Neural stem cells in aging and disease

Potential effects of commonly applied drugs on neural stem cell proliferation and viability: A hypothesis-generating systematic review and meta-analysis

Neural stem cell (NSC) transplantation is an emerging and promising approach to combat neurodegenerative diseases. While NSCs can differentiate into neural cell types, many therapeutic effects are mediated by paracrine, "drug-like" mechanisms. Neurodegenerative diseases are predominantly a burden of the elderly who commonly suffer from comorbidities and thus are subject to pharmacotherapies. There is substantial knowledge about drug-drug interactions but almost nothing is known about a potential impact of pharmacotherapy on NSCs. Such knowledge is decisive for designing tailored treatment programs for individual patients. Previous studies revealed preliminary evidence that the anti-depressants fluoxetine and imipramine may affect NSC viability and proliferation. Here, we derive a hypothesis on how commonly applied drugs, statins and antihypertensives, may affect NSC viability, proliferation, and differentiation. We conducted a systematic review and meta-analysis looking at potential effects of commonly prescribed antihypertensive and antihyperlipidemic medication on NSC function. PubMed and Web of Science databases were searched on according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Publications were assessed against a priori established selection criteria for relevancy. A meta-analysis was then performed on data extracted from publications eligible for full text review to estimate drug effects on NSC functions. Our systematic review identified 1,017 potential studies, 55 of which were eligible for full text review. Out of those, 21 were included in the qualitative synthesis. The meta-analysis was performed on 13 publications; the remainder were excluded as they met exclusion criteria or lacked sufficient data to perform a meta-analysis. The meta-analysis revealed that alpha-2 adrenoceptor agonists, an anti-hypertensive drug class [p < 0.05, 95% confidence intervals (CI) = -1.54; -0.35], and various statins [p < 0.05, 95% CI = -3.17; -0.0694] had an inhibiting effect on NSC proliferation. Moreover, we present preliminary evidence that L-type calcium channel blockers and statins, particularly lovastatin, may reduce NSC viability. Although the data available in the literature is limited, there are clear indications for an impact of commonly applied drugs, in particular statins, on NSC function. Considering the modes of action of the respective drugs, we reveal plausible mechanisms by which this impact may be mediated, creating a testable hypothesis, and providing insights into how future confirmative research on this topic may be conducted.

Stem Cell-based Therapeutic and Diagnostic Approaches in Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative impairment mainly recognized by memory loss and cognitive deficits. However, the current therapies against AD are mostly limited to palliative medications, prompting researchers to investigate more efficient therapeutic approaches for AD, such as stem cell therapy. Recent evidence has proposed that extensive neuronal and synaptic loss and altered adult neurogenesis, which is perceived pivotal in terms of plasticity and network maintenance, occurs early in the course of AD, which exacerbates neuronal vulnerability to AD. Thus, regeneration and replenishing the depleted neuronal networks by strengthening the endogenous repair mechanisms or exogenous stem cells and their cargoes is a rational therapeutic approach. Currently, several stem cell-based therapies as well as stem cell products like exosomes, have shown promising results in the early diagnosis of AD.

OBJECTIVE

This review begins with a comparison between AD and normal aging pathophysiology and a discussion on open questions in the field. Next, summarizing the current stem cell-based therapeutic and diagnostic approaches, we declare the advantages and disadvantages of each method. Also, we comprehensively evaluate the human clinical trials of stem cell therapies for AD.

METHODOLOGY

Peer-reviewed reports were extracted through Embase, PubMed, and Google Scholar until 2021.

RESULTS

With several ongoing clinical trials, stem cells and their derivatives (e.g., exosomes) are an emerging and encouraging field in diagnosing and treating neurodegenerative diseases. Although stem cell therapies have been successful in animal models, numerous clinical trials in AD patients have yielded unpromising results, which we will further discuss.

Metabolic disorder in Alzheimer's disease

Alzheimer's disease (AD), a well known aging-induced neurodegenerative disease is related to amyloid proteinopathy. This proteinopathy occurs due to abnormalities in protein folding, structure and thereby its function in cells. The root cause of such kind of proteinopathy and its related neurodegeneration is a disorder in metabolism, rather metabolomics of the major as well as minor nutrients. Metabolomics is the most relevant "omics" platform that offers a great potential for the diagnosis and prognosis of neurodegenerative diseases as an individual's metabolome. In recent years, the research on such kinds of neurodegenerative diseases, especially aging-related disorders is broadened its scope towards metabolic function. Different neurotransmitter metabolisms are also involved with AD and its associated neurodegeneration. The genetic and epigenetic backgrounds are also noteworthy. In this review, the physiological changes of AD in relation to its corresponding biochemical, genetic and epigenetic involvements including its (AD) therapeutic aspects are discussed.

Aging and Alzheimer's disease: Comparison and associations from molecular to system level

Alzheimer's disease is the most prevalent cause of dementia, which is defined by the combined presence of amyloid and tau, but researchers are gradually moving away from the simple assumption of linear causality proposed by the original amyloid hypothesis. Aging is the main risk factor for Alzheimer's disease that cannot be explained by amyloid hypothesis. To evaluate how aging and Alzheimer's disease are intrinsically interwoven with each other, we review and summarize evidence from molecular, cellular, and system level. In particular, we focus on study designs, treatments, or interventions in Alzheimer's disease that could also be insightful in aging and vice versa.

Cholinergic and dopaminergic neuronal differentiation of human adipose tissue derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent cells that can differentiate into various cell types such as cartilage, bone, and fat cells. Recent studies have shown that induction of MSCs in vitro by growth factors including epidermal growth factor (EGF) and fibroblast growth factor (FGF2) causes them to differentiate into neural like cells. These cultures also express ChAT, a cholinergic marker; and TH, a dopaminergic marker for neural cells. To establish a protocol with maximum differentiation potential, we examined MSCs under three experimental culture conditions using neural induction media containing FGF2, EGF, BMP-9, retinoic acid, and heparin. Adipose-derived MSCs were extracted and expanded in vitro for 3 passages after reaching >80% confluency, for a total duration of 9 days. Cells were then characterized by flow cytometry for CD markers as CD44 positive and CD45 negative. MSCs were then treated with neural induction media and were characterized by morphological changes and Q-PCR. Differentiated MSCs expressed markers for immature and mature neurons; β Tubulin III (TUBB3) and MAP2, respectively, showing the neural potential of these cells to differentiate into functional neurons. Improved protocols for MSCs induction will facilitate and ensure the reproducibility and standard production of MSCs for therapeutic applications in neurodegenerative diseases.

Neural Progenitor Cells Promote Axonal Growth and Alter Axonal mRNA Localization in Adult Neurons

The inhibitory environment of the spinal cord and the intrinsic properties of neurons prevent regeneration of axons following CNS injury. However, both ascending and descending axons of the injured spinal cord have been shown to regenerate into grafts of embryonic neural progenitor cells (NPCs). Previous studies have shown that grafts composed of glial-restricted progenitors (GRPs) and neural-restricted progenitors (NRPs) can provide a permissive microenvironment for axon growth. We have used cocultures of adult rat dorsal root ganglion (DRG) neurons together with NPCs, which have shown significant enhancement of axon growth by embryonic rat GRP and GRPs/NRPs, both in coculture conditions and when DRGs are exposed to conditioned medium from the NPC cultures. This growth-promoting effect of NPC-conditioned medium was also seen in injury-conditioned neurons. DRGs cocultured with GRPs/NRPs showed altered expression of regeneration-associated genes at transcriptional and post-transcriptional levels. We found that levels of GAP-43 mRNA increased in DRG cell bodies and axons. However, hepcidin antimicrobial peptide (HAMP) mRNA decreased in the cell bodies of DRGs cocultured with GRPs/NRPs, which is distinct from the increase in cell body HAMP mRNA levels seen in DRGs after injury conditioning. Endogenous GAP-43 and β-actin mRNAs as well as reporter RNAs carrying axonally localizing 3'UTRs of these transcripts showed significantly increased levels in distal axons in the DRGs cocultured with GRPs/NRPs. These results indicate that axon growth promoted by NPCs is associated not only with enhanced transcription of growth-associated genes but also can increase localization of some mRNAs into growing axons.

Salvia miltiorrhiza: A source for anti-Alzheimer's disease drugs

CONTEXT

Alzheimer's disease (AD) is a devastating neurodegenerative disorder that affects millions of elderly people worldwide. However, no efficient therapeutic method for AD has yet been developed. Recently, Salvia miltiorrhiza Bunge (Lamiaceae), a well-known traditional Chinese medicine which is widely used for treating cardio-cerebrovascular, exerts multiple neuroprotective effects and is attracting increased attention for the treatment of AD.

OBJECTIVE

The objective of this study is to discuss the neuroprotective effects and neurogenesis-inducing activities of S. miltiorrhiza components.

METHODS

A detailed search using major electronic search engines (such as Pubmed, ScienceDirect, and Google Scholar) was undertaken with the search terms: Salvia miltiorrhiza, the components of S. miltiorrhiza such as salvianolic acid B, salvianolic acid A, danshensu, tanshinone I, tanshinone IIA, cryptotanshinone, dihydrotanshinone, and neuroprotection.

RESULTS

Salvia miltiorrhiza components exert multiple neuroprotective potentials relevant to AD, such as anti-amyloid-β, antioxidant, anti-apoptosis, acetylcholinesterase inhibition, and anti-inflammation. Moreover, S. miltiorrhiza promotes neurogenesis of neural progenitor cells/stem cells in vitro and in vivo.

CONCLUSIONS

The properties of S. miltiorrhiza indicate their therapeutic potential in AD via multiple mechanisms. In addition, S. miltiorrhiza provides lead compounds for developing new drugs against AD.

BMP2-SMAD signaling represses the proliferation of embryonic neural stem cells through YAP

Previous studies have shown that the Hippo pathway effector yes-associated protein (YAP) plays an important role in maintaining stem cell proliferation. However, the precise molecular mechanism of YAP in regulating murine embryonic neural stem cells (NSCs) remains largely unknown. Here, we show that bone morphogenetic protein-2 (BMP2) treatment inhibited the proliferation of mouse embryonic NSCs, that YAP was critical for mouse NSC proliferation, and that BMP2 treatment-induced inhibition of mouse NSC proliferation was abrogated by YAP knockdown, indicating that the YAP protein mediates the inhibitory effect of BMP2 signaling. Additionally, we found that BMP2 treatment reduced YAP nuclear translocation, YAP-TEAD interaction, and YAP-mediated transactivation. BMP2 treatment inhibited YAP/TEAD-mediated Cyclin D1 (ccnd1) expression, and knockdown of ccnd1 abrogated the BMP2-mediated inhibition of mouse NSC proliferation. Mechanistically, we found that Smad1/4, effectors of BMP2 signaling, competed with YAP for the interaction with TAED1 and inhibited YAP's cotranscriptional activity. Our data reveal mechanistic cross talk between BMP2 signaling and the Hippo-YAP pathway in murine NSC proliferation, which may be exploited as a therapeutic target in neurodegenerative diseases and aging.

The autophagy regulators Ambra1 and Beclin 1 are required for adult neurogenesis in the brain subventricular zone

Autophagy is a conserved proteolytic mechanism required for maintaining cellular homeostasis. The role of this process in vertebrate neural development is related to metabolic needs and stress responses, even though the importance of its progression has been observed in a number of circumstances, both in embryonic and in postnatal differentiating tissues. Here we show that the proautophagic proteins Ambra1 and Beclin 1, involved in the initial steps of autophagosome formation, are highly expressed in the adult subventricular zone (SVZ), whereas their downregulation in adult neural stem cells in vitro leads to a decrease in cell proliferation, an increase in basal apoptosis and an augmented sensitivity to DNA-damage-induced death. Further, Beclin 1 heterozygosis in vivo results in a significant reduction of proliferating cells and immature neurons in the SVZ, accompanied by a marked increase in apoptotic cell death. In sum, we propose that Ambra1- and Beclin 1-mediated autophagy plays a crucial role in adult neurogenesis, by controlling the survival of neural precursor cells.

Differentiation of neural stem/progenitor cells using low-intensity ultrasound

Herein, we report the evaluation of apoptosis, cell differentiation, neurite outgrowth and differentiation of neural stem/progenitor cells (NSPCs) in response to low-intensity ultrasound (LIUS) exposure. NSPCs were cultured under different conditions, with and without LIUS exposure, to evaluate the single and complex effects of LIUS. A lactic dehydrogenase assay revealed that the cell viability of NSPCs was maintained with LIUS exposure at an intensity range from 100 to 500 mW/cm(2). Additionally, in comparison with no LIUS exposure, the cell survival rate was improved with the combination of medium supplemented with nerve growth factor and LIUS exposure. Our results indicate that LIUS exposure promoted NSPC attachment and differentiation on a glass substrate. Neurite outgrowth assays revealed the generation of longer, thicker neurites after LIUS exposure. Furthermore, LIUS stimulation substantially increased the percentage of differentiating neural cells in NSPCs treated with nerve growth factor in comparison with the unstimulated group. The high percentage of differentiated neural cells indicated that LIUS induced neuronal networks denser than those observed in the unstimulated groups. Furthermore, the release of nitric oxide, an important small-molecule neurotransmitter, was significantly upregulated after LIUS exposure. It is therefore reasonable to suggest that LIUS promotes the differentiation of NSPCs into neural cells, induces neurite outgrowth and regulates nitric oxide production; thus, LIUS may be a potential candidate for NSPC induction and neural cell therapy.

Glutaminase 1 is essential for the differentiation, proliferation, and survival of human neural progenitor cells

Glutaminase is the enzyme that converts glutamine into glutamate, which serves as a key excitatory neurotransmitter and one of the energy providers for cellular metabolism. Previous studies have revealed that mice lacking glutaminase 1 (GLS1), the dominant isoform in the brain and kidney, died shortly after birth due to disrupted glutamatergic transmission, suggesting the critical role of GLS1 in the physiological functions of synaptic network. However, whether GLS1 regulates neurogenesis, a process by which neurons are generated from neural progenitor cells (NPCs), is unknown. Using a human NPC model, we found that both GLS1 isotypes, kidney-type glutaminase and glutaminase C, were upregulated during neuronal differentiation, which were correlated with the expression of neuronal marker microtubule-associated protein 2 (MAP-2). To study the functional impact of GLS1 on neurogenesis, we used small interference RNA targeting GLS1 and determined the expressions of neuronal genes by western blot, real-time polymerase chain reaction, and immunocytochemistry. siRNA silencing of GLS1 significantly reduced the expression of MAP-2, indicating that GLS1 is essential for neurogenesis. To unravel the specific process(es) of neurogenesis being affected, we further studied the proliferation and survival of NPCs in vitro. siRNA silencing of GLS1 significantly reduced the Ki67(+) and increased the TUNEL(+) cells, suggesting critical roles of GLS1 for the proliferation and survival of NPCs. Together, these data suggest that GLS1 is critical for proper functions of NPCs, including neuronal differentiation, proliferation, and survival.

Evaluation of proliferation of neural stem cells in vitro and in vivo

This unit describes two basic protocols for the detection of the proliferation of neural stem cells (NSC). The first one addresses cell proliferation in cultures, starting with primary cell cultures isolated from the mouse subventricular zone (SVZ), in which SVZ-derived NSC are kept in culture as neurospheres. By using this culture system, we are able to study different stages of adult neurogenesis, such as proliferation, differentiation, migration, and survival. Thus, in the first basic protocol, we describe two different techniques to evaluate cell proliferation based on EdU incorporation: (a) immunocytochemistry and (b) flow cytometry. EdU, a new thymidine analog, which is detected by a reproducible and sensitive method based on click chemistry, does not require DNA denaturation, as is the case with BrdU. Thus, co-labeling of EdU with other specific antibodies of extracellular or intracellular targets, as well as other DNA dyes, is possible. In the second basic protocol, we describe an in vivo assay to evaluate proliferation of NSC in the dentate gyrus of hippocampus of adult mice, by both BrdU and EdU detection. With this approach, it is also possible to study different stages of adult neurogenesis, by co-labeling thymidine analogs with other specific markers, such as doublecortin (DCX) or neuronal nuclei protein (NeuN).

Immunopharmacological intervention for successful neural stem cell therapy: New perspectives in CNS neurogenesis and repair

The pharmacological support and stimulation of endogenous and transplanted neural stem cells (NSCs) is a major challenge in brain repair. Trauma to the central nervous system (CNS) results in a distinct inflammatory response caused by local and infiltrating immune cells. This makes NSC-supported regeneration difficult due to the presence of inhibitory immune factors which are upregulated around the lesion site. The continual and dual role of the neuroinflammatory response leaves it difficult to decipher upon a single modulatory strategy. Therefore, understanding the influence of cytokines upon regulation of NSC self-renewal, proliferation and differentiation is crucial when designing therapies for CNS repair. There is a plethora of partially conflicting data in vitro and in vivo on the role of cytokines in modulating the stem cell niche and the milieu around NSC transplants. This is mainly due to the pleiotropic role of many factors. In order for cell-based therapy to thrive, treatment must be phase-specific to the injury and also be personalized for each patient, i.e. taking age, sex, neuroimmune and endocrine status as well as other key parameters into consideration. In this review, we will summarize the most relevant information concerning interleukin (IL)-1, IL-4, IL-10, IL-15, IFN-γ, the neuropoietic cytokine family and TNF-α in order to extract promising therapeutic approaches for further research. We will focus on the consequences of neuroinflammation on endogenous brain stem cells and the transplantation environment, the effects of the above cytokines on NSCs, as well as immunopharmacological manipulation of the microenvironment for potential therapeutic use.

Carbon nanotubes impregnated with subventricular zone neural progenitor cells promotes recovery from stroke

The present in vivo study was conducted to evaluate whether hydrophilic (HL) or hydrophobic (HP) carbon nanotubes (CNTs) impregnated with subventricular zone neural progenitor cells (SVZ NPCs) could repair damaged neural tissue following stroke. For this purpose, stroke damaged rats were transplanted with HL CNT-SVZ NPCs, HP CNT-SVZ NPCs, or SVZ NPCs alone for 1, 3, 5, and 8 weeks. Results showed that the HP CNT-SVZ NPC transplants improved rat behavior and reduced infarct cyst volume and infarct cyst area compared with the experimental control and the HL CNT-SVZ NPC and SVZ NPCs alone groups. The transplantation groups showed an increase in the expression of nestin (cell stemness marker) and proliferation which was evident with the increased number of doublecortin and bromodeoxyuridine double-stained immunopositive cells around the lesion site. But, these effects were more prominent in the HP CNT-SVZ NPC group compared with the other transplantation groups. The HP CNT-SVZ NPC and HL CNT-SVZ NPC transplants increased the number of microtubule-associated protein 2 (marker for neurons) and decreased the number of glial fibrillary acidic protein (marker for astroglial cells) positive cells within the injury epicenter. The majority of the transplanted HP CNT-SVZ NPCs collectively broadened around the ischemic injured region and the SVZ NPCs differentiated into mature neurons, attained the synapse morphology (TUJ1, synaptophysin), and decreased microglial activation (CD11b/c [OX-42]). For these reasons, this study provided the first evidence that CNTs can improve stem cell differentiation to heal stroke damage and, thus, deserve further attention.

Age-related proteomic changes in the subventricular zone and their association with neural stem/progenitor cell proliferation

In the mammalian central nervous system, generation of new neurons persists in the subventricular zone (SVZ) throughout life. However, the capacity for neurogenesis in this region declines with aging. Recent studies have examined the degree of these age-related neurogenic declines and the changes of cytoarchitecture of the SVZ with aging. However, little is known about the molecular changes in the SVZ with aging. In this study, we dissected the SVZs from rats aged postnatal day 28, 3 months, and 24 months. The SVZ tissues were processed for 2-D gel electrophoresis to identify protein changes following aging. Protein spots were subsequently subjected to mass spectrometry analysis to compare age-related alterations in the SVZ proteome. We also examined the level of cell proliferation in the SVZ in animals of these three age groups by using bromodeoxyuridine labeling. We found significant age-related changes in the expression of several proteins that play critical roles in the proliferation and survival of neural stem/progenitor cells in the SVZ. Among these proteins, glial fibrillary acidic protein, ubiquitin carboxy terminal hydrolase 1, glutathione S-transferase omega, and preproalbumin were increased with aging, whereas collapsin response-mediated protein 4 (CRMP-4), CRMP-5, and microsomal protease ER60 exhibited declines with aging. We have also observed a significant decline of neural stem/progenitor cell proliferation in the SVZ with aging. These alterations in protein expression in the SVZ with aging likely underlie the diminishing proliferative capacity of stem/progenitor cells in the aging brain.

Cyclooxygenase-1 is involved in the inhibition of hippocampal neurogenesis after lipopolysaccharide-induced neuroinflammation

Growing evidence indicates that neuroinflammation can alter adult neurogenesis by mechanisms as yet unclear. We have previously demonstrated that the neuroinflammatory response and neuronal damage after lipopolysaccharide (LPS) injection is reduced in cyclooxygenase-1 deficient (COX-1(-/-)) mice. In this study, we investigated the role of COX-1 on hippocampal neurogenesis during LPS-induced neuroinflammation, using COX-1(-/-) and wild type (WT) mice. We found that LPS-induced neuroinflammation resulted in the decrease of proliferation, survival and differentiation of hippocampal progenitor cells in WT but not in COX-1(-/-) mice. Thus, we demonstrate for the first time that COX-1 is involved in the inhibition of BrdU progenitor cells in proliferation and hippocampal neurogenesis after LPS. These results suggest that COX-1 may represent a viable therapeutic target to reduce neuroinflammation and promote neurogenesis in neurodegenerative diseases with a strong inflammatory component.

Developmental profiling of postnatal dentate gyrus progenitors provides evidence for dynamic cell-autonomous regulation

The dentate gyrus of the hippocampus is one of the most prominent regions in the postnatal mammalian brain where neurogenesis continues throughout life. There is tremendous speculation regarding the potential implications of adult hippocampal neurogenesis, though it remains unclear to what extent this ability becomes attenuated during normal aging, and what genetic changes in the progenitor population ensue over time. Using defined elements of the nestin promoter, we developed a transgenic mouse that reliably labels neural stem and early progenitors with green fluorescent protein (GFP). Using a combination of immunohistochemical and flow cytometry techniques, we characterized the progenitor cells within the dentate gyrus and created a developmental profile from postnatal day 7 (P7) until 6 months of age. In addition, we demonstrate that the proliferative potential of these progenitors is controlled at least in part by cell-autonomous cues. Finally, to identify what may underlie these differences, we performed stem cell-specific microarrays on GFP-expressing sorted cells from isolated P7 and postnatal day 28 (P28) dentate gyrus. We identified several differentially expressed genes that may underlie the functional differences that we observe in neurosphere assays from sorted cells and differentiation assays at these different ages. These data suggest that neural progenitors from the dentate gyrus are differentially regulated by cell-autonomous factors that change over time.

Effects of neuroinflammation on the regenerative capacity of brain stem cells

In the adult brain, neurogenesis under physiological conditions occurs in the subventricular zone and in the dentate gyrus. Although the exact molecular mechanisms that regulate neural stem cell proliferation and differentiation are largely unknown, several factors have been shown to affect neurogenesis. Decreased neurogenesis in the hippocampus has been recognized as one of the mechanisms of age-related brain dysfunction. Furthermore, in pathological conditions of the central nervous system associated with neuroinflammation, inflammatory mediators such as cytokines and chemokines can affect the capacity of brain stem cells and alter neurogenesis. In this review, we summarize the state of the art on the effects of neuroinflammation on adult neurogenesis and discuss the use of the lipopolysaccharide-model to study the effects of inflammation and reactive-microglia on brain stem cells and neurogenesis. Furthermore, we discuss the possible causes underlying reduced neurogenesis with normal aging and potential anti-inflammatory, pro-neurogenic interventions aimed at improving memory deficits in normal and pathological aging and in neurodegenerative diseases.

Stem cells for the treatment of neurodegenerative diseases

Stem cells offer an enormous pool of resources for the understanding of the human body. One proposed use of stem cells has been as an autologous therapy. The use of stem cells for neurodegenerative diseases has become of interest. Clinical applications of stem cells for Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, and multiple sclerosis will increase in the coming years, and although great care will need to be taken when moving forward with prospective treatments, the application of stem cells is highly promising.

Animal models of neurodegenerative diseases

Animal models of neurodegenerative disease are excellent tools for studying pathogenesis and therapies including cellular transplantation. In this chapter, we describe different models of Huntington's disease and Parkinson's disease, stereotactic surgery (used in creation of lesion models and transplantation) and finally transplantation studies in these models.

Behavior of hippocampal stem/progenitor cells following grafting into the injured aged hippocampus

Multipotent neural stem/progenitor cells (NSCs) from the embryonic hippocampus are potentially useful as donor cells to repopulate the degenerated regions of the aged hippocampus after stroke, epilepsy, or Alzheimer's disease. However, the efficacy of the NSC grafting strategy for repairing the injured aged hippocampus is unknown. To address this issue, we expanded FGF-2-responsive NSCs from the hippocampus of embryonic day 14 green fluorescent protein-expressing transgenic mice as neurospheres in vitro and grafted them into the hippocampus of 24-month-old F344 rats 4 days after CA3 region injury. Engraftment, migration, and neuronal/glial differentiation of cells derived from NSCs were analyzed 1 month after grafting. Differentiation of neurospheres in culture dishes or after placement on organotypic hippocampal slice cultures demonstrated that these cells had the ability to generate considerable numbers of neurons, astrocytes, and oligodendrocytes. Following grafting into the injured aged hippocampus, cells derived from neurospheres survived and dispersed, but exhibited no directed migration into degenerated or intact hippocampal cell layers. Phenotypic analyses of graft-derived cells revealed neuronal differentiation in 3%-5% of cells, astrocytic differentiation in 28% of cells, and oligodendrocytic differentiation in 6%-10% cells. The results demonstrate for the first time that NSCs derived from the fetal hippocampus survive and give rise to all three CNS phenotypes following transplantation into the injured aged hippocampus. However, grafted NSCs do not exhibit directed migration into lesioned areas or widespread neuronal differentiation, suggesting that direct grafting of primitive NSCs is not adequate for repair of the injured aged brain without priming the microenvironment.

Neurogenesis in diseases of the central nervous system

Neurogenesis is altered in ageing, and diseases of the central nervous system (CNS) such as neurodegenerative disorders. We discuss the process of neurogenesis, its relevance for disorders of the CNS, the dynamic nature of neurogenesis, how and why it may be abnormal in ageing, and disease, and possibilities to ameliorate abnormal neurogenesis in disease.

Novel cell therapy approaches for brain repair

Numerous reports elucidate that tissue-specific stem cells are phenotypically plastic and their differentiation pathways are not strictly delineated. Although the identity of all the epigenetic factors which may trigger stem cells to make a lineage selection are still unknown, the plasticity of adult stem cells opens new approaches for their application in the treatment of various disorders. There is increasing researcher interest in hematopoietic stem cells for treatment of not only blood-related diseases but also various unrelated disorders including neurodegenerative diseases. Human umbilical cord blood (hUCB) cells, due to their primitive nature and ability to develop into nonhematopoietic cells of various tissue lineages, including neural cells, may be useful as an alternative cell source for cell-based therapies requiring either the replacement of individual cell types and/or substitution of missing substances. Here we focus on recent findings showing the robustness of adult stem cells derived from hUCB and their potential as a source of transplant cells for the treatment of diseased or injured brains and spinal cords. Depending upon the pathological microenvironment in which the hUCB cells are introduced, neuroprotective and/or trophic effects of these cells, from release of various growth or anti-inflammatory factors to moderation of immune-inflammatory effectors, may be more likely than neural replacement. These protective effects may prove essential to maintaining restored tissue integrity over the course of various diseases or injuries.

Noggin signaling fromXenopus animal blastomere lineages promotes a neural fate in neighboring vegetal blastomere lineages

In Xenopus, localized factors begin to regionalize embryonic fates prior to the inductive interactions that occur during gastrulation. We previously reported that an animal-to-vegetal signal that occurs prior to gastrulation promotes primary spinal neuron fate in vegetal equatorial (C-tier) blastomere lineages. Herein we demonstrate that maternal mRNA encoding noggin is enriched in animal tiers and at low concentrations in the C-tier, suggesting that the neural fates of C-tier blastomeres may be responsive to early signaling from their neighboring cells. In support of this hypothesis, experimental alteration of the levels of Noggin from animal equatorial (B-tier) or BMP4 from vegetal (D-tier) blastomeres significantly affects the numbers of primary spinal neurons derived from their neighboring C-tier blastomeres. These effects are duplicated in blastomere explants isolated at cleavage stages and cultured in the absence of gastrulation interactions. Co-culture with animal blastomeres enhanced the expression of zygotic neural markers in C-tier blastomere explants, whereas co-culture with vegetal blastomeres repressed them. The expression of these markers in C-tier explants was promoted when Noggin was transiently added to the culture during cleavage/morula stages, and repressed with the transient addition of BMP4. Reduction of Noggin translation in B-tier blastomeres by antisense morpholino oligonucleotides significantly reduced the efficacy of neural marker induction in C-tier explants. These experiments indicate that early anti-BMP signaling from the animal hemisphere recruits vegetal equatorial cells into the neural precursor pool prior to interactions that occur during gastrulation.

Immortalized neural stem cells differ from nonimmortalized cortical neurospheres and cerebellar granule cell progenitors

Pluripotent neural stem cells (NSCs) have been used as replacement cells in a variety of neurological disease models. Among the many different NSCs that have been used to date, most robust results have been obtained with the immortalized neural stem cell line (C17.2) isolated from postnatal cerebellum. However, it is unclear if other NSCs isolated from different brain regions are similar in their potency as replacement therapies. To assess the properties of NSC-like C17.2 cells, we compared the properties of these cells with those reported for other NSC populations identified by a variety of different investigators using biological assays, microarray analysis, RT-PCR, and immunocytochemistry. We show that C17.2 cells differ significantly from other NSCs and cerebellar granule cell precursors, from which they were derived. In particular, they secrete additional growth factors and cytokines, express markers that distinguish them from other progenitor populations, and do not maintain karyotypic stability. Our results provide a caution on extrapolating results from C17.2 to other nonimmortalized stem cell populations and provide an explanation for some of the dramatic effects that are seen with C17.2 transplants but not with other cells. We suggest that, while C17.2 cells can illustrate many fundamental aspects of neural biology and are useful in their own right, their unique properties cannot be generalized.

A cultural renaissance: in vitro cell biology embraces three-dimensional context

Increasingly, researchers are recognizing the limitations of two-dimensional (2-D), monolayer cell culture and embracing more realistic three-dimensional (3-D) cell culture systems. Currently, 3-D culture techniques are being employed by neuroscientists to grow cells from the central nervous system. From this work, it has become clear that 3-D cell culture offers a more realistic milieu in which the functional properties of neurons can be observed and manipulated in a manner that is not possible in vivo. The implications of this technical renaissance in cell culture for both clinical and basic neuroscience are significant and far-reaching.

Cognitive reserve and the neurobiology of cognitive aging

A hypothetical construct of "cognitive reserve" is widely used to explain how, in the face of neurodegenerative changes that are similar in nature and extent, individuals vary considerably in the severity of cognitive aging and clinical dementia. Intelligence, education and occupational level are believed to be major active components of cognitive reserve. Here, we summarize the main features of cognitive aging and their neuropathological correlates. We describe the neurobiology of cognitive aging and conclude that perturbations of neural health attributable to oxidative stress and inflammatory processes alone are insufficient to distinguish cognitive aging from Alzheimer's disease. We introduce the concept of cognitive reserve and illustrate its utility in explaining individual differences in cognitive aging. Structural and functional brain imaging studies suggest plausible neural substrates of cognitive reserve, probably involving processes that support neuroplasticity in the aging brain. The cognitive reserve hypothesis conforms with reported associations between early and mid life lifestyle choices, early education, lifelong dietary habit, leisure pursuits and the retention of late life mental ability.

Neural stem cells redefined: a FACS perspective

Using the generally accepted ontogenetic definition, neural stem cells (NSCs) are characterized as undifferentiated cells originating from the neuroectoderm that have the capacity both to perpetually self-renew without differentiating and to generate multiple types of lineage-restricted progenitors (LRP). LRPs can themselves undergo limited self-renewal, then ultimately differentiate into highly specialized cells that compose the nervous system. However, this physiologically delimited definition of NSCs has been increasingly blurred in the current state of the field, as the great majority of studies have retrospectively inferred the existence of NSCs based on their deferred functional capability rather than prospectively identifying the actual cells that created the outcome. Further complicating the matter is the use of a wide variety of neuroepithelial or neurosphere preparations as a source of putative NSCs, without due consideration that these preparations are themselves composed of heterogeneous populations of both NSCs and LRPs. This article focuses on recent attempts using FACS strategies to prospectively isolate NSCs from different types of LRPs as they appear in vivo and reveals the contrasting differences among these populations at molecular, phenotypic, and functional levels. Thus, the strategies presented here provide a framework for more precise studies of NSC and LRP cell biology in the future.

Cytokines and the aging brain – what we don't know might help us

Cognitive aspects of aging represent a grave challenge for our societal circumstances as members of the baby-boom generation spiral toward a collective 'senior moment'. In addition, age-related changes in the CNS can contribute to motor deficits and other somatic aberrations. Inflammation and its regulation by cytokines have been connected to many aspects of aging, and mechanisms addressed here provide a rationale for this. Nevertheless, a role for cytokines in normal aging of the human brain has not been confirmed, and it seems to be possible to ameliorate both cognitive decline and cytokine elevation via lifestyle choices. So ignorance of the brain should not prohibit development of successful strategies for delaying or avoiding neurological deficits.

Motor and cognitive recovery induced by bone marrow stem cells grafted to striatum and hippocampus of impaired aged rats: functional and therapeutic considerations

Impairments in motor coordination and cognition in normal and pathological aging are often accompanied by structural changes, that is, loss of synapses and neurons. Also, it has been shown recently that bone marrow stem cells can give origin to cells of different tissues, including neural cells. Given the therapeutic implications of increasing health and functional possibilities in the aged brain, we have tested the effects of rat femur bone marrow stem cells (rBMSCs) grafting to the striatum hippocampus of aged rats with motor or cognitive deficits, respectively. Bone marrow cells were transduced with an adenovirus driving the expression of green fluorescence protein (GFP) and other classic stains to determine their migration, engraftment, differentiation, and associated behavioral recovery. Five weeks after it, control and grafted rats were re-evaluated with the Morris Water Maze test, Passive avoidance, open-field, motor coordination, and Marshall tests and perfused. Brains were processed and analyzed for fluorescent protein expression. GFP was detected in cells with some differentiation degree into neural-like cells. Their exact phenotype is yet to be determined. A significant functional recovery was observed 6 weeks after grafting, suggesting a trophic interaction between rBMSCs and the aged/dystrophic host brain, or with the host brain progenitor cells and/or by increasing the number of functional cells at striatum or hippocampus, suggesting that the aging brain keeps its functional plasticity as well as that BMSCs are interesting candidates for cell replacement therapies in neurodegenerative disorders.