Imaging of stem cell recruitment to ischemic infarcts in a murine model

Real-time fiber-optic recording of acute-ischemic-stroke signatures

We present an experimental framework and methodology for in vivo studies on rat stroke models that enable a real-time fiber-optic recording of stroke-induced hydrogen peroxide and pH transients in ischemia-affected brain areas. Arrays of reconnectable implantable fiber probes combined with advanced optogenetic fluorescent protein sensors are shown to enable a quantitative multisite time-resolved study of oxidative-stress and acidosis buildup dynamics as the key markers, correlates and possible drivers of ischemic stroke. The fiber probes designed for this work provide a wavelength-multiplex forward-propagation channel for a spatially localized, dual-pathway excitation of genetically encoded fluorescence-protein sensors along with a back-propagation channel for the fluorescence return from optically driven fluorescence sensors. We show that the spectral analysis of the fiber-probe-collected fluorescence return provides means for a high-fidelity autofluorescence background subtraction, thus enhancing the sensitivity of real-time detection of stroke-induced transients and significantly reducing measurement uncertainties in in vivo acute-stroke studies as inherently statistical experiments operating with outcomes of multiply repeated measurements on large populations of individually variable animal stroke models.

Role of hyperpolarization-activated cyclic nucleotide-gated channel HCN2 in embryonic neural stem cell proliferation and differentiation

Hyperpolarization-activated cyclic nucleotide-gated channels (HCN channels) are involved in spontaneous activity in many electrically active cell types such as cardiomyocytes and neurons. In this study, the role of HCN channels in proliferation and migration of Nestin and Sox2 expressing embryonic neural progenitor cells (NPC) originating from the subventricular zone (SVZ) was examined. Immunostaining and PCR data showed that the HCN2 subtype was highly expressed in these cells. Patch clamp recordings revealed a hyperpolarization-activated current, which was sensitive to inhibitors of HCN channels. Using the fluorescence dye bis-(1,3-dibutylbarbituric acid)-trimethineoxonol (DiBAC(4)(3)) we found that a prompt reduction of the extracellular K⁺ concentration, or exposing the cells to acute hypoxia, induced an instant hyperpolarization in the whole cell population. Recovery from low K⁺ induced hyperpolarization after extracellular calcium removal, or by re-oxygenation of hypoxic cells, was sensitive to ZD7288, a HCN channel inhibitor. Treatment of neurosphere cultures from the SVZ with ZD7288 caused a significant and reversible inhibition of neurosphere formation from single cells indicating that proliferation of progenitor cells was reduced. Furthermore, the migration of neuronal cells from neurospheres was considerably retarded in the presence of ZD7288. The results suggest that HCN2 channels are involved in controlling the proliferation of NPC and that HCN2 channel-induced spontaneous electrical activity may trigger the motility response of neurosphere-derived neurons in concert with other ion channels. Furthermore, the response to hypoxia suggests that HCN2 channels may trigger the chemotactic response of NPC to ischemic brain regions seen in many studies.

An antibacterial coated polymer prevents biofilm formation and implant-associated infection

To prevent infections associated with medical implants, various antimicrobial silver-coated implant materials have been developed. However, these materials do not always provide consistent antibacterial effects in vivo despite having dramatic antibacterial effects in vitro, probably because the antibacterial effects involve silver-ion-mediated reactive oxygen species generation. Additionally, the silver application process often requires extremely high temperatures, which damage non-metal implant materials. We recently developed a bacteria-resistant coating consisting of hydroxyapatite film on which ionic silver is immobilized via inositol hexaphosphate chelation, using a series of immersion and drying steps performed at low heat. Here we applied this coating to a polymer, polyetheretherketone (PEEK), and analyzed the properties and antibacterial activity of the coated polymer in vitro and in vivo. The ionic silver coating demonstrated significant bactericidal activity and prevented bacterial biofilm formation in vitro. Bio-imaging of a soft tissue infection mouse model in which a silver-coated PEEK plate was implanted revealed a dramatic absence of bacterial signals 10 days after inoculation. These animals also showed a strong reduction in histological features of infection, compared to the control animals. This innovative coating can be applied to complex structures for clinical use, and could prevent infections associated with a variety of plastic implants.

Illuminating the Regenerative Properties of Stem Cells In Vivo with Bioluminescence Imaging

Preclinical animal studies are essential to the development of safe and effective stem cell therapies. Bioluminescence imaging (BLI) is a powerful tool in animal studies that enables the real-time longitudinal monitoring of stem cells in vivo to elucidate their regenerative properties. This review describes the application of BLI in preclinical stem cell research to address critical challenges in producing successful stem cell therapeutics. These challenges include stem cell survival, proliferation, homing, stress response, and differentiation. The applications presented here utilize bioluminescence to investigate a variety of stem and progenitor cells in several different in vivo models of disease and implantation. An overview of luciferase reporters is provided, along with the advantages and disadvantages of BLI. Additionally, BLI is compared to other preclinical imaging modalities and potential future applications of this technology are discussed in emerging areas of stem cell research.

Neural stem cell therapy of foetal onset hydrocephalus using the HTx rat as experimental model

Foetal onset hydrocephalus is a disease starting early in embryonic life; in many cases it results from a cell junction pathology of neural stem (NSC) and neural progenitor (NPC) cells forming the ventricular zone (VZ) and sub-ventricular zone (SVZ) of the developing brain. This pathology results in disassembling of VZ and loss of NSC/NPC, a phenomenon known as VZ disruption. At the cerebral aqueduct, VZ disruption triggers hydrocephalus while in the telencephalon, it results in abnormal neurogenesis. This may explain why derivative surgery does not cure hydrocephalus. NSC grafting appears as a therapeutic opportunity. The present investigation was designed to find out whether this is a likely possibility. HTx rats develop hereditary hydrocephalus; 30-40% of newborns are hydrocephalic (hyHTx) while their littermates are not (nHTx). NSC/NPC from the VZ/SVZ of nHTx rats were cultured into neurospheres that were then grafted into a lateral ventricle of 1-, 2- or 7-day-old hyHTx. Once in the cerebrospinal fluid, neurospheres disassembled and the freed NSC homed at the areas of VZ disruption. A population of homed cells generated new multiciliated ependyma at the sites where the ependyma was missing due to the inherited pathology. Another population of NSC homed at the disrupted VZ differentiated into βIII-tubulin+ spherical cells likely corresponding to neuroblasts that progressed into the parenchyma. The final fate of these cells could not be established due to the protocol used to label the grafted cells. The functional outcomes of NSC grafting in hydrocephalus remain open. The present study establishes an experimental paradigm of NSC/NPC therapy of foetal onset hydrocephalus, at the etiologic level that needs to be further explored with more analytical methodologies.

Dual-Modal Imaging-Guided Precise Tracking of Bioorthogonally Labeled Mesenchymal Stem Cells in Mouse Brain Stroke

Noninvasive and precise stem cell tracking after transplantation in living subject is very important to monitor both stem cell destinations and their in vivo fate, which is closely related to their therapeutic efficacy. Herein, we developed bicyclo[6.1.0]nonyne (BCN)-conjugated glycol chitosan nanoparticles (BCN-NPs) as a delivery system of dual-modal stem cell imaging probes. Near-infrared fluorescent (NIRF) dye Cy5.5 was chemically conjugated to the BCN-NPs, and then oleic acid-coated superparamagnetic iron oxide nanoparticles (OA-Fe₃O₄ NPs) were encapsulated into BCN-NPs, resulting in Cy5.5-labeled and OA-Fe₃O₄ NP-encapsulated BCN-NPs (BCN-dual-NPs). For bioorthogonal labeling of human adipose-derived mesenchymal stem cells (hMSCs), first, hMSCs were treated with tetra-acetylated N-azidoacetyl-d-mannosamine (Ac₄ManNAz) for generating azide (-N₃) groups onto their surface via metabolic glycoengineering. Second, azide groups on the cell surface were successfully chemically labeled with BCN-dual-NPs via bioorthogonal click chemistry in vitro. This bioorthogonal labeling of hMSCs could greatly increase the cell labeling efficiency, safety, and imaging sensitivity, compared to only nanoparticle-derived labeling technology. The dual-modal imaging-guided precise tracking of bioorthogonally labeled hMSCs was tested in the photothrombotic stroke mouse model via intraparenchymal injection. Finally, BCN-dual-NPs-labeled hMSCs could be effectively tracked by their migration from the implanted site to the brain stroke lesion using NIRF/T₂-weighted magnetic resonance (MR) dual-modal imaging for 14 days. Our observation would provide a potential application of bioorthogonally labeled stem cell imaging in regenerative medicine by providing safety and high labeling efficiency in vitro and in vivo.

Quantitative in vivo dual-color bioluminescence imaging in the mouse brain

Bioluminescence imaging (BLI) is an optical imaging method that can be translated from the cell culture dish in vitro to cell tracking in small animal models in vivo. In contrast to the more widely used fluorescence imaging, which requires light excitation, in BLI the light is exclusively generated by the enzyme luciferase. The luciferase gene can be engineered to target and monitor almost every cell and biological process quantitatively in vitro and even from deep tissue in vivo. While initially used for tumor imaging, bioluminescence was recently optimized for mouse brain imaging of neural cells and monitoring of viability or differentiation of grafted stem cells. Here, we describe the use of bright color-shifted firefly luciferases (Flucs) based on the thermostable x5 Fluc that emit red and green for effective and quantitative unmixing of two human cell populations in vitro and after transplantation into the mouse brain in vivo. Spectral unmixing predicts the ratio of luciferases in vitro and a mixture of cells precisely for cortical grafts, however, with less accuracy for striatal grafts. This dual-color approach enables the simultaneous visualization and quantification of two cell populations on the whole brain scale, with particular relevance for translational studies of neurological disorders providing information on stem cell survival and differentiation in one imaging session in vivo.

Neurospheres from neural stem/neural progenitor cells (NSPCs) of non-hydrocephalic HTx rats produce neurons, astrocytes and multiciliated ependyma: the cerebrospinal fluid of normal and hydrocephalic rats supports such a differentiation

Fetal onset hydrocephalus and abnormal neurogenesis are two inseparable phenomena turned on by a cell junction pathology first affecting neural stem/progenitor cells (NSPCs) and later the multiciliated ependyma. The neurological impairment of children born with hydrocephalus is not reverted by derivative surgery. NSPCs and neurosphere (NE) grafting into the cerebrospinal fluid (CSF) of hydrocephalic fetuses thus appears as a promising therapeutic procedure. There is little information about the cell lineages actually forming the NE as they grow throughout their days in vitro (DIV). Furthermore, there is no information on how good a host the CSF is for grafted NE. Here, we use the HTx rat, a model with hereditary hydrocephalus, with the mutation expressed in about 30% of the litter (hyHTx), while the littermates develop normally (nHTx). The investigation was designed (i) to establish the nature of the cells forming 4 and 6-DIV NE grown from NSPCs collected from PN1/nHTx rats and (ii) to study the effects on these NEs of CSF collected from nHTx and hyHTx. Immunofluorescence analyses showed that 90% of cells forming 4-DIV NEs were non-committed multipotential NSPCs, while in 6-DIV NE, 40% of the NSPCs were already committed into neuronal, glial and ependymal lineages. Six-DIV NE further cultured for 3 weeks in the presence of fetal bovine serum, CSF from nHTx or CSF from hyHTx, differentiated into neurons, astrocytes and βIV-tubulin+ multiciliated ependymal cells that were joined together by adherent junctions and displayed synchronized cilia beating. This supports the possibility that ependymal cells are born from subpopulations of NSC with their own time table of differentiation. As a whole, the findings indicate that the CSF is a supportive medium to host NE and that NE grafted into the CSF have the potential to produce neurons, glia and ependyma.

In vivo imaging biomarkers of neuroinflammation in the development and assessment of stroke therapies - towards clinical translation

Modulation of the inflammatory microenvironment after stroke opens a new avenue for the development of novel neurorestorative therapies in stroke. Understanding the spatio-temporal profile of (neuro-)inflammatory imaging biomarkers in detail thereby represents a crucial factor in the development and application of immunomodulatory therapies. The early integration of quantitative molecular imaging biomarkers in stroke drug development may provide key information about (i) early diagnosis and follow-up, (ii) spatio-temporal drug-target engagement (pharmacodynamic biomarker), (iii) differentiation of responders and non-responders in the patient cohort (inclusion/exclusion criteria; predictive biomarkers), and (iv) the mechanism of action. The use of targeted imaging biomarkers for may thus allow clinicians to decipher the profile of patient-specific inflammatory activity and the development of patient-tailored strategies for immunomodulatory and neuro-restorative therapies in stroke. Here, we highlight the recent developments in preclinical and clinical molecular imaging biomarkers of neuroinflammation (endothelial markers, microglia, MMPs, cell labeling, future developments) in stroke and outline how imaging biomarkers can be used in overcoming current translational roadblocks and attrition in order to advance new immunomodulatory compounds within the clinical pipeline.

Grafted Neural Stem Cells Show Lesion-Specific Migration in Radiation-Injured Rat Brains

Neural stem cells (NSCs) exhibit preferential homing toward some types of brain lesion, but their migratory property during radiation brain injury (RBI) remains unexplored. Here, we use the superparamagnetic iron oxide (SPIO)-labeled magnetic resonance imaging (MRI) technology to determine the migration of transplanted NSCs in two partial RBI models in real time, created by administering 30–55 Gy of radiation to the right or posterior half of the adult rat brain. SPIO-labeled NSCs were stereotactically grafted into the uninjured side one week after RBI. The migration of SPIO-labeled NSCs in live radiation-injured brains was traced by MRI for up to 28 days after engraftment and quantified for their moving distances and speeds. A high labeling efficiency (>90%) was achieved by incubating NSCs with 100 μg ml⁻¹ of SPIO for 12–24 hours. Upon stereotactic transplantation into the healthy side of the brain, SPIO-labeled NSCs were distinctively detected as hypointense signals on T2-weighted images (T2WI), showed sustained survival for up to 4 weeks, and exhibited directional migration to the radiation-injured side of the brain with a speed of 86–127 μm per day. The moving kinetics of grafted NSCs displayed no difference in brains receiving a high (55 Gy) vs. moderate (45 Gy) dose of radiation, but was slower in the right RBI model than in the posterior RBI model. This study shows that NSCs can be effectively labeled by SPIO and traced in vivo by MRI, and that grafted NSCs exhibit directional migration toward RBI sites in a route-dependent but radiation dose-independent manner.

Neural stem cells (NSCs) exhibit preferential homing toward some types of brain lesion, but their migratory property during radiation brain injury (RBI) remains unexplored.

Delayed Propionibacterium acnes surgical site infections occur only in the presence of an implant

Whether Propionibacterium acnes (P. acnes) causes surgical-site infections (SSI) after orthopedic surgery is controversial. We previously reported that we frequently find P. acnes in intraoperative specimens, yet none of the patients have clinically apparent infections. Here, we tracked P. acnes for 6 months in a mouse osteomyelitis model. We inoculated P. acnes with an implant into the mouse femur in the implant group; the control group was treated with the bacteria but no implant. We then observed over a 6-month period using optical imaging system. During the first 2 weeks, bacterial signals were detected in the femur in the both groups. The bacterial signal completely disappeared in the control group within 28 days. Interestingly, in the implant group, bacterial signals were still present 6 months after inoculation. Histological and scanning electron-microscope analyses confirmed that P. acnes was absent from the control group 6 months after inoculation, but in the implant group, the bacteria had survived in a biofilm around the implant. PCR analysis also identified P. acnes in the purulent effusion from the infected femurs in the implant group. To our knowledge, this is the first report showing that P. acnes causes SSI only in the presence of an implant.

Hes1 inhibitor isolated by target protein oriented natural products isolation (TPO-NAPI) of differentiation activators of neural stem cells

Hes1 dimer inhibitor, agalloside (2), which can accelerate the differentiation of neural stem cells was isolated by using Hes1-immobilized beads.

The Hes1 dimer inhibitor, agalloside (2), which can accelerate the differentiation of neural stem cells is described. Six natural products, including one new natural product, which bind to Hes1 were rapidly isolated by a developed “target protein oriented natural products isolation” (TPO-NAPI) method using Hes1-immobilized beads. Of the six compounds, 2 inhibited Hes1 dimer formation at both the protein- and cellular level. Neural stem cells treated with 2 differentiated to neurons with longer neurites than cells treated with varproic acid or retinoic acid. Moreover, 2 exhibited specificity for neurons. This promotion of differentiation was supported by an increase in the mRNA expression of the proneural genes, Mash1 and Ngn2, which were inhibited by Hes1.

Cell tracking technologies for acute ischemic brain injury

Stem cell therapy has showed considerable potential in the treatment of stroke over the last decade. In order that these therapies may be optimized, the relative benefits of growth factor release, immunomodulation, and direct tissue replacement by therapeutic stem cells are widely under investigation. Fundamental to the progress of this research are effective imaging techniques that enable cell tracking in vivo. Direct analysis of the benefit of cell therapy includes the study of cell migration, localization, division and/or differentiation, and survival. This review explores the various imaging tools currently used in clinics and laboratories, addressing image resolution, long-term cell monitoring, imaging agents/isotopes, as well as safety and costs associated with each technique. Finally, burgeoning tracking techniques are discussed, with emphasis on multimodal imaging.

Inubosins A, B, and C are acridine alkaloids isolated from a culture of Streptomyces sp. IFM 11440 with Ngn2 promoter activity

Three new acridine alkaloids, inubosins A (1), B (2), and C (3), were isolated from an extract of a culture of Streptomyces sp. IFM 11440 using bioassay-guided fractionation. Neurogenin2 (Ngn2) is an activator-type basic helix-loop-helix transcription factor that promotes neural stem cell differentiation. Using cell-based Ngn2 promoter activity-guided screening, Streptomyces sp. IFM 11440 was found to induce Ngn2 promoter activity. The structures of 1-3 were established using spectroscopic methods, including 1D- and 2D-NMR measurements. Inubosin B (2) showed potent Ngn2 promoter activity. Moreover, inubosin B (2) increased mRNA expression of genes related to neural stem cell differentiation.

In vivo imaging of endogenous neural stem cells in the adult brain

The discovery of endogenous neural stem cells (eNSCs) in the adult mammalian brain with their ability to self-renew and differentiate into functional neurons, astrocytes and oligodendrocytes has raised the hope for novel therapies of neurological diseases. Experimentally, those eNSCs can be mobilized in vivo, enhancing regeneration and accelerating functional recovery after, e.g., focal cerebral ischemia, thus constituting a most promising approach in stem cell research. In order to translate those current experimental approaches into a clinical setting in the future, non-invasive imaging methods are required to monitor eNSC activation in a longitudinal and intra-individual manner. As yet, imaging protocols to assess eNSC mobilization non-invasively in the live brain remain scarce, but considerable progress has been made in this field in recent years. This review summarizes and discusses the current imaging modalities suitable to monitor eNSCs in individual experimental animals over time, including optical imaging, magnetic resonance tomography and-spectroscopy, as well as positron emission tomography (PET). Special emphasis is put on the potential of each imaging method for a possible clinical translation, and on the specificity of the signal obtained. PET-imaging with the radiotracer 3’-deoxy-3’-[¹⁸F]fluoro-L-thymidine in particular constitutes a modality with excellent potential for clinical translation but low specificity; however, concomitant imaging of neuroinflammation is feasible and increases its specificity. The non-invasive imaging strategies presented here allow for the exploitation of novel treatment strategies based upon the regenerative potential of eNSCs, and will help to facilitate a translation into the clinical setting.

Stem cell imaging: from bench to bedside

Although cellular therapies hold great promise for the treatment of human disease, results from several initial clinical trials have not shown a level of efficacy required for their use as a first line therapy. Here we discuss how in vivo molecular imaging has helped identify barriers to clinical translation and potential strategies that may contribute to successful transplantation and improved outcomes, with a focus on cardiovascular and neurological diseases. We conclude with a perspective on the future role of molecular imaging in defining safety and efficacy for clinical implementation of stem cell therapies.

A novel mouse model of soft-tissue infection using bioluminescence imaging allows noninvasive, real-time monitoring of bacterial growth

Musculoskeletal infections, including surgical-site and implant-associated infections, often cause progressive inflammation and destroy areas of the soft tissue. Treating infections, especially those caused by multi-antibiotic resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) remains a challenge. Although there are a few animal models that enable the quantitative evaluation of infection in soft tissues, these models are not always reproducible or sustainable. Here, we successfully established a real-time, in vivo, quantitative mouse model of soft-tissue infection in the superficial gluteus muscle (SGM) using bioluminescence imaging. A bioluminescent strain of MRSA was inoculated into the SGM of BALB/c adult male mice, followed by sequential measurement of bacterial photon intensity and serological and histological analyses of the mice. The mean photon intensity in the mice peaked immediately after inoculation and remained stable until day 28. The serum levels of interleukin-6, interleukin-1 and C-reactive protein at 12 hours after inoculation were significantly higher than those prior to inoculation, and the C-reactive protein remained significantly elevated until day 21. Histological analyses showed marked neutrophil infiltration and abscesses containing necrotic and fibrous tissues in the SGM. With this SGM mouse model, we successfully visualized and quantified stable bacterial growth over an extended period of time with bioluminescence imaging, which allowed us to monitor the process of infection without euthanizing the experimental animals. This model is applicable to in vivo evaluations of the long-term efficacy of novel antibiotics or antibacterial implants.

Evaluating reporter genes of different luciferases for optimized in vivo bioluminescence imaging of transplanted neural stem cells in the brain

Bioluminescence imaging (BLI) has become the method of choice for optical tracking of cells in small laboratory animals. However, the use of luciferases from different species, depending on different substrates and emitting at distinct wavelengths, has not been optimized for sensitive neuroimaging. In order to identify the most suitable luciferase, this quantitative study compared the luciferases Luc2, CBG99, PpyRE9 and hRluc. Human embryonic kidney (HEK-293) cells and mouse neural stem cells were transduced by lentiviral vector-mediated transfer to express one of the four luciferases, together with copGFP. A T2A peptide linker promoted stoichiometric expression between both imaging reporters and the comparison of cell populations upon flow cytometry. Cell dilution series were used to determine highest BLI sensitivity in vitro for Luc2. However, Coelenterazine h-dependent hRluc signals clearly exceeded d-luciferin-dependent BLI in vitro. For the quantitative in vivo analysis, cells were transplanted into mouse brain and BLI was performed including the recording of emission kinetics and spectral characteristics. Differences in light kinetics were observed for d-luciferin vs Coelenterazine h. The emission spectra of Luc2 and PpyRE9 remained almost unchanged, while the emission spectrum of CBG99 became biphasic. Most importantly, photon emission decreased in the order of Luc2, CBG99, PpyRE9 to hRluc. The feasibility of combining different luciferases for dual color and dual substrate neuroimaging was tested and discussed. This investigation provides the first complete quantitative comparison of different luciferases expressed by neural stem cells. It results in a clear recommendation of Luc2 as the best luciferase selection for in vivo neuroimaging.

A review of novel optical imaging strategies of the stroke pathology and stem cell therapy in stroke

Transplanted stem cells can induce and enhance functional recovery in experimental stroke. Invasive analysis has been extensively used to provide detailed cellular and molecular characterization of the stroke pathology and engrafted stem cells. But post mortem analysis is not appropriate to reveal the time scale of the dynamic interplay between the cell graft, the ischemic lesion and the endogenous repair mechanisms. This review describes non-invasive imaging techniques which have been developed to provide complementary in vivo information. Recent advances were made in analyzing simultaneously different aspects of the cell graft (e.g., number of cells, viability state, and cell fate), the ischemic lesion (e.g., blood-brain-barrier consistency, hypoxic, and necrotic areas) and the neuronal and vascular network. We focus on optical methods, which permit simple animal preparation, repetitive experimental conditions, relatively medium-cost instrumentation and are performed under mild anesthesia, thus nearly under physiological conditions. A selection of recent examples of optical intrinsic imaging, fluorescence imaging and bioluminescence imaging to characterize the stroke pathology and engrafted stem cells are discussed. Special attention is paid to novel optimal reporter genes/probes for genetic labeling and tracking of stem cells and appropriate transgenic animal models. Requirements, advantages and limitations of these imaging platforms are critically discussed and placed into the context of other non-invasive techniques, e.g., magnetic resonance imaging and positron emission tomography, which can be joined with optical imaging in multimodal approaches.

Fluorescent protein-expressing neural progenitor cells as a tool for transplantation studies

The purpose of this study was to generate quadruple fluorescent protein (QFP) transgenic mice as a source for QFP-expressing neural stem and progenitor cells (NSCs/NPCs) that could be utilized as a tool for transplantation research. When undifferentiated, these NSCs only express cyan fluorescent protein (CFP); however, upon neuronal differentiation, the cells express yellow fluorescent protein (YFP). During astrocytic differentiation, the cells express green fluorescent protein (GFP), and during oligodendrocytic differentiation, the cells express red fluorescent protein (DsRed). Using immunocytochemistry, immunoblotting, flow cytometry and electrophysiology, quadruple transgenic NPCs (Q-NPCs) and GFP-sorted NPCs were comprehensively characterized in vitro. Overall, the various transgenes did not significantly affect proliferation and differentiation of transgenic NPCs in comparison to wild-type NPCs. In contrast to a strong CFP and GFP expression in vitro, NPCs did not express YFP and dsRed either during proliferation or after differentiation in vitro. GFP-positive sorted NPCs, expressing GFP under the control of the human GFAP promoter, demonstrated a significant improvement in astroglial differentiation in comparison to GFP-negative sorted NPCs. In contrast to non-sorted and GFP-positive sorted NPCs, GFP-negative sorted NPCs demonstrated a high proportion of neuronal differentiation and proved to be functional in vitro. At 6 weeks after the intracerebroventricular transplantation of Q-NPCs into neonatal wild-type mice, CFP/DCX (doublecortin) double-positive transplanted cells were observed. The Q-NPCs did not express any other fluorescent proteins and did not mature into neuronal or glial cells. Although this model failed to visualize NPC differentiation in vivo, we determined that activation of the NPC glial fibrillary acid protein (GFAP) promoter, as indicated by GFP expression, can be used to separate neuronal and glial progenitors as a valuable tool for transplantation studies.

White matter tracts for the trafficking of neural progenitor cells characterized by cellular MRI and immunohistology: the role of CXCL12/CXCR4 signaling

White matter tracts are important for the trafficking of neural progenitor cells (NPCs) in both normal and pathological conditions, but the underlying mechanism is not clear. The directionality of white matter is advantageous for molecules or cells to distribute over a long distance, but this feature is unlikely solely responsible for efficient migration. The present study hypothesizes that the efficient migration of NPCs into white matter is under the influences of neurochemical attraction—CXCL12/CXCR4 signaling, a major mechanism underlying the targeted migration of NPCs. To test this view, the present study investigated the effects of CXCL12 administration into the corpus callosum (CC) on the migratory behavior of transplanted NPCs. A living animal tracking platform based on MRI and a magnetic cell labeling technique was employed. The NPCs were magnetically labeled and then transplanted at the right end of the CC. CXCL12 was infused continuously at the left end. Migration of NPCs was monitored repeatedly over a 7-day course using 3D gradient echo T2*-weighted imaging. It was found that, CXCL12 induced NPCs to migrate up to 1,881 μm from the graft whereas the spontaneous migration was mere 200 μm. CXCL12 induced migration that was nine times as efficient in the speed. The results indicate that the CXCL12/CXCR4 signaling may be a mechanism via which NPCs efficiently migrate along the white matter tracts. The study also presents a potential strategy for facilitating the targeted migration in NPC therapy for brain disorders.

Stem cell-based therapies for ischemic stroke

In recent years, stem cell-based approaches have attracted more attention from scientists and clinicians due to their possible therapeutical effect on stroke. Animal studies have demonstrated that the beneficial effects of stem cells including embryonic stem cells (ESCs), inducible pluripotent stem cells (iPSCs), neural stem cells (NSCs), and mesenchymal stem cell (MSCs) might be due to cell replacement, neuroprotection, endogenous neurogenesis, angiogenesis, and modulation on inflammation and immune response. Although several clinical studies have shown the high efficiency and safety of stem cell in stroke management, mainly MSCs, some issues regarding to cell homing, survival, tracking, safety, and optimal cell transplantation protocol, such as cell dose and time window, should be addressed. Undoubtably, stem cell-based gene therapy represents a novel potential therapeutic strategy for stroke in future.

Using C-arm x-ray imaging to guide local reporter probe delivery for tracking stem cell engraftment

Poor cell survival and difficulties with visualization of cell delivery are major problems with current cell transplantation methods. To protect cells from early destruction, microencapsulation methods have been developed. The addition of a contrast agent to the microcapsule also could enable tracking by MR, ultrasound, and X-ray imaging. However, determining the cell viability within the microcapsule still remains an issue. Reporter gene imaging provides a way to determine cell viability, but delivery of the reporter probe by systemic injection may be hindered in ischemic diseases. In the present study, mesenchymal stem cells (MSCs) were transfected with triple fusion reporter gene containing red fluorescent protein, truncated thymidine kinase (SPECT/PET reporter) and firefly luciferase (bioluminescence reporter). Transfected cells were microencapsulated in either unlabeled or perfluorooctylbromide (PFOB) impregnated alginate. The addition of PFOB provided radiopacity to enable visualization of the microcapsules by X-ray imaging. Before intramuscular transplantation in rabbit thigh muscle, the microcapsules were incubated with D-luciferin, and bioluminescence imaging (BLI) was performed immediately. Twenty-four and forty-eight hours post transplantation, c-arm CT was used to target the luciferin to the X-ray-visible microcapsules for BLI cell viability assessment, rather than systemic reporter probe injections. Not only was the bioluminescent signal emission from the PFOB-encapsulated MSCs confirmed as compared to non-encapsulated, naked MSCs, but over 90% of injection sites of PFOB-encapsulated MSCs were visible on c-arm CT. The latter aided in successful targeting of the reporter probe to injection sites using conventional X-ray imaging to determine cell viability at 1-2 days post transplantation. Blind luciferin injections to the approximate location of unlabeled microcapsules resulted in successful BLI signal detection in only 18% of injections. In conclusion, reporter gene probes can be more precisely targeted using c-arm CT for in vivo transplant viability assessment, thereby avoiding large and costly systemic injections of a reporter probe.

Cell based therapies for ischemic stroke: from basic science to bedside

Cell therapy is emerging as a viable therapy to restore neurological function after stroke. Many types of stem/progenitor cells from different sources have been explored for their feasibility and efficacy for the treatment of stroke. Transplanted cells not only have the potential to replace the lost circuitry, but also produce growth and trophic factors, or stimulate the release of such factors from host brain cells, thereby enhancing endogenous brain repair processes. Although stem/progenitor cells have shown a promising role in ischemic stroke in experimental studies as well as initial clinical pilot studies, cellular therapy is still at an early stage in humans. Many critical issues need to be addressed including the therapeutic time window, cell type selection, delivery route, and in vivo monitoring of their migration pattern. This review attempts to provide a comprehensive synopsis of preclinical evidence and clinical experience of various donor cell types, their restorative mechanisms, delivery routes, imaging strategies, future prospects and challenges for translating cell therapies as a neurorestorative regimen in clinical applications.

Contralaterally transplanted human embryonic stem cell-derived neural precursor cells (ENStem-A) migrate and improve brain functions in stroke-damaged rats

The transplantation of neural precursor cells (NPCs) is known to be a promising approach to ameliorating behavioral deficits after stroke in a rodent model of middle cerebral artery occlusion (MCAo). Previous studies have shown that transplanted NPCs migrate toward the infarct region, survive and differentiate into mature neurons to some extent. However, the spatiotemporal dynamics of NPC migration following transplantation into stroke animals have yet to be elucidated. In this study, we investigated the fates of human embryonic stem cell (hESC)-derived NPCs (ENStem-A) for 8 weeks following transplantation into the side contralateral to the infarct region using 7.0T animal magnetic resonance imaging (MRI). T2- and T2*-weighted MRI analyses indicated that the migrating cells were clearly detectable at the infarct boundary zone by 1 week, and the intensity of the MRI signals robustly increased within 4 weeks after transplantation. Afterwards, the signals were slightly increased or unchanged. At 8 weeks, we performed Prussian blue staining and immunohistochemical staining using human-specific markers, and found that high percentages of transplanted cells migrated to the infarct boundary. Most of these cells were CXCR4-positive. We also observed that the migrating cells expressed markers for various stages of neural differentiation, including Nestin, Tuj1, NeuN, TH, DARPP-32 and SV38, indicating that the transplanted cells may partially contribute to the reconstruction of the damaged neural tissues after stroke. Interestingly, we found that the extent of gliosis (glial fibrillary acidic protein-positive cells) and apoptosis (TUNEL-positive cells) were significantly decreased in the cell-transplanted group, suggesting that hESC-NPCs have a positive role in reducing glia scar formation and cell death after stroke. No tumors formed in our study. We also performed various behavioral tests, including rotarod, stepping and modified neurological severity score tests, and found that the transplanted animals exhibited significant improvements in sensorimotor functions during the 8 weeks after transplantation. Taken together, these results strongly suggest that hESC-NPCs have the capacity to migrate to the infarct region, form neural tissues efficiently and contribute to behavioral recovery in a rodent model of ischemic stroke.

Translation of the ecological trap concept to glioma therapy: the cancer cell trap concept

Viewing tumors as ecosystems offers the opportunity to consider how ecological concepts can be translated to novel therapeutic perspectives. The ecological trap concept emerged approximately half a century ago when it was observed that animals can prefer an environment of low quality for survival over other available environments of higher quality. The presence of such a trap can drive a local population to extinction. The cancer cell trap concept is the translation of the ecological trap into glioma therapy. It exploits and diverts the invasive potential of glioma cells by guiding their migration towards specific locations where a local therapy can be delivered efficiently. This illustrates how an ecological concept can change therapeutic obstacles into therapeutic tools.

Evaluation of metabolomic changes as a biomarker of chondrogenic differentiation in 3D-cultured human mesenchymal stem cells using proton (1H) nuclear magnetic resonance spectroscopy

PURPOSE

The purpose of this study was to evaluate the metabolomic changes in 3D-cultured human mesenchymal stem cells (hMSCs) in alginate beads, so as to identify biomarkers during chondrogenesis using (1)H nuclear magnetic resonance (NMR) spectroscopy.

MATERIALS AND METHODS

hMSCs (2×10(6) cells/mL) were seeded into alginate beads, and chondrogenesis was allowed to progress for 15 days. NMR spectra of the chondrogenic hMSCs were obtained at 4, 7, 11, and 15 days using a 14.1-T (600-MHz) NMR with the water suppression sequence, zgpr. Real-Time polymerase chain reaction (PCR) was performed to confirm that that the hMSCs differentiated into chondrocytes and to analyze the metabolomic changes indicated by the NMR spectra.

RESULTS

During chondrogenesis, changes were detected in several metabolomes as hMSC chondrogenesis biomarkers, e.g., fatty acids, alanine, glutamate, and phosphocholine. The metabolomic changes were compared with the Real-Time PCR results, and significant differences were determined using statistical analysis. We found that changes in metabolomes were closely related to biological reactions that occurred during the chondrogenesis of hMSCs.

CONCLUSIONS

In this study, we confirm that metabolomic changes detected by (1)H-NMR spectroscopy during chondrogenic differentiation of 3D-cultured hMSCs in alginate beads can be considered as biomarkers of stem cell differentiation.

Multimodality molecular imaging of stem cells therapy for stroke

Stem cells have been proposed as a promising therapy for treating stroke. While several studies have demonstrated the therapeutic benefits of stem cells, the exact mechanism remains elusive. Molecular imaging provides the possibility of the visual representation of biological processes at the cellular and molecular level. In order to facilitate research efforts to understand the stem cells therapeutic mechanisms, we need to further develop means of monitoring these cells noninvasively, longitudinally and repeatedly. Because of tissue depth and the blood-brain barrier (BBB), in vivo imaging of stem cells therapy for stroke has unique challenges. In this review, we describe existing methods of tracking transplanted stem cells in vivo, including magnetic resonance imaging (MRI), nuclear medicine imaging, and optical imaging (OI). Each of the imaging techniques has advantages and drawbacks. Finally, we describe multimodality imaging strategies as a more comprehensive and potential method to monitor transplanted stem cells for stroke.

Characterization of partial ligation-induced carotid atherosclerosis model using dual-modality molecular imaging in ApoE knock-out mice

Background

Recently, partial ligation of the common carotid artery (CCA) was reported to induce carotid atheromata rapidly in apolipoprotein-E knockout (ApoE^-/-) mice. We investigated this new atherosclerosis model by using combined matrix-metalloproteinase (MMP) near-infrared fluorescent (NIRF) imaging and macrophage-tracking luciferase imaging.

Methodology and Principal Findings

Partial ligation of the left CCA was performed in 10-week-old ApoE^-/- mice on a high fat diet (n=33); the internal and external carotid arteries and occipital artery were ligated, while the superior thyroid artery was left intact. Two thirds of the animals were treated with either LiCl or atorvastatin. At 1-week, Raw264.7 macrophages modified to express the enhanced firefly-luciferase reporter gene (10⁷ Raw-luc cells) were injected intravenously. At 2-week, NIRF molecular imaging visualized strong MMP-2/9 activity in the ligated area of the left CCA as well as in the aortic arch. Left-to-right ratios of the NIRF signal intensities in the CCA had a decreasing gradient from the highest value in the upper-most ligated area to the lowest value in the lower-most region adjacent to the aortic arch. Luciferase imaging showed that most Raw-luc macrophages were recruited to the ligated area of the CCA rather than to the aortic arch, despite similarly strong MMP-2/9-related NIRF signal intensities in both areas. In addition, LiCl or atorvastatin could reduce MMP-2/9 activity in the aortic arch but not in the ligated area of the CCA.

Conclusions/Significance

This is the first molecular imaging study to characterize the partial ligation-induced carotid atherosclerosis model. Molecularly divergent types of atherosclerosis were identified: conventional lipogenic atherosclerosis in the aorta vs. flow-related mechanical atherosclerosis in the partially ligated left system.

Wrapped omentum with periosteum concurrent with adipose derived adult stem cells for bone tissue engineering in dog model

Adipose derived adult stem cells (ASCs) are multipotent cells that are able to differentiate into osteoblasts in presence of certain factors. The histological characteristics of periosteum makes it a specific tissue with a unique capacity to be engineered. Higher flexibility of the greater omentum is useful for reconstructive surgery. These criteria make it suitable for tissue engineering. The present study was designed to evaluate bone tissue engineering with periosteal free graft concurrent with ASCs and pedicle omentum in dog model. Twelve young female indigenous dogs were used in this experiment. In omental group (n = 4), end of omentum was wrapped by periosteum of the radial bone in abdomen of each dog. In omental-autogenously ASCs group (n = 4), 1 ml of ASCs was injected into the wrapped omentum with periosteum while in omental-allogenously ASCs group (n = 4), 1 ml of allogenous ASCs was injected. Lateral view radiographs were taken from the abdominal cavity postoperatively at the 2nd, 4th, 6th and 8th weeks post-surgery. Eight weeks after operation the dogs were re-anesthetized and the wrapped omenum by periosteum in all groups was found and removed for histopathological evaluation. Our results showed that omentum-periosteum, omental-periosteum-autogenous ASCs and omental-periosteum-allogenous ASCs groups demonstrated bone tissue formation in the abdominal cavity in dog model. The radiological, macroscopical and histological findings of the present study by the end of 8 weeks post-surgery indicate bone tissue engineering in all three groups in an equal level. The present study has shown that the wrapped omentum with periosteum concurrent with ASCs (autogenous or allogenous ASCs) lead to a favorable bone tissue formation. We suggested that it may be useful when pedicle graft omentum used concurrent with periosteum in the bone defect reconstruction, and this phenomenon should be studied in future.

High MRI performance fluorescent mesoporous silica-coated magnetic nanoparticles for tracking neural progenitor cells in an ischemic mouse model

Multifunctional probes with high MRI sensitivity and high efficiency for cell labeling are desirable for MR cell imaging. Herein, we have fabricated fluorescent mesoporous silica-coated superparamagnetic iron oxide nanoparticles (fmSiO4@SPIONs) for neural progenitor cell (C17.2) MR imaging. FmSiO4@SPIONs were discrete and uniform in size, and had a clear core-shell structure. The magnetic core size was about 10 nm and the fluorescent mesoporous silica coating layer was around 20 nm. Compared with fluorescent dense silica-coated SPIONs (fdSiO4@SPIONs) with a similar size, fmSiO4@SPIONs demonstrated higher MR sensitivity and cell labeling efficiency. When implanted into the right hemisphere of stroke mice, contralateral to the ischemic territory, a small amount of labeled cells were able to be tracked migrating to the lesion sites using a clinical MRI scanner (3 T). More impressively, even when administered intravenously, the labeled cells could also be monitored homing to the ischemic area. MRI observations were corroborated by histological studies of the brain tissues. Our study demonstrated that fmSiO4@SPIONs are highly effective for cell imaging and hold great promise for MRI cell tracking in future.

Noninvasive multimodal imaging of stem cell transplants in the brain using bioluminescence imaging and magnetic resonance imaging

Transplantation of stem cells represents a promising approach for the therapy of different brain diseases, including stroke, Parkinson's, and Huntington's disease. Tracking of stem cells with noninvasive imaging technologies provides insight into location, migration, and proliferation of the cells-key features for a possible clinical translation. This chapter describes a multimodal and noninvasive approach employing magnetic resonance imaging (MRI) and bioluminescence imaging (BLI), both of which offer the opportunity for repetitive measurements on the same individual, revealing the full temporal profile of cell dynamics. The combination of these modalities allows the simultaneous investigation of different aspects of the graft fate. We will present the detailed protocol for noninvasive multimodal tracking of labeled and transplanted neural stem cells, specifically optimized for brain applications, which allows repetitive assessment of localization as well as identification of cell viability and cell quantity after transplantation.

Tracking stem cells for cellular therapy in stroke

Stem cell transplantation has emerged as a promising treatment strategy for stroke. The development of effective ways to monitor transplanted stem cells is essential to understand how stem cell transplantation enhances stroke recovery and ultimately will be an indispensable tool for advancing stem cell therapy to the clinic. In this review, we describe existing methods of tracking transplanted stem cells in vivo, including optical imaging, magnetic resonance imaging (MRI), and positron emission tomography (PET), with emphasis on the benefits and drawbacks of each imaging approach. Key considerations such as the potential impact of each tracking system on stem cell function, as well as its relative applicability to humans are discussed. Finally, we describe multi-modal imaging strategies as a more comprehensive method to track transplanted stem cells in the stroke-injured brain.

Effects of acute hypoxia/acidosis on intracellular pH in differentiating neural progenitor cells

The response of differentiating mouse neural progenitor cells, migrating out from neurospheres, to conditions simulating ischemia (hypoxia and extracellular or intracellular acidosis) was studied. We show here, by using BCECF and single cell imaging to monitor intracellular pH (pH(i)), that two main populations can be distinguished by exposing migrating neural progenitor cells to low extracellular pH or by performing an acidifying ammonium prepulse. The cells dominating at the periphery of the neurosphere culture, which were positive for neuron specific markers MAP-2, calbindin and NeuN had lower initial resting pH(i) and could also easily be further acidified by lowering the extracellular pH. Moreover, in this population, a more profound acidification was seen when the cells were acidified using the ammonium prepulse technique. However, when the cell population was exposed to depolarizing potassium concentrations no alterations in pH(i) took place in this population. In contrast, depolarization caused an increase in pH(i) (by 0.5 pH units) in the cell population closer to the neurosphere body, which region was positive for the radial cell marker (GLAST). This cell population, having higher resting pH(i) (pH 6.9-7.1) also responded to acute hypoxia. During hypoxic treatment the resting pH(i) decreased by 0.1 pH units and recovered rapidly after reoxygenation. Our results show that migrating neural progenitor cells are highly sensitive to extracellular acidosis and that irreversible damage becomes evident at pH 6.2. Moreover, our results show that a response to acidosis clearly distinguishes two individual cell populations probably representing neuronal and radial cells.

Effects of adipose tissue stem cell concurrent with greater omentum on experimental long-bone healing in dog

Repair of large bone defects resulting from trauma, tumors, and osteitis is a current challenge to surgeons. Adipose-derived adult stem cells (ASCs) are multipotent cells that are able to differentiate into osteoblasts in the presence of certain factors. In this study, the role of greater omentum as a scaffold incorporation of ASCs was evaluated in long-bone defect healing in dog model. Sixteen 3-4-year-old, male adult mongrel dogs, weighing 25.2 ± 3.5 kg, were used in this study. In the control group (n = 4), the defect was left empty. In the omental group (n = 4), the defect was filled with harvested omentum. In the omental-ASCs group (n = 4), the defect was filled with omentum and 1 mL of ASCs was injected into the grafted omentum. In the omental-culture medium group (n = 4), 1 mL of culture medium was injected into the grafted omentum. Finally, the injured radial bones were fixed with plate and screw. Radiographs of each forelimb was taken postoperatively on the first day and at the second, fourth, sixth, and eighth weeks postinjury to evaluate bone formation, union, and remodeling of the defect. The operated radii were removed on the 56th postoperative day and were histopathologically evaluated. In this study, both omental-culture medium and omental-ASCs groups demonstrated superior osteogenic potential in healing the radial bone defect. Compared to those of the omental and control groups, more advanced bone healing criteria were present in the omental-culture medium and omental-ASCs groups at radiological and histopathological levels at 8 weeks postsurgery.

Comparison of red-shifted firefly luciferase Ppy RE9 and conventional Luc2 as bioluminescence imaging reporter genes for in vivo imaging of stem cells

One critical issue for noninvasive imaging of transplanted bioluminescent cells is the large amount of light absorption in tissue when emission wavelengths below 600 nm are used. Luciferase with a red-shifted spectrum can potentially bypass this limitation. We assessed and compared a mutant of firefly luciferase (Ppy RE9, PRE9) against the yellow luciferase luc2 gene for use in cell transplantation studies. C17.2 neural stem cells expressing PRE9-Venus and luc2-Venus were sorted by flow cytometry and assessed for bioluminescence in vitro in culture and in vivo after transplantation into the brain of immunodeficient Rag2-/- mice. We found that the luminescence from PRE9 was stable, with a peak emission at 620 nm, shifted to the red compared to that of luc2. The emission peak for PRE9 was pH-independent, in contrast to luc2, and much less affected by tissue absorbance compared to that of luc2. However, the total emitted light radiance from PRE9 was substantially lower than that of luc2, both in vitro and in vivo. We conclude that PRE9 has favorable properties as compared to luc2 in terms of pH independence, red-shifted spectrum, tissue light penetration, and signal quantification, justifying further optimization of protein expression and enzymatic activity.

In vivo imaging of cell transplants in experimental ischemia

The therapeutic potential of stem cells for regeneration after cerebral lesion has become of great interest. This is particularly so for neurodegenerative diseases as well as for stroke. Contrary to more conventional, cerebroprotective treatment approaches, the focus of regeneration lies in a longer time window during the chronic phase of the lesion evolution. Thus, in order to assess the true potential of a treatment strategy and to investigate the underlying mechanisms, observation of the temporal profile of both the cell dynamics as well as the organ response to the treatment is of paramount importance. This need for intraindividual longitudinal studies can be optimally met by the application of noninvasive imaging modalities. This chapter presents in breadth the potential of noninvasive imaging modalities for cell tracking with application focus to experimental stroke. While the lion's share of discussed studies is based on MRI, we have also included the contributions of positron emission tomography and of the increasingly important optical imaging modality.

Migration and fate of therapeutic stem cells in different brain disease models

Stem cells have a number of properties, which make them excellent candidates for the treatment of various neurologic disorders, the most important of which being their ability to migrate to and differentiate predictably at sites of pathology in the brain. The disease-directed migration and well-characterized differentiation patterns of stem cells may eventually provide a powerful tool for the treatment of both localized and diffuse disease processes within the human brain. A thorough understanding of the molecular mechanisms governing their migratory properties and their choice between different differentiation programs is essential if these cells are to be used therapeutically in humans. This review focuses on summarizing the migration and differentiation of therapeutic neural and mesenchymal stem cells in different disease models in the brain and also discusses the promise of these cells to eventually treat various forms of neurologic disease.

Establishment of a real-time, quantitative, and reproducible mouse model of Staphylococcus osteomyelitis using bioluminescence imaging

Osteomyelitis remains a serious problem in the orthopedic field. There are only a few animal models in which the quantity and distribution of bacteria can be reproducibly traced. Here, we established a real-time quantitative mouse model of osteomyelitis using bioluminescence imaging (BLI) without sacrificing the animals. A bioluminescent strain of Staphylococcus aureus was inoculated into the femurs of mice. The bacterial photon intensity (PI) was then sequentially measured by BLI. Serological and histological analyses of the mice were performed. The mean PI peaked at 3 days, and stable signals were maintained for over 3 months after inoculation. The serum levels of interleukin-6, interleukin-1β, and C-reactive protein were significantly higher in the infected mice than in the control mice on day 7. The serum monocyte chemotactic protein 1 level was also significantly higher in the infected group at 12 h than in the control group. A significantly higher proportion of granulocytes was detected in the peripheral blood of the infected group after day 7. Additionally, both acute and chronic histological manifestations were observed in the infected group. This model is useful for elucidating the pathophysiology of both acute and chronic osteomyelitis and to assess the effects of novel antibiotics or antibacterial implants.

MRI stem cell tracking for therapy in experimental cerebral ischemia

Magnetic resonance has an established role in investigations on the evolution of stroke and the assessment of therapeutic strategies in experimental animals. Here we show that the technique has also an important place for the study of stem cell-mediated regenerative therapies after stroke. We review the literature by bridging from the methodological aspects of stem cell labeling via grafting and monitoring of cell dynamics after implantation into the brain all the way to MRI's role in analyzing the stem cell-mediated functional improvement. Thus, we have aimed at a view combining the focus on the monitoring of the cell activities with the aspect of lesion evolution while including also the essence of a potential functional improvement by the implantation of stem cells following stroke.

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.

DNA nanoparticles: detection of long-term transgene activity in brain using bioluminescence imaging

In this study, we used bioluminescence imaging (BLI) to track long-term transgene activity following the transfection of brain cells using a nonviral gene therapy technique. Formulations of deoxyribonucleic acid (DNA) combined with 30-mer lysine polymers (substituted with 10 kDa polyethylene glycol) form nanoparticles that transfect brain cells in vivo and produce transgene activity. Here we show that a single intracerebral injection of these DNA nanoparticles (DNPs) into the rat cortex, striatum, or substantia nigra results in long-term and persistent luciferase transgene activity over an 8- to 11-week period as evaluated by in vivo BLI analysis, and single injections of DNPs into the mouse striatum showed stable luciferase transgene activity for 1 year. Compacted DNPs produced in vivo signals 7- to 34-fold higher than DNA alone. In contrast, ex vivo BLI analysis, which is subject to less signal quenching from surrounding tissues, demonstrated a DNP to DNA alone ratio of 76- to 280-fold. Moreover, the ex vivo BLI analysis confirmed that signals originated from the targeted brain structures. In summary, BLI permits serial analysis of luciferase transgene activity at multiple brain locations following gene transfer with DNPs. Ex vivo analysis may permit more accurate determination of relative activities of gene transfer vectors.

Amniotic liquid derived stem cells as reservoir of secreted angiogenic factors capable of stimulating neo-arteriogenesis in an ischemic model

Most urgent health problems are related to a blood vessel formation failure. The use of stem cells from different sources or species for both in vitro and in vivo engineering of endothelium does not necessarily imply their direct commitment towards a vascular phenotype. In the present study, we used human amniotic fluid stem cells (AFSC) to evoke a strong angiogenic response in murine recipients, in terms of host guided-regeneration of new vessels, and we demonstrated that the AFSC secretome is responsible for the vascularising properties of these cells. We indentified in AFSC conditioned media (ACM) pro-angiogenic soluble factors, such as MCP-1, IL-8, SDF-1, VEGF. Our in vitro results suggest that ACM are cytoprotective, pro-differentiative and chemoattractive for endothelial cells. We also tested ACM on a pre-clinical model of hind-limb ischemic mouse, concluding that ACM contain mediators that promote the neo-arteriogenesis, as remodelling of pre-existing collateral arteries to conductance vessels, thus preventing the capillary loss and the tissue necrosis of distal muscles. In line with the current regenerative medicine trend, in the present study we assert the concept that stem cell-secreted mediators can guide the tissue repair by stimulating or recruiting host reparative cells.

In vivo Tracking of Transplanted Bone Marrow-Derived Mesenchymal Stem Cells in a Murine Model of Stroke by Bioluminescence Imaging

OBJECTIVE

This study was designed to validate the cell trafficking efficiency of the in vivo bioluminescence image (BLI) study in the setting of transplantation of the luciferase expressing bone marrow-derived mesenchymal stem cells (BMSC), which were delivered at each different time after transient middle cerebral artery occlusion (MCAO) in a mouse model.

METHODS

Transplanting donor BMSC were prepared by primary cell culture from transgenic mouse expressing luciferase (LUC). Transient focal infarcts were induced in 4-6-week-old male nude mice. The experiment mice were divided into five groups by the time of MSC transplantation : 1) sham-operation group, 2) 2-h group, 3) 1-day group, 4) 3-day group, and 5) 1- week group. BLI for detection of spatial distribution of transplanted MSC was performed by detecting emitted photons. Migration of the transplanted cells to the infarcted area was confirmed by histological examinations. Differences between groups were evaluated by paired t-test.

RESULTS

A focal spot of bioluminescence was observed at the injection site on the next day after transplantation by signal intensity of bioluminescence. After 4 weeks, the mean signal intensities of 2-h, 1-day, 3-day, and 1-week group were 2.6×10(7) ± 7.4×10(6), 6.1×10(6) ± 1.2×10(6), 1.7×10(6) ± 4.4×10(5), and 8.9×10(6) ± 9.5×10(5), respectively. The 2-h group showed significantly higher signal intensity (p < 0.01). The engrafted BMSC showed around the infarct border zones on immunohistochemical examination. The counts of LUC-positive cells revealed the highest number in the 2-h group, in agreement with the results of BLI experiments (p < 0.01).

CONCLUSION

In this study, the results suggested that the transplanted BMSC migrated to the infarct border zone in BLI study and the higher signal intensity of LUC-positive cells seen in 2 hrs after MSC transplantation in MCAO mouse model. In addition, noninvasive imaging in real time is an ideal method for tracking stem cell transplantation. This method can be widely applied to various research fields of cell transplantation therapy.

Combined fluorescence and X-Ray tomography for quantitative in vivo detection of fluorophore

Initial results from a novel dual modality preclinical imager which combines non-contact fluorescence tomography (FT) and x-ray computed tomography (CT) for preclinical functional and anatomical in vivo imaging are presented. The anatomical data from CT provides a priori information to the FT reconstruction to create overlaid functional and anatomical images with accurate localization and quantification of fluorophore distribution. Phantoms with inclusions containing Indocyanine-Green (ICG), and with heterogeneous backgrounds including iodine in compartments at different concentrations for CT contrast, have been imaged with the dual modality FT/CT system. Anatomical information from attenuation maps and optical morphological information from absorption and scattering maps are used as a priori information in the FT reconstruction. Although ICG inclusions can be located without the a priori information, the recovered ICG concentration shows 75% error. When the a priori information is utilized, the ICG concentration can be recovered with only 15% error. Developing the ability to accurately quantify fluorophore concentration in anatomical regions of interest may provide a powerful tool for in vivo small animal imaging.