Prospects for Neural Stem Cell Therapy of Alzheimer Disease Thorsten Gorba, Sarah Harper, and P. Joseph Mee

Abstract  Alzheimer disease (AD) is an incurable, degenerative, and terminal disease. Stem cellular therapeutics has been considered as offering the potential for possible intervention or cure. There is, however, an underlining complexity of AD in terms of its diversity in clinical presentation together with uncertainty over the molecular events associated with its onset. Neural stem cells cultured in vitro as neurospheres or adherent cultures may offer potential cellular resources. Nevertheless, AD with its heterogeneity in presentation and diffuse pathology remains a challenging cellular therapeutic target. Keywords  Neural stem cells • Alzheimer disease • Neurospheres • b-Amyloid neurodegeneration

1  Introduction Alzheimer disease (AD) is an incurable, degenerative, and terminal disease first described by Alois Alzheimer in 1906 [1]. Patients with AD can be categorized as either those with early-onset (familial) AD or, more commonly, late-onset (non­ familial) AD. Early-onset AD is caused in the majority through mutations in the amyloid precursor protein (APP) and accounts for less than 5% of cases. Late-onset AD is most often diagnosed in people older than 65 years of age, with the earliest symptoms sometimes mistaken as being part of the natural aging process. Typically these early symptoms often include short-term memory loss and clumsiness. For the late-onset forms of the disease there is no definitive cause, but there are a number of T. Gorba and P.J. Mee (*) Stem Cell Sciences UK Ltd., Minerva Building 250, Babraham Research Campus, Cambridge,  CB22 3AT, UK e-mail: [email protected]; [email protected] K. Appasani and R.K. Appasani (eds.), Stem Cells & Regenerative Medicine, Stem Cell Biology and Regenerative Medicine, DOI 10.1007/978-1-60761-860-7_20, © Springer Science+Business Media, LLC 2011

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risk factors, most notably age. The risk of Alzheimer disease doubles above the age of 65 years, and by the age of 85 years there is a 50% risk of having the disease (http://www.alz.org/alzheimers_disease_causes_risk_factors.asp). Other risk factors include having a previous head injury, having a family member with AD, cardiovascular disease, and apolipoprotein (Apo) allele status (see later discussion). AD is typically diagnosed via the use of standardized behavioral assessments and cognitive tests. Diagnosis of AD can be assisted via medical imaging to help exclude other cerebral pathology. Much effort has gone into the development of better in vivo imaging of the abnormal b-amyloid deposits by the use of Pittsburgh compound B positron emission tomography as part of the diagnosis [2]. Confirmation of AD occurs at post-mortem by histologic examination of brain tissue [3]. Although there are many common symptoms, each Alzheimer patient can manifest the condition in many different ways. In general, symptoms proceed from early-stage dementia to advanced dementia and death. Symptoms of advanced disease include irritability, aggression, confusion, mood swings, language breakdown, long-term memory loss, and withdrawal [4]. Prognosis for any individual patient is difficult to assess due to differences in the extent of the disease at diagnosis. However, life expectancy following diagnosis is approximately 7 years [5]. Death is associated with an eventual accumulation of a generalized functional loss and is usually caused by some indirect effect on the weakened body such as pneumonia. Autopsy reveals a characteristic loss of neurons and synapses resulting in ­degeneration in temporal and parietal lobes as well as parts of the frontal cortex and cingulate gyrus [3]. AD is a great social and economic burden [6]. The main caregiver is often the spouse or a close relative, often suffering considerable self-sacrifice and expense. The direct and indirect costs of caring for Alzheimer patients can be considerable [7, 8], and it has been estimated that the United States spends $100 billion each year on AD-associated costs [6].

2  The Biology of Alzheimer Disease The progressive cognitive decline seen in AD is characterized by the loss of synapses, the formation of neurofibrillary tangles, and the deposition of neuritic plaques composed of aggregated b-amyloid (Ab) in the neocortex and the limbic system [9, 10]. Synaptic loss during the course of Alzheimer disease occurs early in the progression of the disease and in two phases. The first involves loss of plasticity, and the second involves aberrant sprouting and neuritic disorganization, which leads to neurodegeneration. This precedes the neuronal loss that is due to plaques and tangle formation. Apoe4 is currently the only validated risk factor for late-onset (nonfamilial) Alzheimer disease (for review see ref. 11). Apoe is a protein required for the catabolism of triglyceride-rich lipoproteins and is specified by three possible alleles, Apoe2, Apoe3, and Apoe4. Apoe2 is associated with type III hyperlipo­proteinemia.

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Apoe3 is the neutral form with no associated risk factors for disease (55% of the population is homozygous for e3). Having two Apoe4 alleles (1%–2% of the population) is associated with 20 times increased risk of developing the late-onset, nonfamilial form of AD. How these two facts are related was unknown until recently, when was postulated that Apoe enhances the proteolytic breakdown of b-amyloid and the e4 isoform is less efficient at catalyzing the reaction than the other isoforms, potentially leading to increased deposition of plaques [12]. One of the first hypotheses put forward for the causes of Alzheimer disease was the cholinergic hypothesis. This was based on the fact that there is degeneration of the cholinergic neurons in the basal forebrain in patients with AD. These cholinergic neurons provide widespread innervations to the cortex and play a role in various cognitive functions, including memory. The loss of these neurons causes cognitive impairment. This led to the development of drugs that target the cholinergic system, the best-known of these being donepezil (Aricept). This drug inhibits the breakdown of acetylcholine by inhibiting the acetylcholinesterase and thus relies on there being sufficient cholinergic neurons remaining for the drug to act on. In fact there have been disappointing results for donepezil, with only modest improvements in cognition and no improvement in quality of life [13]. More recently research into causes of AD and treatments has focused on Ab and tau protein. Ab is a peptide of 39–43 amino acids and is the major constituent of senile plaques that are found in the aged brain and that are a hallmark of the AD brain. Ab is produced by sequential cleavage of APP, a protein present in all neuronal membranes and whose role is not clear. Cleavage of APP first by b-secretase produces a truncated APP still anchored into the cell membrane. Subsequent cleavage with g-secretase cleaves within the membrane, releasing the soluble Ab peptide. g-Secretase can cleave at Val711 or Ile713 to produce Ab1–42 or Ab1–40, respectively. Of the two forms, Ab1–40 is the more common, but Ab1–42 is more fibrillogenic and associated with early-onset AD. Some cases of early onset AD are linked to specific mutations around the b- and g-secretase cleavage sites—for example, the Swedish APP670/671 and London APP717 mutations [14–16]. Generally these mutations increase the amount of Ab peptides produced or the proportion of the longer Ab1–42, which is more likely to aggregate and is more toxic than the shorter Ab1–40. The second major hallmark of AD is the intracellular accumulation of microtubule-associated protein (MAP)–associated hyperphosphorylated tau. The “tau hypothesis” suggests that AD is driven by neurofibrillary tangles that arise as a result of either excess phosphorylation or a reduction in dephosphorylation. Tau was first isolated as a protein that copurifies with tubulin and promotes microtubule formation in vitro. Microtubules are key regulators of neuronal morphology via formation of axonal and dendritic processes (for review see ref. 17). They play a crucial role in both maintaining structure and in cellular trafficking, especially of mitochondria, synaptic vesicle proteins, ion channels, and receptors to and from presynaptic and postsynaptic sites. Synapses are particularly vulnerable to impairments in transport, and any blockages in transport can lead to malfunctions in synaptic transmission and ultimately synaptic degeneration—one of the early signs of AD.

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Oligomers of tau form into pre-tangles that assemble into insoluble filaments and then into tangles. The phosphorylation state of tau plays a key role in its affinity for both tubulin and for signaling molecules and thus could affect both microtubule dynamics and downstream signaling [18]. Hyperphosphorylated tau isolated from AD brain has a lower microtubule-promoting activity in vitro and sequesters normal tau, MAP1, and MAP2, causing the inhibition of assembly and the promotion of disassembly. This depletion of normal microtubules and presence of abnormal microtubules are likely to impair microtubule-based transport, and this will have major implications for the health of the cell. How Ab and tau are related in AD is still being debated. Unlike the situation with Ab, where there are known mutations associated with familial AD, there are no direct genetic links between tau and AD; mutations in tau are associated with frontotemporal dementia but not AD [19–21]. It has been postulated that excess Ab is the causative agent, and this event is upstream of tangle formation; however, it is not clear how excess Ab could lead to tau aggregation. The development of new medicines for Alzheimer disease requires the development of disease-relevant models, both in vitro and in animal models. AD is a disease that develops over decades, and therefore trying to model this in a culture dish over a period of days or weeks or in the much shorter lifespans of small-animal models remains challenging. Initial in  vitro models used in AD research were primitive and involved adding high concentrations of Ab peptides to cultured ­neurons. Initially, fresh peptides were added, but more recently peptides have been incubated at 37°C to induce aggregation similar to what is seen in vivo. These studies, however, used concentrations of peptides in the high-micromolar range, and in some cases the concentration was potentially high enough to cause cell death by preventing exchange of gases and nutrients rather than having a direct biologic effect. More recently these models have been used to look for subtler changes, for example, the effects of Ab on synaptic biology [22]. In vivo most research has centered on developing transgenic mouse models; however simpler organisms, such as Caenorhabditis elegans, Drosophila (for review see ref. 23), and zebrafish have also been used, which have distinct advantages over more complex rodent or primate models. In particular, they have a much shorter development and lifespan than higher vertebrates, making them attractive as experimental model systems. These model organisms possess homologs of genes involved in both the amyloid pathway and tau, and in addition these can be easily deleted and replaced with the human or mutated forms. Zebrafish can have genes deleted or modified by injection of the morpholino antisense oligonucleotides, mRNA, or transgenes and is small enough to be grown in 96-well plates, allowing relatively high throughput screening to be carried out on a whole (vertebrate) animal. Their translucent embryos allow imaging of disease progression at both cellular and subcellular levels. Compounds can be added directly to the water and are absorbed through the skin, and a variety of readouts can be measured, including altered mobility and changes in fluorescence. In a recent study, Paquet et  al. [24] successfully generated zebrafish that overexpress fluorescently labeled human tau P301L, a mutated form of human tau linked to frontotemporal dementia. The ­animals were

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used for compound screening, which resulted in the discovery of AR-534, a novel GSK-3b inhibitor, showing that it is possible to successfully screen for active drugs using a whole-animal model. The homolog of APP in Drosophila is Appl, but it does not contain the peptide Ab. However, deletions of Appl do cause defects in locomotor behavior, a phenotype that can be rescued by expressing the human APP [25]. Expression of the toxic Ab1–42 in Drosophila leads to diffuse extracellular amyloid, impaired olfactory associative learning, and neurodegeneration [26]. Drosophila also has a homolog of presenilin, and mutations in this protein cause phenotypes similar to notch mutants. Other components of the presenilin complex, including Aph1, nicastrin, and Pen-2, are also present in Drosophila. Another key molecule associated with AD, tau, has also been reported in Drosophila [27]. Overexpression of human tau in Drosophila sensory neurons causes abnormalities, including swelling and axonal degeneration [28]. Thus, all the key proteins implicated in AD are present in the fly and can be studied and modified using the advanced genetics available in this system. Despite the experimental advantages of these model organisms, there is a desire to have mammalian models that would allow the study of the consequences of specific mutations on higher-order brain function. The creation of transgenic animals that show all of the pathology of AD (Ab deposits, neurofibrillary tangles, neurodegeneration, and neuroinflammation) is essential for both our understanding of the disease progression and pathology and for the evaluation of novel therapeutic agents. There are no naturally occurring small-animal models of Alzheimer disease. The first transgenic mice were developed expressing the entire human APP gene, human APP751, Ab, or the C-terminal fragment of APP. All of these models showed only mild neuropathologic changes and few or no Ab deposits. Subsequently, mice were created that overexpressed mutant forms of human APP, and these did show age-dependent, AD-like pathology [29, 30]. The discovery of presenilin as a component of the g-secretase complex spurred the creation of a number of transgenic mouse lines. In spite of the fact that mutations associated with PS1 are associated with a form of familial AD [31], transgenic mice expressing either wild-type or mutated PS1 failed to develop substantial AD pathology. Breeding of the PS1 mice with the APP mice created animals with accelerated neuropathology [32]. The PDAPP mouse model expresses the human APP717 under the PDGF b-subunit promoter and has neuropathologic features characteristic of those observed in Alzheimer disease. Specifically, these include amyloid plaques, dystrophic neurites, activated glia, and loss of synapses in the hippocampus and frontal cortex, two regions of the brain that are particularly affected in Alzheimer disease [33]. The development of tau transgenic animals has confirmed the connection between tau and synaptic loss. Mice expressing P301S human tau [34] show hippocampal ­synaptic loss prior to the formation of neurofibrillary tangles. Loss of synaptic proteins can be detected as young as 3 months of age, and evaluation of the brains at 6  months (prior to neuronal loss and neurofibrillary tangle formation) showed impairments in synaptic transmission, presynaptic function and long-term potentiation in comparison with wild-type controls. For a more extensive review of relevant transgenic mouse models of human AD see Woodruff-Pak [35].

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3  Neural Stem Cells The overall encouraging outcomes of clinical trials in which human fetal ­mesencephalic tissue was transplanted into Parkinson disease patients [36, 37], together with the rapid pace of progress in the stem cell field, have raised awareness and expectations for future stem cell transplantation therapies for the treatment of Alzheimer disease. However, there are no reports of clinical trials using fetal brain tissue or stem cell transplants in AD patients. The reason for this mostly likely lies in the underlining complexity of AD in terms of its diversity in clinical presentation and uncertainty over the molecular events associated with its onset. Compared to the well-defined loss of ventral midbrain dopaminergic neurons in Parkinson disease, for example, the pathology of AD is diffuse, affecting multiple neuronal subtypes in different brain regions, leading to debate over which neuronal cell type would be the best to use in clinical trials. Nevertheless, stem cell research continues to be a major driver in the search for an AD cellular therapeutic. Somatic stem cells, for example, neural stem cells, are self-renewing, multipotential cells with the developmental capacity to give rise to all major cell types of a particular tissue, as opposed to progenitor cells, which are committed and restricted to a specific lineage fate. The three principal cell types into which multipotent neural stem cells can develop in vivo and in vitro are neurons, astrocytes, and oligodendrocytes. The development of enzymatic single-cell suspension methods of the fetal brain, initially used for the generation of primary neuronal and mixed glial cultures, enabled the breakthrough discovery that neural stem cells (NSCs) can be isolated from fetal or adult rodent central nervous system tissue and expanded as free-floating cell spheroids called “neurospheres” in the presence of growth factors [38–40]. Soon thereafter, long-term neurosphere NSC cultures were reported from the human fetal brain [41–44]. The neurosphere culture system takes advantage of the ability of NSCs to avoid anoikis and grow anchorage independently, whereas other differentiated cells and committed progenitors die off without attachment. This, together with the action of epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2) on stem cell proliferation, results over time in NSCenriched culture. It was suggested that for human neurosphere cultures, besides EGF and FGF-2, the addition of leukemia inhibitory factor further enhances their expansion [43]. The neurosphere system has proven invaluable in exploring NSC biology. The sphere cultures are heterogeneous, however, containing differentiating glial and neuronal cells in the center, surrounded by nestin-positive progenitors and NSC [45]. Significant enrichment of sphere-initiating NSCs in neurosphere ­cultures was achieved by positive selection with the prominin/CD133 cell surface marker during the isolation process [44]. Subsequently, the LeX/ssea-1 surface protein was suggested as another marker to enrich for NSC before the generation of neurosphere cultures [46]. The establishment of long-term, symmetrically self-renewing, adherent NSC cultures from both rodent and human central nervous system in the presence of EGF and FGF-2 has reduced the heterogeneity of cultured neural cells even further [47–49].

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The homogeneity of the adherent cultures also allows for meaningful global ­expression analysis of unimmortalized NSCs. Adherent NSCs display diagnostic profiles of neurogenic radial glia NSCs, the main source of cortical neurons during embryonic brain development [50, 51]. Although the existence of dividing cells in the adult brain was first demonstrated more than 40 years ago [52], it was not until much more recently that the existence of neural stem cells and the occurrence of neurogenesis in the adult mammalian brain, including human, were widely accepted and the prospective adult astroglial-like NSC was described in detail [53, 54]. Two main observations made in AD patients have led to the hypothesis that defects in NSCs and subsequent neurogenesis might be involved in the progression of the disease. First, odor identification is pathologically affected in AD patients, and even healthy individuals with the Apoe4 allele showed impairment compared with allele-negative controls [55, 56]. Second, the hippocampal formation is one of the regions in the AD brain that is most heavily burdened with amyloid plaques. Notably, the two recognized regions of adult neurogenesis are the subventricular zone (SVZ), replenishing the neurons of the olfactory bulb, and the dentate gyrus of the hippocampus, in which neurogenesis is suggested to be important for memory tasks that are impaired in AD [57, 58]. Therefore, an area of intense research effort, with conflicting results, concerns how soluble sAPP and Ab affect proliferation and differentiation of neural stem cells and adult neurogenesis. An early in  vitro study indicated that purified soluble forms of APP promoted the proliferation of NSCs rather than inhibiting it [59]. This principal finding was confirmed by experiments in  vivo, which showed that sAPP binds to EGFresponsive NSCs in the SVZ of the adult brain and acts as cofactor to stimulate the proliferation of these cells [60, 61]. However, other researchers reported that sAPP induced differentiation of human NSC into astrocyes and reduced the number of generated neurons, presumably mediated by the gp130 and notch signaling pathways [62, 63]. Other than for soluble APP, which appears to have attributes of a growth factor, in another in vitro study neurogenic effects of Ab peptide on hippocampal and striatal NSCs were also demonstrated. This activity was carried by Ab42 and not Ab40 and by oligomers rather than fibrils [64]. To further examine this subject, the rate of neurogenesis in numerous transgenic mouse AD models was investigated, and the results so far have been inconsistent. Initially two studies using APPSwe single-transgenic mouse lines reported decreased neurogenesis in the aged hippocampus [65, 66], whereas with a single-transgenic, double Swedish and Indiana APP mutant model a twofold increase in neurogenesis was found [67]. Ermini et  al. [68] demonstrated that the observed effects on neurogenesis are dependent on both the transgenic mouse model and the age of analysis. In singletransgenic APP23 mice overexpressing APPSwe at very high levels (sevenfold over endogenous APP) they found a significant increase in neurogenesis compared to controls at the age of 25 months, which could be interpreted as a compensatory response to neuronal cell death in the hippocampus. In contrast, double-transgenic, 8-month-old APP/PS1 mice exhibited decreased neurogenesis. Crucially, by crossing these mice with a nestin-GFP reporter strain, they demonstrated that this deficit already occurs at the level of quiescent astrocyte-like adult stem cells and

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not only through diminishing of neuronal differentiation from NSCs. Suggested mechanisms for the reduced neurogenesis from NSCs in AD transgenic mice include alterations of the gp130 and notch pathways in APP23 mice and increased BMP4 and reduced noggin expression levels in APP/PS1 mice [62, 63, 69, 70]. Of interest, triple-transgenic 3× Tg-AD mice, which harbor mutant genes for APP, presenilin-1, and tau, the mouse model with the best-known manifestation of cognitive decline, also had an impairment in hippocampal neurogenesis, which occurred earlier in females than in males, reflecting the higher prevalence of AD in women than in men [71–73]. There are very few publications describing the utility of NSCs after transplantation into transgenic mouse AD models. The group of Kiminobu Sugaya, whose research into the gliogenic effects of APP on NSCs was described earlier, reported that treatment with the cholinesterase inhibitor phenserine, known to reduce APP levels in  vitro and in  vivo, significantly increased the neuronal differentiation of implanted human NSCs in the hippocampus and cortex of APP23 mice [69]. This opens up a strategy in which pharmaceutical reduction of APP levels could improve neuronal replacement approaches with transplantation of NSCs. However, examples of acute brain injuries or other neurodegenerative diseases have shown that neuroreplacement is not necessarily required for therapeutic effects of NSC transplantation, which are instead mediated by growth factor secretion or immunomodulation. Indeed, a recent study demonstrated that NSCs transplanted into 3× Tg AD mice rescued spatial learning and memory deficits via a growth factor secretion bystander effect [74]. Consistent with the Sugaya group’s findings, only a small percentage of the transplanted NSCs differentiated into neurons, but growth factors secreted from the graft improved cognition via stimulating the formation of hippocampal synapses. Brain-derived neurotrophic factor (BDNF) was identified as playing a key role in this process. BDNF levels are decreased in brain and cerebrospinal fluid of patients with AD [75]. The major source of growth factor production secreted into the cerebrospinal fluid and therefore available to nourish NSCs in the SVZ are the epithelial cells of the choroid plexus, made up of modified ependymal cells, and it has therefore been hypothesized that aging and thinning of the choroid plexus epithelium concurrent with a declining growth factor secretion may be an underlying cause of neurodegenerative diseases, including AD [76–79].

4  Future Directions/Conclusions The social and economic impacts of AD disease will continue to drive research and development activities into cellular therapeutic approaches to finding a cure. This will only be possible with a continuing effort to study and understand the molecular and cellular defects that lead to the disease. Progress in neural stem cell research is offering greater understanding and better-tuned cellular resources for potential ­cellular therapeutics. Nevertheless, AD with its heterogeneity in presentation and diffuse pathology remains a challenging cellular therapeutic target. Despite this, the

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stem cell therapeutic research related to AD will continue to yield many insights and resources that in the short term could be used for drug-screening strategies with a longer-term view to cellular therapeutic strategies. This work was supported by the EU Sixth Research Framework Project NEUROscreen (LSHB-CT-2007/037766)

References 1. Amaducci, L. (1996) Alzheimer’s original patient. Science 274, 328. 2. Weiner, M.W. (2009) Editorial: Imaging and Biomarkers Will be Used for Detection and Monitoring Progression of Early Alzheimer’s Disease. J. Nutr Health Aging 13, 332. 3. Duyckaerts, C., Delatour, B. and Potier, M.C. (2009) Classification and basic pathology of Alzheimer disease. Acta Neuropathol. 118, 5–36. 4. Voisin, T. and Vellas, B. (2009) Diagnosis and treatment of patients with severe Alzheimer’s disease. Drugs Aging 26, 135–144. 5. Molsa, P.K., Marttila, R.J. and Rinne, U.K. (1986) Survival and cause of death in Alzheimer’s disease and multi-infarct dementia. Acta Neurol. Scand. 74, 103–107. 6. Meek, P.D., McKeithan, K. and Schumock, G.T. (1998) Economic considerations in Alzheimer’s disease. Pharmacotherapy 18, 68–73; discussion 79-82. 7. Murray, J., Schneider, J., Banerjee, S., et al. (1999) EUROCARE: a cross-national study of co-resident spouse carers for people with Alzheimer’s disease: II-A qualitative analysis of the experience of caregiving. Int. J. Geriatr. Psychiatry 14, 662–667. 8. Schneider, J., Murray, J., Banerjee, S., et al. (1999) EUROCARE: a cross-national study of co-resident spouse carers for people with Alzheimer’s disease: I-Factors associated with carer burden. Int. J. Geriatr. Psychiatry 14, 651–661. 9. Gearing, M., Mirra, S.S., Hedreen, J.C., et al. (1995) The Consortium to Establish a Registry for Alzheimer’s Disease (CERAD). Part X. Neuropathology confirmation of the clinical diagnosis of Alzheimer’s disease. Neurology 45, 461–466. 10. Terry, R.D., Masliah, E., Salmon, D.P., et al. (1991) Physical basis of cognitive alterations in Alzheimer’s disease: synapse loss is the major correlate of cognitive impairment. Ann. Neurol. 30, 572–580. 11. Bu, G. (2009) Apolipoprotein E and its receptors in Alzheimer’s disease: pathways, pathogenesis and therapy. Nat. Rev. Neurosci. 10, 333–344. 12. Jiang, Q., Lee, C.Y., Mandrekar, S., et al. (2008) ApoE promotes the proteolytic degradation of Abeta. Neuron 58, 681–693. 13. Steele, L.S. and Glazier, R.H. (1999) Is donepezil effective for treating Alzheimer’s disease? Can. Fam. Physician 45, 917–919. 14. Mullan, M., Crawford, F., Axelman, K., et  al. (1992) A pathogenic mutation for probable Alzheimer’s disease in the APP gene at the N-terminus of beta-amyloid. Nat. Genet. 1, 345–347. 15. Goate, A. (2006) Segregation of a missense mutation in the amyloid beta-protein precursor gene with familial Alzheimer’s disease. J. Alzheimers Dis. 9, 341–347. 16. Goate, A., Chartier-Harlin, M.C., Mullan, M., et al. (1991) Segregation of a missense mutation in the amyloid precursor protein gene with familial Alzheimer’s disease. Nature 349, 704–706. 17. Gendron, T.F. and Petrucelli, L. (2009) The role of tau in neurodegeneration. Mol. Neurodegener. 4, 13. 18. Amniai, L., Barbier, P., Sillen, A., et al. (2009) Alzheimer disease specific phosphoepitopes of Tau interfere with assembly of tubulin but not binding to microtubules. FASEB J. 23, 1146–1152. 19. Goedert, M., Ghetti, B., Spillantini, M.G. (2000) Tau gene mutations in frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). Their relevance for ­understanding the neurogenerative process. Ann. NY Acad. Sci. 920, 74–83.

346

T. Gorba et al.

20. Spillantini, M.G. and Goedert, M. (2000) Tau mutations in familial frontotemporal dementia. Brain 123, 857–859. 21. Spillantini, M.G., Van Swieten, J.C. and Goedert, M. (2000) Tau gene mutations in frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). Neurogenetics 2, 193–205. 22. Cappai, R. and Barnham, K.J. (2008) Delineating the mechanism of Alzheimer’s disease A beta peptide neurotoxicity. Neurochem. Res. 33, 526–532. 23. Sang, T.K. and Jackson, G.R. (2005) Drosophila models of neurodegenerative disease. NeuroRx 2, 438–446. 24. Paquet, D., Bhat, R., Sydow, A., et al. (2009) A zebrafish model of tauopathy allows in vivo imaging of neuronal cell death and drug evaluation. J. Clin. Invest. 119, 1382–1395. 25. Luo, L., Tully, T. and White, K. (1992) Human amyloid precursor protein ameliorates ­behavioral deficit of flies deleted for Appl gene. Neuron 9, 595–605. 26. Iijima, K., Liu, H.P., Chiang, A.S., et al. (2004) Dissecting the pathological effects of human Abeta40 and Abeta42 in Drosophila: a potential model for Alzheimer’s disease. Proc. Natl. Acad. Sci. USA. 101, 6623–6628. 27. Heidary, G. and Fortini, M.E. (2001) Identification and characterization of the Drosophila tau homolog. Mech. Dev. 108, 171–178. 28. Williams, D.W., Tyrer, M. and Shepherd, D. (2000) Tau and tau reporters disrupt central ­projections of sensory neurons in Drosophila. J. Comp. Neurol. 428, 630–640. 29. Games, D., Adams, D., Alessandrini, R., et  al. (1995) Alzheimer-type neuropathology in transgenic mice overexpressing V717F beta-amyloid precursor protein. Nature 373, 523–527. 30. Hsiao, K.K., Borchelt, D.R., Olson, K., et al. (1995) Age-related CNS disorder and early death in transgenic FVB/N mice overexpressing Alzheimer amyloid precursor proteins. Neuron 15, 1203–1218. 31. Sherrington, R., Rogaev, E.I., Liang, Y., et  al. (1995) Cloning of a gene bearing missense mutations in early-onset familial Alzheimer’s disease. Nature 375, 754–760. 32. Borchelt, D.R., Ratovitski, T., van Lare, J., et al. (1997) Accelerated amyloid deposition in the brains of transgenic mice coexpressing mutant presenilin 1 and amyloid precursor proteins. Neuron 19, 939–945. 33. Tanzi, R.E. (1995) A promising animal model of alzheimer’s disease N. Engl. J. Med. 332, 1512–1513. 34. Yoshiyama,Y., Higuchi, M., Zhang, B., et al. (2007) Synapse loss and microglial activation precede tangles in a P301S tauopathy mouse model. Neuron 53, 337–351. 35. Woodruff-Pak, D.S. (2008) Animal models of Alzheimer’s disease: therapeutic implications. J. Alzheimers Dis. 15, 507–521. 36. Kordower, J.H., Freeman, T.B., Snow, B.J., et al. (1995) Neuropathological evidence of graft survival and striatal reinnervation after the transplantation of fetal mesencephalic tissue in a patient with Parkinson’s disease. N. Engl. J. Med. 332, 1118–1124. 37. Lindvall, O. (1997) Neural transplantation: a hope for patients with Parkinson’s disease. Neuroreport 8, iii–x. 38. Reynolds, B.A., Tetzlaff, W. and Weiss, S. (1992) A multipotent EGF-responsive striatal embryonic progenitor cell produces neurons and astrocytes. J. Neurosci. 12, 4565–4574. 39. Reynolds, B.A. and Weiss, S. (1992) Generation of neurons and astrocytes from isolated cells of the adult mammalian central nervous system. Science 255, 1707–1710. 40. Weiss, S., Dunne, C., Hewson, J., et al. (1996) Multipotent CNS stem cells are present in the adult mammalian spinal cord and ventricular neuroaxis. J. Neurosci. 16, 7599–7609. 41. Svendsen, C.N., ter Borg, M.G., Armstrong, R.J., et al. (1998) A new method for the rapid and long term growth of human neural precursor cells. J. Neurosci. Methods 85, 141–152. 42. Vescovi, A.L., Parati, E.A., Gritti, A., et  al. (1999) Isolation and cloning of multipotential stem cells from the embryonic human CNS and establishment of transplantable human neural stem cell lines by epigenetic stimulation. Exp. Neurol. 156, 71–83.

Prospects for Neural Stem Cell Therapy of Alzheimer Disease

347

43. Carpenter, M.K., Cui, X., Hu, Z.Y., et al. (1999) In vitro expansion of a multipotent population of human neural progenitor cells. Exp. Neurol. 158, 265–278. 44. Uchida, N., Buck, D.W., He, D., et  al. (2000) Direct isolation of human central nervous ­system stem cells. Proc. Natl. Acad. Sci. USA. 97. 14720–14725. 45. Campos, L.S. (2004) Neurospheres: insights into neural stem cell biology. J Neurosci. Res. 78, 761–769. 46. Capela, A. and Temple, S. (2002) LeX/ssea-1 is expressed by adult mouse CNS stem cells, identifying them as nonependymal. Neuron 35, 865–875. 47. Conti, L., Pollard, S.M., Gorba, T., et al. (2005) Niche-independent symmetrical self-renewal of a mammalian tissue stem cell. PLoS Biol. 3, e283. 48. Pollard, S.M., Conti, L., Sun, Y., et al. (2006) Adherent neural stem (NS) cells from fetal and adult forebrain. Cereb. Cortex 16, Suppl 1, i112–i120. 49. Sun, Y., Pollard, S., Conti, L., et  al. (2008) Long-term tripotent differentiation capacity of human neural stem (NS) cells in adherent culture. Mol. Cell. Neurosci. 38, 245–258. 50. Malatesta, P., Hartfuss, E. and Gotz M (2000) Isolation of radial glial cells by fluorescentactivated cell sorting reveals a neuronal lineage. Development 127, 5253–5263. 51. Noctor, S.C., Flint, A.C, Weissman, T.A., et al. (2001) Neurons derived from radial glial cells establish radial units in neocortex. Nature 409, 714–720. 52. Altman, J. and Das, G.D. (1966) Autoradiographic and histological studies of postnatal neurogenesis. I. A longitudinal investigation of the kinetics, migration and transformation of cells incorporating tritiated thymidine in neonate rats, with special reference to postnatal neurogenesis in some brain regions. J. Comp. Neurol. 126, 337–389. 53. Garcia-Verdugo, J.M., Doetsch, F., Wichterle, H., et al. (1998) Architecture and cell types of the adult subventricular zone: in search of the stem cells. J. Neurobiol. 36, 234–248. 54. Doetsch, F., Caille, I., Lim, D.A., et al. (1999) Subventricular zone astrocytes are neural stem cells in the adult mammalian brain. Cell 97, 703–716. 55. Serby, M, (1987) Olfactory deficits in Alzheimer’s disease. J. Neural. Transm. Suppl. 24, 69–77. 56. Murphy, C. (1999) Loss of olfactory function in dementing disease. Physiol. Behav. 66, 177–182. 57. van Praag, H., Schinder, A.F., Christie, B.R., et al. (2002) Functional neurogenesis in the adult hippocampus. Nature 415, 1030–1034. 58. Shors, T.J., Miesegaes, G., Beylin, A., et al. (2001) Neurogenesis in the adult is involved in the formation of trace memories. Nature 410, 372–376. 59. Hayashi, Y., Kashiwagi, K., Ohta, J., et  al. (1994) Alzheimer amyloid protein precursor enhances proliferation of neural stem cells from fetal rat brain. Biochem. Biophys. Res. Commun. 205, 936–943. 60. Caille, I., Allinquant, B., Dupont, E., et al. (2004) Soluble form of amyloid precursor protein regulates proliferation of progenitors in the adult subventricular zone. Development 131, 2173–2181. 61. Conti, L. and Cattaneo, E. (2005) Controlling neural stem cell division within the adult subventricular zone: an APPealing job. Trends Neurosci. 28, 57–59. 62. Kwak, Y.D., Brannen, C.L., Qu, T., et al. (2006) Amyloid precursor protein regulates differentiation of human neural stem cells. Stem Cells Dev. 15, 381–389. 63. Sugaya. K. (2008) Mechanism of glial differentiation of neural progenitor cells by amyloid precursor protein. Neurodegener. Dis. 5, 170–172. 64. Lopez-Toledano, M.A. and Shelanski, M.L. (2004) Neurogenic effect of beta-amyloid peptide in the development of neural stem cells. J. Neurosci. 24, 5439–5444. 65. Haughey, N.J., Nath, A., Chan, S.L., et al. (2002) Disruption of neurogenesis by amyloid betapeptide, and perturbed neural progenitor cell homeostasis, in models of Alzheimer’s disease. J. Neurochem. 83, 1509–1524. 66. Dong, H., Goico, B., Martin, M., et al. (2004) Modulation of hippocampal cell proliferation, memory, and amyloid plaque deposition in APPsw (Tg2576) mutant mice by isolation stress. Neuroscience 127, 601–609.

348

T. Gorba et al.

67. Jin, K., Galvan, V., Xie, L., et  al. (2004) Enhanced neurogenesis in Alzheimer’s disease transgenic (PDGF-APPSw,Ind) mice. Proc. Natl. Acad. Sci. USA. 101, 13363–13367. 68. Ermini, F.V., Grathwohl, S., Radde, R., et al. (2008) Neurogenesis and alterations of neural stem cells in mouse models of cerebral amyloidosis. Am. J. Pathol. 172, 1520–1528. 69. Marutle, A., Ohmitsu, M., Nilbratt, M., et al. (2007) Modulation of human neural stem cell differentiation in Alzheimer (APP23) transgenic mice by phenserine. Proc. Natl. Acad. Sci. USA. 104, 12506–12511. 70. Tang, J., Song, M., Wang, Y., et al. (2009) Noggin and BMP4 co-modulate adult hippocampal neurogenesis in the APP(swe)/PS1(DeltaE9) transgenic mouse model of Alzheimer’s disease. Biochem. Biophys. Res. Commun. 385, 341–345. 71. Oddo, S., Caccamo, A., Shepherd, J.D., et al. (2003) Triple-transgenic model of Alzheimer’s disease with plaques and tangles: intracellular Abeta and synaptic dysfunction. Neuron 39, 409–421. 72. Billings, L.M., Oddo, S., Green, K.N., et al. (2005) Intraneuronal Abeta causes the onset of early Alzheimer’s disease-related cognitive deficits in transgenic mice. Neuron 45, 675–688. 73. Rodriguez, J.J., Jones, V.C., Tabuchi, M., et  al. (2008) Impaired adult neurogenesis in the dentate gyrus of a triple transgenic mouse model of Alzheimer’s disease. PLoS One 3, e2935. 74. Blurton-Jones, M., Kitazawa, M., Martinez-Coria, H., et al. (2009) Neural stem cells improve cognition via BDNF in a transgenic model of Alzheimer disease. Proc. Natl. Acad. Sci. USA. 106(32), 13594–13599. 75. Peng, S., Wuu, J., Mufson, E.J., et al. (2005) Precursor form of brain-derived neurotrophic factor and mature brain-derived neurotrophic factor are decreased in the pre-clinical stages of Alzheimer’s disease. J. Neurochem. 93, 1412–1421. 76. Redzic, Z.B., Preston JE, Duncan JA, Chodobski A, Szmydynger-Chodobska J (2005) The choroid plexus-cerebrospinal fluid system: from development to aging. Curr. Top. Dev. Biol. 71, 1–52. 77. Stopa, E.G., Berzin, T.M., Kim, S., et al. (2001) Human choroid plexus growth factors: What are the implications for CSF dynamics in Alzheimer’s disease? Exp. Neurol. 167, 40–47. 78. Emerich, D.F., Skinner, S.J., Borlongan, C.V. et al. (2005) The choroid plexus in the rise, fall and repair of the brain. Bioessays 27, 262–274. 79. Emerich, D.F., Vasconcellos, A.V., Elliott RB., et  al. (2004) The choroid plexus: function, pathology and therapeutic potential of its transplantation. Expert Opin. Biol. Ther. 4, 1191–1201.