at certain differentiation states migrate more efficiently toward VEGF, although the migration speed remains unchanged irrespective of cell states; third, the phosphorylation status of Akt, ERK1/2, SAPK/JNK, and p38MAPK is closely related to the differentiation levels of NSCs subjected to VEGF; and, finally, although inhibition of ERK1/2 signaling significantly attenuates VEGF-stimulated transfilter migration of both undifferentiated and differentiating NSCs, NSCs show normal chemotactic response after treatment with inhibitors of SAPK/JNK or p38MAPK. Meanwhile, interference with PI3K/Akt signaling prevents only NSCs of 12 hr differentiation, but not NSCs of 1 day or 3 days differentiation, from migrating in response to VEGF. Moreover, blocking of PI3K/Akt or MAPK signaling impairs the migration efficiency and/or speed, the extent of which depends on the cell differentiation status. Collectively, these results demonstrate that differentiation of NSCs influences their chemotactic responses to VEGF: NSCs in varying differentiation states have different migratory capacities, thereby shedding light on optimization of the therapeutic potential of NSCs to be employed for neural regeneration after injury.

In vivo and ex vivo MR imaging of slowly cycling melanoma cells

Slowly cycling cells are believed to play a critical role in tumor progression and metastatic dissemination. The goal of this study was to develop a method for in vivo detection of slowly cycling cells. To distinguish these cells from more rapidly proliferating cells that constitute the vast majority of cells in tumors, we used the well-known effect of label dilution due to division of cells with normal cycle and retention of contrast agent in slowly dividing cells. To detect slowly cycling cells, melanoma cells were labeled with iron oxide particles. After labeling, we observed dilution of contrast agent in parallel with cell proliferation in the vast majority of normally cycling cells. A small and distinct subpopulation of iron-retaining cells was detected by flow cytometry after 20 days of in vitro proliferation. These iron-retaining cells exhibited high expression of a biological marker of slowly cycling cells, JARID1B. After implantation of labeled cells as xenografts into immunocompromised mice, iron-retaining cells were detected in vivo and ex vivo by magnetic resonance imaging that was confirmed by Prussian Blue staining. Magnetic resonance imaging detects not only iron retaining melanoma cells but also iron positive macrophages. Proposed method opens up opportunities to image subpopulation of melanoma cells, which is critical for continuous tumor growth.

The role of stem cells in tumor targeting and growth suppression of gliomas

Glioma remains the most challenging solid organ tumor to treat successfully. Based on the capacity of stem cells to migrate extensively and target invading glioma cells, the transplantation of stem cells as a cell-based delivery system may provide additional tools for the treatment of gliomas. In addition to the use of modified stem cells for the delivery of therapeutic agents, unmodified stem cells have been shown to have growth-suppressing effects on tumors in vitro and in vivo. This review outlines the probable factors involved in tumor tropism and tumor growth suppression, with a specific focus on the use of unmodified stem cells in the treatment of gliomas. Based on these and further future data, clinical trials may be justified.

lacZ as a genetic reporter for real-time MRI

Molecular imaging based on MRI is currently hampered by the lack of genetic reporters for in vivo imaging. We determined that the commercially available substrate S-Gal can be used to detect genetically engineered beta-galactosidase expressing cells by MRI. The effect and specificity of the reaction between beta-galactosidase and S-Gal on MRI contrast were determined both in vitro and in vivo. beta-galactosidase activity in the presence of S-Gal resulted in enhanced T(2) and T*(2) MR-contrast, which was amplified with increasing magnetic field strengths (4.7-17.6 T) in phantom studies. Using both lacZ(+) transgenic animals and lacZ(+) tissue transplants, we were able to detect labeled cells in live animals in real time. Similar to phantom studies, detection of the labeled cells/tissues in vivo was enhanced at high magnetic fields. These results demonstrate that the genetic reporter, lacZ, can be used as an in vivo marker gene using high-field-strength MRI.

STRADalpha deficiency results in aberrant mTORC1 signaling during corticogenesis in humans and mice

Polyhydramnios, megalencephaly, and symptomatic epilepsy syndrome (PMSE) is a rare human autosomal-recessive disorder characterized by abnormal brain development, cognitive disability, and intractable epilepsy. It is caused by homozygous deletions of STE20-related kinase adaptor alpha (STRADA). The underlying pathogenic mechanisms of PMSE and the role of STRADA in cortical development remain unknown. Here, we found that a human PMSE brain exhibits cytomegaly, neuronal heterotopia, and aberrant activation of mammalian target of rapamycin complex 1 (mTORC1) signaling. STRADalpha normally binds and exports the protein kinase LKB1 out of the nucleus, leading to suppression of the mTORC1 pathway. We found that neurons in human PMSE cortex exhibited abnormal nuclear localization of LKB1. To investigate this further, we modeled PMSE in mouse neural progenitor cells (mNPCs) in vitro and in developing mouse cortex in vivo by knocking down STRADalpha expression. STRADalpha-deficient mNPCs were cytomegalic and showed aberrant rapamycin-dependent activation of mTORC1 in association with abnormal nuclear localization of LKB1. Consistent with the observations in human PMSE brain, knockdown of STRADalpha in vivo resulted in cortical malformation, enhanced mTORC1 activation, and abnormal nuclear localization of LKB1. Thus, we suggest that the aberrant nuclear accumulation of LKB1 caused by STRADalpha deficiency contributes to hyperactivation of mTORC1 signaling and disruption of neuronal lamination during corticogenesis, and thereby the neurological features associated with PMSE.

The influence of ferucarbotran on the chondrogenesis of human mesenchymal stem cells

For in vivo applications of magnetically labeled stem cells, biological effects of the labeling procedure have to be precluded. This study evaluates the effect of different ferucarbotran cell labeling protocols on chondrogenic differentiation of human mesenchymal stem cells (hMSC) as well as their implications for MR imaging. hMSC were labeled with ferucarbotran using various protocols: cells were labeled with 100 microg Fe/ml for 4 and 18 h and additional samples were cultured for 6 or 12 days after the 18 h labeling. Supplementary samples were labeled by transfection with protamine sulfate. Iron uptake was quantified by ICP-spectrometry and labeled cells were investigated by transmission electron microscopy and by immunostaining for ferucarbotran. The differentiation potential of labeled cells was compared with unlabeled controls by staining with Alcian blue and Hematoxylin and Eosin, then quantified by measurements of glucosaminoglycans (GAG). Contrast agent effect at 3 T was investigated on days 1 and 14 of chondrogenic differentiation by measuring signal-to-noise ratios on T(2)-SE and T(2)*-GE sequences. Iron uptake was significant for all labeling protocols (p < 0.05). The uptake was highest after transfection with protamine sulfate (25.65 +/- 3.96 pg/cell) and lowest at an incubation time of 4 h without transfection (3.21 +/- 0.21 pg/cell). While chondrogenic differentiation was decreased using all labeling protocols, the decrease in GAG synthesis was not significant after labeling for 4 h without transfection. After labeling by simple incubation, chondrogenesis was found to be dose-dependent. MR imaging showed markedly lower SNR values of all labeled cells compared with the unlabeled controls. This contrast agent effect persisted for 14 days and the duration of differentiation. Magnetic labeling of hMSC with ferucarbotran inhibits chondrogenesis in a dose-dependent manner when using simple incubation techniques. When decreasing the incubation time to 4 h, inhibition of chondrogenesis was not significant.

Magnetoliposomes: versatile innovative nanocolloids for use in biotechnology and biomedicine

The high biocompatibility and versatile nature of liposomes have made these particles keystone components in many hot-topic biomedical research areas. Liposomes can be combined with a large variety of nanomaterials, such as superparamagnetic iron oxide nanocores. Because the unique features of both the magnetizable colloid and the versatile lipid bilayer can be joined, the resulting so-called magnetoliposomes can be exploited in a great array of biotechnological and biomedical applications. In this article, we highlight the use of magnetoliposomes in immobilizing enzymes, both water-soluble and hydrophobic ones, as well as their potential in several biomedical applications, including MRI, hyperthermia cancer treatment and drug delivery. The goal of this article is not to list all known uses of magnetoliposomes but rather to present some conspicuous applications in comparison to other currently used nanoparticles.

Transplantation and magnetic resonance imaging of canine neural progenitor cell grafts in the postnatal dog brain

Cellular transplantation in the form of bone marrow has been one of the primary treatments of many lysosomal storage diseases (LSDs). Although bone marrow transplantation can help central nervous system manifestations in some cases, it has little impact in many LSD patients. Canine models of neurogenetic LSDs provide the opportunity for modeling central nervous system transplantation strategies in brains that more closely approximate the size and architectural complexity of the brains of children. Canine olfactory bulb-derived neural progenitor cells (NPCs) isolated from dog brains were expanded ex vivo and implanted into the caudate nucleus/thalamus or cortex of allogeneic dogs. Canine olfactory bulb-derived NPCs labeled with micron-sized superparamagnetic iron oxide particles were detected by magnetic resonance imaging both in vivo and postmortem. Grafts expressed markers of NPCs (i.e. nestin and glial fibrillary acidic protein), but not the neuronal markers Map2ab or beta-tubulin III. The NPCs were from dogs with the LSD mucopolysaccharidosis VII, which is caused by a deficiency of beta-glucuronidase. When mucopolysaccharidosis VII canine olfactory bulb-NPCs that were genetically corrected with a lentivirus vector ex vivo were transplanted into mucopolysaccharidosis VII recipient brains, they were detected histologically by beta-glucuronidase expression in areas identified by antemortem magnetic resonance imaging tracking. These results demonstrate the potential for ex vivo stem cell-based gene therapy and noninvasive tracking of therapeutic grafts in vivo.

Magnetic resonance imaging detects differences in migration between primary and immortalized neural stem cells

RATIONALE AND OBJECTIVES

The study was performed to evaluate the effect of magnetic resonance imaging (MRI) contrast agent (super paramagnetic iron oxide [SPIO]) on differentiation and migration of primary murine neural stem cells (NSCs) in comparison to a neural stem cell line (C17.2). Because detection of labeled cells depends on the concentration of SPIO particles per imaging voxel, the study was performed at various concentrations of SPIO particles to determine the concentration that could be used for in vivo detection of small clusters of grafted cells.

MATERIALS AND METHODS

Murine primary NSCs or C17.2 cells were labeled with different concentrations of SPIO particles (0, 25, 100, and 250 microg Fe/mL) and in vitro assays were performed to assess cell differentiation. In vivo MRI was performed 7 weeks after neonatal transplantation of labeled cells to evaluate the difference in migration capability of the two cell populations.

RESULTS

Both the primary NSCs and the C17.2 cells differentiated to similar number of neurons (Map2ab-positive cells). Similar patterns of engraftment of C17.2 cells were seen in transplanted mice regardless of the SPIO concentration used. In vivo MRI detection of grafted primary and C17.2 cells was only possible when cells were incubated with 100 microg/mL or higher concentration of SPIO. Extensive migration of C17.2 cells throughout the brain was observed, whereas the migration of the primary NSCs was more restricted.

CONCLUSIONS

Engraftment of primary NSCs can be detected noninvasively by in vivo MRI, and the presence of SPIO particles do not affect the viability, differentiation, or engraftment pattern of the donor cells.

The new challenge of stem cell: brain tumour therapy

The surprising similarity of much brain tumour behavior to the intrinsic properties of the neural stem/progenitor cell has triggered a recent interest in both arming stem cells to track and help eradicate tumours and in viewing stem cell biology as somehow integral to the emergence and/or production of the neoplasm itself. Moreover, based on the unique capacity of neural stem cells (NSCs) to migrate throughout the brain and to target invading tumour cells, the transplantation of NSCs offers a new potential therapeutic approach as a cell-based delivery system for gene therapy in brain tumours. On the one hand, both stem cells and cancer cells are thought to be capable of unlimited proliferation. While on the other, many tumours and cancer cell lines express stem cell markers, suggesting either that cancer cells resemble stem cells or that cancers contain stem-like cells. In this review we highlight the close relationship between normal neural stem cells and brain tumour stem cells and also suggest the possible clinical implications that these similarities could offer.

Efficient in vitro labeling of human neural precursor cells with superparamagnetic iron oxide particles: relevance for in vivo cell tracking

Recent studies have raised appealing possibilities of replacing damaged or lost neural cells by transplanting in vitro-expanded neural precursor cells (NPCs) and/or their progeny. Magnetic resonance (MR) tracking of superparamagnetic iron oxide (SPIO)-labeled cells is a noninvasive technique to track transplanted cells in longitudinal studies on living animals. Murine NPCs and human mesenchymal or hematopoietic stem cells can be efficiently labeled by SPIOs. However, the validation of SPIO-based protocols to label human neural precursor cells (hNPCs) has not been extensively addressed. Here, we report the development and validation of optimized protocols using two SPIOs (Sinerem and Endorem) to label human hNPCs that display bona fide stem cell features in vitro. A careful titration of both SPIOs was required to set the conditions resulting in efficient cell labeling without impairment of cell survival, proliferation, self-renewal, and multipotency. In vivo magnetic resonance imaging (MRI) combined with histology and confocal microscopy indicated that low numbers (5 x 10(3) to 1 x 10(4)) of viable SPIO-labeled hNPCs could be efficiently detected in the short term after transplantation in the adult murine brain and could be tracked for at least 1 month in longitudinal studies. By using this approach, we also clarified the impact of donor cell death to the MR signal. This study describes a simple protocol to label NPCs of human origin using SPIOs at optimized low dosages and demonstrates the feasibility of noninvasive imaging of labeled cells after transplantation in the brain; it also evidentiates potential limitations of the technique that have to be considered, particularly in the perspective of neural cell-based clinical applications.

Applicability and limitations of MR tracking of neural stem cells with asymmetric cell division and rapid turnover: the case of the shiverer dysmyelinated mouse brain

LacZ-transfected C17.2 neural stem cells (NSCs) were labeled with the superparamagnetic iron oxide formulation Feridex prior to ICV injection in shi/shi neonates. Feridex labeling did not alter cell differentiation in vitro and in vivo. Initially, MR images obtained at 11.7T correlated closely to NSC distribution as assessed with anti-dextran and anti-beta-galactosidase double-fluorescent immunostaining. However, at 6 days postgrafting there was already a pronounced mismatch between the hypointense MR signal and the histologically determined cell distribution, with a surprisingly sharp cutoff rather than a gradual decrease of signal. Positive in vivo BrdU labeling of NSCs showed that significant cell replication occurred post-transplantation, causing rapid dilution of Feridex particles between mother and daughter cells toward undetectable levels. Neural differentiation experiments demonstrated asymmetric cell division, explaining the observed sharp cutoff. At later time points (2 weeks), the mismatch further increased by the presence of non-cell-associated Feridex particles resulting from active excretion or cell death. These results are a first demonstration of the inability of MRI to track rapidly dividing and self-renewing, asymmetrically dividing SCs. Therefore, MR cell tracking should only be applied for nonproliferating cells or short-term monitoring of highly-proliferative cells, with mitotic symmetry or asymmetry being important for determining its applicability.

Magnetic resonance imaging as a tool for monitoring stem cell migration

Noninvasive monitoring of stem cells is an important step in developing stem-cell-based therapies. Among several imaging techniques available, magnetic resonance imaging (MRI) provides an effective way to detect implanted stem cells in live animals. In this mini-review, we discuss the available MRI contrast agents and different cell-labeling strategies used for detection of stem cell migration in the brain. The potential effects of MRI contrast agents on stem cell viability and differentiation are also discussed.

ABC transporters, neural stem cells and neurogenesis – a different perspective

Stem cells intrigue. They have the ability to divide exponentially, recreate the stem cell compartment, as well as create differentiated cells to generate tissues. Therefore, they should be natural candidates to provide a renewable source of cells for transplantation applied in regenerative medicine. Stem cells have the capacity to generate specific tissues or even whole organs like the blood, heart, or bones. A subgroup of stem cells, the neural stem cells (NSCs), is characterized as a self-renewing population that generates neurons and glia of the developing brain. They can be isolated, genetically manipulated and differentiated in vitro and reintroduced into a developing, adult or a pathologically altered central nervous system. NSCs have been considered for use in cell replacement therapies in various neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. Characterization of genes with tightly controlled expression patterns during differentiation represents an approach to understanding the regulation of stem cell commitment. The regulation of stem cell biology by the ATP-binding cassette (ABC) transporters has emerged as an important new field of investigation. As a major focus of stem cell research is in the manipulation of cells to enable differentiation into a targeted cell population; in this review, we discuss recent literatures on ABC transporters and stem cells, and propose an integrated view on the role of the ABC transporters, especially ABCA2, ABCA3, ABCB1 and ABCG2, in NSCs' proliferation, differentiation and regulation, along with comparisons to that in hematopoietic and other stem cells.