Disease Targets and Strategies for the Therapeutic Modulation of Endogenous Neural Stem and Progenitor Cells

miR-18a counteracts AKT and ERK activation to inhibit the proliferation of pancreatic progenitor cells

Activation of endogenous stem/progenitor cells to repair injured tissues is an ideal option for disease treatment. However, adult pancreatic progenitor cells remain in a quiescent state in vivo. Thus, it is difficult to stimulate proliferation and differentiation in these progenitor cells, and the cause remains elusive. miR-17-92 cluster miRNAs are highly conserved in mammals and are expressed in multiple tissue stem/progenitor cells, but their role in pancreatic progenitor cells are less well known. In the present study, we demonstrate that miR-18a, but not the other members of the miR-17-92 gene cluster, inhibits the proliferation of pancreatic progenitor cells in vitro and ex vivo. miR-18a inhibits proliferation of adult pancreatic progenitor cells through arresting the cell cycle at G1 stage, indicating that miR-18a plays a role in keeping the adult pancreatic progenitor cells in quiescence. miR-18a inhibits pancreatic progenitor proliferation by targeting the gene expressions of connective tissue growth factor (CTGF), neural precursor cell expressed, developmentally down-regulated 9 (Nedd9), and cyclin dependent kinase 19 (CDK19), as well as by suppressing activation of the proliferation-related signaling pathways phosphatidylinositol 3-kinase–protein kinase B (PI3K/AKT) and extracellular signal-regulated kinase (ERK).

In Vivo Expression of Reprogramming Factors Increases Hippocampal Neurogenesis and Synaptic Plasticity in Chronic Hypoxic-Ischemic Brain Injury

Neurogenesis and synaptic plasticity can be stimulated in vivo in the brain. In this study, we hypothesized that in vivo expression of reprogramming factors such as Klf4, Sox2, Oct4, and c-Myc would facilitate endogenous neurogenesis and functional recovery. CD-1® mice were induced at 1 week of age by unilaterally carotid artery ligation and exposure to hypoxia. At 6 weeks of age, mice were injected GFP only or both four reprogramming factors and GFP into lateral ventricle. Passive avoidance task and open field test were performed to evaluate neurobehavioral function. Neurogenesis and synaptic activity in the hippocampus were evaluated using immunohistochemistry, qRT-PCR, and/or western blot analyses. Whereas BrdU⁺GFAP⁺ cells in the subgranular zone of the hippocampus were not significantly different, the numbers of BrdU⁺βIII-tubulin⁺ and BrdU⁺NeuN⁺ cells were significantly higher in treatment group than control group. Expressions of synaptophysin and PSD-95 were also higher in treatment group than control group. Importantly, passive avoidance task and open field test showed improvement in long-term memory and decreased anxiety in treatment group. In conclusion, in vivo expression of reprogramming factors improved behavioral functions in chronic hypoxic-ischemic brain injury. The mechanisms underlying these repair processes included endogenous neurogenesis and synaptic plasticity in the hippocampus.

Induction of Neurorestoration From Endogenous Stem Cells

Neural stem cells (NSCs) persist in the subventricular zone lining the ventricles of the adult brain. The resident stem/progenitor cells can be stimulated in vivo by neurotrophic factors, hematopoietic growth factors, magnetic stimulation, and/or physical exercise. In both animals and humans, the differentiation and survival of neurons arising from the subventricular zone may also be regulated by the trophic factors. Since stem/progenitor cells present in the adult brain and the production of new neurons occurs at specific sites, there is a possibility for the treatment of incurable neurological diseases. It might be feasible to induce neurogenesis, which would be particularly efficacious in the treatment of striatal neurodegenerative conditions such as Huntington's disease, as well as cerebrovascular diseases such as ischemic stroke and cerebral palsy, conditions that are widely seen in the clinics. Understanding of the molecular control of endogenous NSC activation and progenitor cell mobilization will likely provide many new opportunities as therapeutic strategies. In this review, we focus on endogenous stem/progenitor cell activation that occurs in response to exogenous factors including neurotrophic factors, hematopoietic growth factors, magnetic stimulation, and an enriched environment. Taken together, these findings suggest the possibility that functional brain repair through induced neurorestoration from endogenous stem cells may soon be a clinical reality.

Translational research and therapeutic applications of stem cell transplantation in periodontal regenerative medicine

Stem cells have received a great deal of interest from the research community as potential therapeutic "tools" for a variety of chronic debilitating diseases that lack clinically effective therapies. Stem cells are also of interest for the regeneration of tooth-supporting tissues that have been lost to periodontal disease. Indeed, substantial data have demonstrated that the exogenous administration of stem cells or their derivatives in preclinical animal models of periodontal defects can restore damaged tissues to their original form and function. As we discuss here, however, considerable hurdles must be overcome before these findings can be responsibly translated to novel clinical therapies. Generally, the application of stem cells for periodontal therapy in clinics will not be realized until the best cell(s) to use, the optimal dose, and an effective mode of administration are identified. In particular, we need to better understand the mechanisms of action of stem cells after transplantation in the periodontium and to learn how to preciously control stem cell fates in the pathological environment around a tooth. From a translational perspective, we outline the challenges that may vary across preclinical models for the evaluation of stem cell therapy in situations that require periodontal reconstruction and the safety issues that are related to clinical applications of human stem cells. Although clinical trials that use autologous periodontal ligament stem cells have been approved and have already been initiated, proper consideration of the technical, safety, and regulatory concerns may facilitate, rather than inhibit, the clinical translation of new therapies.

White matter dementia

White matter dementia (WMD) is a syndrome introduced in 1988 to highlight the potential of cerebral white matter disorders to produce cognitive loss of sufficient severity to qualify as dementia. Neurologists have long understood that such a syndrome can occur, but the dominance of gray matter as the locus of higher function has strongly directed neurobehavioral inquiry to the cerebral cortex while white matter has received less attention. Contemporary neuroimaging has been crucial in enabling the recognition of white matter abnormalities in a host of disorders, and the correlation of these changes with cognitive performance. Comprising about half the brain, white matter is prominently or exclusively involved in well over 100 disorders, in each of which white matter dysfunction can potentially cause or contribute to dementia. Neuropsychological findings from ten categories of white matter disorder lead to a convergence of findings that document remarkable neurobehavioral commonality among the dementias produced. More recently, the syndrome of mild cognitive dysfunction (MCD) has been introduced to expand the concept of WMD by proposing a precursor syndrome related to early white matter neuropathology. WMD and MCD inform the understanding of how white matter contributes to normal and abnormal cognition, and the specific neuroanatomic focus of these syndromes may enhance the diagnosis and treatment of many disabling disorders that do not primarily implicate the cerebral cortex. Forming essential connections within widely distributed neural networks, white matter is critical for rapid and efficient information transfer that complements the information processing of gray matter. As neuroimaging continues to advance, further information on white matter structure can be expected, and behavioral neurology will play a central role in elucidating the functional significance of these emerging data. By emphasizing the contribution of myelinated systems to higher function, the study of white matter and cognition represents investigation of the basic neuroscience of human behavior.

Differential pathotropism of non-immortalized and immortalized human neural stem cell lines in a focal demyelination model

Cell therapy is reaching the stage of phase I clinical trials for post-traumatic, post-ischemic, or neurodegenerative disorders, and the selection of the appropriate cell source is essential. In order to assess the capacity of different human neural stem cell lines (hNSC) to contribute to neural tissue regeneration and to reduce the local inflammation after an acute injury, we transplanted GMP-grade non-immortalized hNSCs and v-myc (v-IhNSC), c-myc T58A (T-IhNSC) immortalized cells into the corpus callosum of adult rats after 5 days from focal demyelination induced by lysophosphatidylcholine. At 15 days from transplantation, hNSC and T-IhNSC migrated to the lesioned area where they promoted endogenous remyelination and differentiated into mature oligodendrocytes, while the all three cell lines were able to integrate in the SVZ. Moreover, where demyelination was accompanied by an inflammatory reaction, a significant reduction of microglial cells' activation was observed. This effect correlated with a differential migratory pattern of transplanted hNSC and IhNSC, significantly enhanced in the former, thus suggesting a specific NSC-mediated immunomodulatory effect on the local inflammation. We provide evidence that, in the subacute phase of a demyelination injury, different human immortalized and non-immortalized NSC lines, all sharing homing to the stem niche, display a differential pathotropism, both through cell-autonomous and non-cell autonomous effects. Overall, these findings promote IhNSC as an inexhaustible cell source for large-scale preclinical studies and non-immortalized GMP grade hNSC lines as an efficacious, safe, and reliable therapeutic tool for future clinical applications.

Process optimization and biocompatibility of cell carriers suitable for automated magnetic manipulation

There is increasing demand for automated cell reprogramming in the fields of cell biology, biotechnology and the biomedical sciences. Microfluidic-based platforms that provide unattended manipulation of adherent cells promise to be an appropriate basis for cell manipulation. In this study we developed a magnetically driven cell carrier to serve as a vehicle within an in vitro environment. To elucidate the impact of the carrier on cells, biocompatibility was estimated using the human adenocarcinoma cell line Caco-2. Besides evaluation of the quality of the magnetic carriers by field emission scanning electron microscopy, the rate of adherence, proliferation and differentiation of Caco-2 cells grown on the carriers was quantified. Moreover, the morphology of the cells was monitored by immunofluorescent staining. Early generations of the cell carrier suffered from release of cytotoxic nickel from the magnetic cushion. Biocompatibility was achieved by complete encapsulation of the nickel bulk within galvanic gold. The insulation process had to be developed stepwise and was controlled by parallel monitoring of the cell viability. The final carrier generation proved to be a proper support for cell manipulation, allowing proliferation of Caco-2 cells equal to that on glass or polystyrene as a reference for up to 10 days. Functional differentiation was enhanced by more than 30% compared with the reference. A flat, ferromagnetic and fully biocompatible carrier for cell manipulation was developed for application in microfluidic systems. Beyond that, this study offers advice for the development of magnetic cell carriers and the estimation of their biocompatibility.

Stem cells: a model for screening, discovery and development of drugs

The identification of normal and cancerous stem cells and the recent advances made in isolation and culture of stem cells have rapidly gained attention in the field of drug discovery and regenerative medicine. The prospect of performing screens aimed at proliferation, directed differentiation, and toxicity and efficacy studies using stem cells offers a reliable platform for the drug discovery process. Advances made in the generation of induced pluripotent stem cells from normal or diseased tissue serves as a platform to perform drug screens aimed at developing cell-based therapies against conditions like Parkinson’s disease and diabetes. This review discusses the application of stem cells and cancer stem cells in drug screening and their role in complementing, reducing, and replacing animal testing. In addition to this, target identification and major advances in the field of personalized medicine using induced pluripotent cells are also discussed.

Myoblast-derived neuronal cells form glutamatergic neurons in the mouse cerebellum

Production of neurons from non-neural cells has far-reaching clinical significance. We previously found that myoblasts can be converted to a physiologically active neuronal phenotype by transferring a single recombinant transcription factor, REST-VP16, which directly activates target genes of the transcriptional repressor, REST. However, the neuronal subtype of M-RV cells and whether they can establish synaptic communication in the brain have remained unknown. M-RV cells engineered to express green fluorescent protein (M-RV-GFP) had functional ion channels but did not establish synaptic communication in vitro. However, when transplanted into newborn mice cerebella, a site of extensive postnatal neurogenesis, these cells expressed endogenous cerebellar granule precursors and neuron proteins, such as transient axonal glycoprotein-1, neurofilament, type-III β-tubulin, superior cervical ganglia-clone 10, glutamate receptor-2, and glutamate decarboxylase. Importantly, they exhibited action potentials and were capable of receiving glutamatergic synaptic input, similar to the native cerebellar granule neurons. These results suggest that M-RV-GFP cells differentiate into glutamatergic neurons, an important neuronal subtype, in the postnatal cerebellar milieu. Our findings suggest that although activation of REST-target genes can reprogram myoblasts to assume a general neuronal phenotype, the subtype specificity may then be directed by the brain microenvironment.

Transient glutathione depletion determines terminal differentiation in HL-60 cells

To better define the role of glutathione (GSH) in cell differentiation, the present study measured GSH concentrations during terminal HL-60 cell differentiation, in the presence and absence of differentiation-inducing agents, and in the presence and absence of GSH altering agents. Interestingly, there was a small transient increase in intracellular GSH levels during dimethyl sulfoxide (DMSO) or 1α,25-dihydroxyvitamin D3 (VD3) induced differentiation. This increase coincided with an increase in nitroblue tetrazolium (NBT) reduction capacity, a measure of superoxide anion production, but there was no apparent change in the GSH/glutathione disulfide (GSSG) ratio. Surprisingly, treatment of cells with low doses of 1-chloro-2,4-dinitrobenzene (CDNB; 5 µM) or diethylmaleate (DEM; 0.5 mM), which transiently deplete GSH levels to about 40% of control levels, resulted in enhanced differentiation of HL-60 cells exposed to VD3 or all-trans-retinoic acid (ATRA), as well as under un-induced conditions (i.e., spontaneous differentiation). Enhanced differentiation occurred when cells were treated with the GSH-depleting agents 4 hours after treatment with differentiation inducers. These findings indicate that intracellular GSH levels are regulated in a complex fashion during HL-60 cell differentiation, and that transient GSH depletion using low doses of CDNB and DEM enhances the differentiation process.

Cell delivery: from cell transplantation to organ engineering

Cell populations derived from adult tissue and stem cells possess a great expectation for the treatment of several diseases. Great efforts have been made to generate cells with therapeutic impact from stem cells. However, it is clear that the development of systems to deliver such cells to induce efficient engraftment, growth, and function is a real necessity. Biologic and artificial scaffolds have received significant attention for their potential therapeutic application when use to form tissues in vitro and facilitate engraftment in vivo. Ultimately more sophisticated methods for decellularization of organs have been successfully used in tissue engineering and regenerative medicine applications. These decellularized tissues and organs appear to provide bioactive molecules and bioinductive properties to induce homing, differentiation, and proliferation of cells. The combination of decellularized organs and stem cells may dramatically improve the survival, engraftment, and fate control of transplanted stem cells and their ultimate clinical utility, opening the doors to a new era of organ engineering.

Robust generation of oligodendrocyte progenitors from human neural stem cells and engraftment in experimental demyelination models in mice

BACKGROUND

Cell-based therapy holds great promises for demyelinating diseases. Human-derived fetal and adult oligodendrocyte progenitors (OPC) gave encouraging results in experimental models of dysmyelination but their limited proliferation in vitro and their potential immunogenicity might restrict their use in clinical applications. Virtually unlimited numbers of oligodendroglial cells could be generated from long-term self-renewing human (h)-derived neural stem cells (hNSC). However, robust oligodendrocyte production from hNSC has not been reported so far, indicating the need for improved understanding of the molecular and environmental signals controlling hNSC progression through the oligodendroglial lineage. The aim of this work was to obtain enriched and renewable cultures of hNSC-derived oligodendroglial cells by means of epigenetic manipulation.

METHODOLOGY/PRINCIPAL FINDINGS

We report here the generation of large numbers of hNSC-derived oligodendroglial cells by concurrent/sequential in vitro exposure to combinations of growth factors (FGF2, PDGF-AA), neurotrophins (NT3) and hormones (T3). In particular, the combination FGF2+NT3+PDGF-AA resulted in the maintenance and enrichment of an oligodendroglial cell population displaying immature phenotype (i.e., proliferation capacity and expression of PDGFRalpha, Olig1 and Sox10), limited self-renewal and increased migratory activity in vitro. These cells generate large numbers of oligodendroglial progeny at the early stages of maturation, both in vitro and after transplantation in models of CNS demyelination.

CONCLUSIONS/SIGNIFICANCE

We describe a reliable method to generate large numbers of oligodendrocytes from a renewable source of somatic, non-immortalized NSC from the human foetal brain. We also provide insights on the mechanisms underlying the pro-oligodendrogenic effect of the treatments in vitro and discuss potential issues responsible for the limited myelinating capacity shown by hNSC-derived oligodendrocytes in vivo.

Tissue-derived stem and progenitor cells

The characterization and isolation of various stem cell populations, from embryonic through tissue-derived stem cells, have led a rapid growth in the field of stem cell research. These research efforts have often been interrelated as to the markers that identify a select cell population are frequently analyzed to determine their expression in cells of distinct organs/tissues. In this review, we will expand the current state of research involving select tissue-derived stem cell populations including the liver, central nervous system, and cardiac tissues as examples of the success and challenges in this field of research. Lastly, the challenges of clinical therapies will be discussed as it applies to these unique cell populations.

Vascular endothelial growth factor-stimulated cerebral microvascular endothelial cells mediate the recruitment of neural stem cells to the neurovascular niche

Endogenous and transplanted neural stem cells (NSC) are highly migratory and display a unique tropism for areas of neuro-pathology. However, signals controlling NSC motility in health and disease are still ill-defined. NSC appear to be intimately associated with the cerebral vasculature and angiogenesis is a hallmark of many neurological disorders. This has led us to investigate the influence of quiescent and angiogenically active human endothelial cells on human NSC migration. In vivo we observed frequent perivascular accumulation of human NSC in the proximity of cerebral microvessels upon induction of angiogenesis by cerebral infusion of vascular endothelial growth factor (VEGF) into the murine brain. We analyzed the in vitro effects of conditioned media from human endothelial cells before and after angiogenic stimulation with VEGF on the migration of human NSC in vitro. Non-stimulated endothelial cells induced a moderate chemotactic migration that was significantly enhanced after angiogenic activation by VEGF. In order to identify cytokines that may function as stimulators of NSC chemotaxis, we screened endothelial cell-conditioned media for the expression of 120 different cytokines. We identified PDGF-BB, RANTES, I-TAC, NAP-2, GROalpha, Ang-2, and M-CSF as endothelial cell-released chemoattractants for human NSC in vitro. VEGF-stimulated cerebral microvascular endothelial cells secreted higher levels of Ang-2 and GROalpha, which in part were responsible for the enhanced chemoattraction of NSC. Our findings support the hypothesis that the angiogenically active microvasculature modulates the local guidance of NSC through endothelial cell-derived chemoattractants.

Adult neural stem cells and their role in brain pathology

Stem cells are multipotent cells that can give rise to a differentiated progeny as well as self-renew. The balanced coordination of these two stem cell fates is essential for embryonic development and tissue homeostasis in the adult. Perturbed stem cell function contributes significantly to a variety of pathological conditions, eg impaired self-renewal capacity due to cellular senescence contributes to ageing, and degenerative diseases or impaired stem cell differentiation by oncogenic mutations contribute to cancer formation. This review focuses on the molecular mechanisms involved in regulating the normal function of neural stem cells in the adult mammalian brain and on the involvement of these cells in brain pathology.

Fate plasticity of adult hippocampal progenitors: biological relevance and therapeutic use

Adult hippocampal stem/progenitor cells (AHPs) continuously give rise to new neurons throughout life, which might be an important determinant of hippocampus-dependent function. Strikingly, the fate potential of AHPs is not restricted to the neuronal lineage because AHPs can be genetically induced to generate oligodendrocytes within their in vivo niche by AHP-specific ectopic expression of the basic-helix-loop-helix (bHLH) transcription factor achaete-scute complex-like 1 (ASCL1). Fate plasticity of AHPs is controlled by cell-autonomous and also niche-dependent mechanisms. Here, we discuss the biological importance and potential therapeutic applications of retained fate plasticity of AHPs in the adult mammalian brain in addition to the future scientific inquiries indicated by this finding.

Cell delivery mechanisms for tissue repair

Many cell populations, derived from both adult tissues and embryonic stem cells, show promise for the treatment of a variety of diseases. Although the major effort in stem cell therapies in the past has been identifying potentially therapeutic cells, it is now clear that developing systems to deliver these cells and promote their efficient engraftment will provide an equally challenging task. More sophisticated pretransplantation manipulations and material carriers may dramatically improve the survival, engraftment, and fate control of transplanted stem cells and their ultimate clinical utility.

The blood-brain barrier in health and chronic neurodegenerative disorders

The blood-brain barrier (BBB) is a highly specialized brain endothelial structure of the fully differentiated neurovascular system. In concert with pericytes, astrocytes, and microglia, the BBB separates components of the circulating blood from neurons. Moreover, the BBB maintains the chemical composition of the neuronal "milieu," which is required for proper functioning of neuronal circuits, synaptic transmission, synaptic remodeling, angiogenesis, and neurogenesis in the adult brain. BBB breakdown, due to disruption of the tight junctions, altered transport of molecules between blood and brain and brain and blood, aberrant angiogenesis, vessel regression, brain hypoperfusion, and inflammatory responses, may initiate and/or contribute to a "vicious circle" of the disease process, resulting in progressive synaptic and neuronal dysfunction and loss in disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and others. These findings support developments of new therapeutic approaches for chronic neurodegenerative disorders directed at the BBB and other nonneuronal cells of the neurovascular unit.