Abeta immunotherapy protects morphology and survival of adult-born neurons in doubly transgenic APP/PS1 mice

Differentiated Embryonic Neurospheres from Familial Alzheimer's Disease Model Show Innate Immune and Glial Cell Responses

Proteins involved in the Alzheimer's disease (AD), such as amyloid precursor protein (APP) and presenilin-1 (PS1), play critical roles in early development of the central nervous system (CNS), as well as in innate immune and glial cell responses. Familial AD is associated with the presence of APPswe and PS1dE9 mutations. However, it is still unknown whether these mutations cause deficits in CNS development of carriers. We studied genome-wide gene expression profiles of differentiated neural progenitor cells (NPCs) from wild-type and APPswe/PS1dE9 mouse embryo telencephalon. The occurrence of strong innate immune and glial cell responses in APPswe/PS1dE9 neurospheres mainly involves microglial activation, inflammatory mediators and chemokines. APPswe/PS1dE9 neurospheres augmented up to 100-fold CCL12, CCL5, CCL3, C3, CX3CR1, TLR2 and TNF-alpha expression levels, when compared to WT neurospheres. Expression levels of the glia cell marker GFAP and microglia marker Iba-1 were up to 20-fold upregulated in APPswe/PS1dE9 neurospheres. The secretome of differentiated APPswe/PS1dE9 NPCs revealed enhanced chemoattraction of peripheral blood mononuclear cells. When evaluating the inferred protein interaction networks constructed from the array data, an improvement in astrocyte differentiation in APPswe/PS1dE9 neurospheres was evident in view of increased GFAP expression. Transgenic NPCs differentiated into neural phenotypes presented expression patterns of cytokine, glial cells, and inflammatory mediators characteristic of APPswe/PS1dE9 adult animals. Consequently, the neurogenic niche obtained from differentiation of embryonic APPswe/PS1dE9 neurospheres spontaneously presents several alterations observed in adult AD brains. Finally, our data strengthen pathophysiological hypotheses that propose an early neurodevelopmental origin for familial AD.

Optimal therapeutic conditions for the neural stem cell-based management of ischemic stroke: a systematic review and network meta-analysis based on animal studies

BACKGROUND

In order to promote the clinical translation of preclinical findings, it is imperative to identify the most optimal therapeutic conditions and adopt them for further animal and human studies. This study aimed to fully explore the optimal conditions for neural stem cell (NSC)-based ischemic stroke treatment based on animal studies.

METHODS

The PubMed, Ovid-Embase, and Web of Science databases were searched in December 2021. The screening of search results, extraction of relevant data, and evaluation of study quality were performed independently by two reviewers.

RESULTS

In total, 52 studies were included for data analysis. Traditional meta-analysis showed that NSCs significantly reduced the modified neurological severity score (mNSS) and volume of cerebral infarct in animal models of ischemic stroke. Network meta-analysis showed that allogeneic embryonic tissue was the best source of NSCs. Further, intracerebral transplantation was the most optimal route of NSC transplantation, and the acute phase was the most suitable stage for intervention. The optimal number of NSCs for transplantation was 1-5×10⁵ in mouse models and 1×10⁶ or 1.8×10⁶ in rat models.

CONCLUSIONS

We systematically explored the therapeutic strategy of NSCs in ischemic stroke, but additional research is required to develop optimal therapeutic strategies based on NSCs. Moreover, it is necessary to further improve and standardize the design, implementation, measuring standards, and reporting of animal-based studies to promote the development of better animal experiments and clinical research.

Does Impairment of Adult Neurogenesis Contribute to Pathophysiology of Alzheimer's Disease? A Still Open Question

Adult hippocampal neurogenesis is a physiological mechanism contributing to hippocampal memory formation. Several studies associated altered hippocampal neurogenesis with aging and Alzheimer's disease (AD). However, whether amyloid-β protein (Aβ)/tau accumulation impairs adult hippocampal neurogenesis and, consequently, the hippocampal circuitry, involved in memory formation, or altered neurogenesis is an epiphenomenon of AD neuropathology contributing negligibly to the AD phenotype, is, especially in humans, still debated. The detrimental effects of Aβ/tau on synaptic function and neuronal viability have been clearly addressed both in in vitro and in vivo experimental models. Until some years ago, studies carried out on in vitro models investigating the action of Aβ/tau on proliferation and differentiation of hippocampal neural stem cells led to contrasting results, mainly due to discrepancies arising from different experimental conditions (e.g., different cellular/animal models, different Aβ and/or tau isoforms, concentrations, and/or aggregation profiles). To date, studies investigating in situ adult hippocampal neurogenesis indicate severe impairment in most of transgenic AD mice; this impairment precedes by several months cognitive dysfunction. Using experimental tools, which only became available in the last few years, research in humans indicated that hippocampal neurogenesis is altered in cognitive declined individuals affected by either mild cognitive impairment or AD as well as in normal cognitive elderly with a significant inverse relationship between the number of newly formed neurons and cognitive impairment. However, despite that such information is available, the question whether impaired neurogenesis contributes to AD pathogenesis or is a mere consequence of Aβ/pTau accumulation is not definitively answered. Herein, we attempted to shed light on this complex and very intriguing topic by reviewing relevant literature on impairment of adult neurogenesis in mouse models of AD and in AD patients analyzing the temporal relationship between the occurrence of altered neurogenesis and the appearance of AD hallmarks and cognitive dysfunctions.

Nanoliposomes as a Therapeutic Tool for Alzheimer's Disease

The accumulation of extracellular amyloid-beta (Aβ), denoted as senile plaques, and intracellular neurofibrillary tangles (formed by hyperphosphorylated Tau protein) in the brain are two major neuropathological hallmarks of Alzheimer's disease (AD). The current and most accepted hypothesis proposes that the oligomerization of Aβ peptides triggers the polymerization and accumulation of amyloid, which leads to the senile plaques. Several strategies have been reported to target Aβ oligomerization/polymerization. Since it is thought that Aβ levels in the brain and peripheral blood maintain equilibrium, it has been hypothesized that enhancing peripheral clearance (by shifting this equilibrium towards the blood) might reduce Aβ levels in the brain, known as the sink effect. This process has been reported to be effective, showing a reduction in Aβ burden in the brain as a consequence of the peripheral reduction of Aβ levels. Nanoparticles (NPs) may have difficulty crossing the blood-brain barrier (BBB), initially due to their size. It is not clear whether particles in the range of 50-100 nm should be able to cross the BBB without being specifically modified for it. Despite the size limitation of crossing the BBB, several NP derivatives may be proposed as therapeutic tools. The purpose of this review is to summarize some therapeutic approaches based on nanoliposomes using two complementary examples: First, unilamellar nanoliposomes containing Aβ generic ligands, such as sphingolipids, gangliosides or curcumin, or some sphingolipid bound to the binding domain of ApoE; and second, nanoliposomes containing monoclonal antibodies against Aβ. Following similar rationale NPs of poly(lactide-co-glycolide)-poly (ethylene glycol) conjugated with curcumin-derivate (PLGA-PEG-B6/Cur) were reported to improve the spatial learning and memory capability of APP/PS1 mice, compared with native curcumin treatment. Also, some new nanostructures such as exosomes have been proposed as a putative therapeutic and prevention strategies of AD. Although the unquestionable interest of this issue is beyond the scope of this review article. The potential mechanisms and significance of nanoliposome therapies for AD, which are still are in clinical trials, will be discussed.

Neurite orientation dispersion and density imaging reveals white matter and hippocampal microstructure changes produced by Interleukin-6 in the TgCRND8 mouse model of amyloidosis

Extracellular β-amyloid (Aβ) plaque deposits and inflammatory immune activation are thought to alter various aspects of tissue microstructure, such as extracellular free water, fractional anisotropy and diffusivity, as well as the density and geometric arrangement of axonal processes. Quantifying these microstructural changes in Alzheimer's disease and related neurodegenerative dementias could serve to monitor or predict disease course. In the present study we used high-field diffusion magnetic resonance imaging (dMRI) to investigate the effects of Aβ and inflammatory interleukin-6 (IL6), alone or in combination, on in vivo tissue microstructure in the TgCRND8 mouse model of Alzheimer's-type Aβ deposition. TgCRND8 and non-transgenic (nTg) mice expressing brain-targeted IL6 or enhanced glial fibrillary protein (EGFP controls) were scanned at 8 months of age using a 2-shell, 54-gradient direction dMRI sequence at 11.1 T. Images were processed using the diffusion tensor imaging (DTI) model or the neurite orientation dispersion and density imaging (NODDI) model. DTI and NODDI processing in TgCRND8 mice revealed a microstructure pattern in white matter (WM) and hippocampus consistent with radial and longitudinal diffusivity deficits along with an increase in density and geometric complexity of axonal and dendritic processes. This included reduced FA, mean, axial and radial diffusivity, and increased orientation dispersion (ODI) and intracellular volume fraction (ICVF) measured in WM and hippocampus. IL6 produced a 'protective-like' effect on WM FA in TgCRND8 mice, observed as an increased FA that counteracted a reduction in FA observed with endogenous Aβ production and accumulation. In addition, we found that ICVF and ODI had an inverse relationship with the functional connectome clustering coefficient. The relationship between NODDI and graph theory metrics suggests that currently unknown microstructure alterations in WM and hippocampus are associated with diminished functional network organization in the brain.

Vitamin D Improves Neurogenesis and Cognition in a Mouse Model of Alzheimer's Disease

The impairment of hippocampal neurogenesis at the early stages of Alzheimer’s disease (AD) is believed to support early cognitive decline. Converging studies sustain the idea that vitamin D might be linked to the pathophysiology of AD and to hippocampal neurogenesis. Nothing being known about the effects of vitamin D on hippocampal neurogenesis in AD, we assessed them in a mouse model of AD. In a previous study, we observed that dietary vitamin D supplementation in female AD-like mice reduced cognitive decline only when delivered during the symptomatic phase. With these data in hand, we wondered whether the consequences of vitamin D administration on hippocampal neurogenesis are stage-dependent. Male wild-type and transgenic AD-like mice (5XFAD model) were fed with a diet containing either no vitamin D (0VD) or a normal dose of vitamin D (NVD) or a high dose of vitamin D (HVD), from month 1 to month 6 (preventive arm) or from month 4 to month 9 (curative arm). Working memory was assessed using the Y-maze, while amyloid burden, astrocytosis, and neurogenesis were quantified using immunohistochemistry. In parallel, the effects of vitamin D on proliferation and differentiation were assayed on primary cultures of murine neural progenitor cells. Improved working memory and neurogenesis were observed when high vitamin D supplementation was administered during the early phases of the disease, while a normal dose of vitamin D increased neurogenesis during the late phases. Conversely, an early hypovitaminosis D increased the number of amyloid plaques in AD mice while a late hypovitaminosis D impaired neurogenesis in AD and WT mice. The observed in vivo vitamin D-associated increased neurogenesis was partially substantiated by an augmented in vitro proliferation but not an increased differentiation of neural progenitors into neurons. Finally, a sexual dimorphism was observed. Vitamin D supplementation improved the working memory of males and females, when delivered during the pre-symptomatic and symptomatic phases, respectively. Our study establishes that (i) neurogenesis is improved by vitamin D in a male mouse model of AD, in a time-dependent manner, and (ii) cognition is enhanced in a gender-associated way. Additional pre-clinical studies are required to further understand the gender- and time-specific mechanisms of action of vitamin D in AD. This may lead to an adaptation of vitamin D supplementation in relation to patient’s gender and age as well as to the stage of the disease.

Pathophysiology in the comorbidity of Bipolar Disorder and Alzheimer's Disease: pharmacological and stem cell approaches

Neuropsychiatric disorders involve various pathological mechanisms, resulting in neurodegeneration and brain atrophy. Neurodevelopmental processes have shown to be critical for the progression of those disorders, which are based on genetic and epigenetic mechanisms as well as on extrinsic factors. We review here common mechanisms underlying the comorbidity of Bipolar Disorders and Alzheimer's Disease, such as aberrant neurogenesis and neurotoxicity, reporting current therapeutic approaches. The understanding of these mechanisms precedes stem cell-based strategies as a new therapeutic possibility for treatment and prevention of Bipolar and Alzheimer's Disease progression. Taking into account the difficulty of studying the molecular basis of disease progression directly in patients, we also discuss the importance of stem cells for effective drug screening, modeling and treating psychiatric diseases, once in vitro differentiation of patient-induced pluripotent stem cells provides relevant information about embryonic origins, intracellular pathways and molecular mechanisms.

Dual roles of Aβ in proliferative processes in an amyloidogenic model of Alzheimer's disease

Alzheimer’s disease is a major neurodegenerative disorder that leads to severe cognitive deficits in the elderly population. Over the past two decades, multiple studies have focused on elucidating the causative factors underlying memory defects in Alzheimer’s patients. In this regard, new evidence linking Alzheimer’s disease-related pathology and neuronal stem cells suggests that hippocampal neurogenesis impairment is an important factor underlying these cognitive deficits. However, because of conflicting results, the impact of Aβ pathology on neurogenesis/gliogenesis remains unclear. Here, we investigated the effect of Aβ on neuronal and glial proliferation by using an APP/PS1 transgenic model and in vitro assays. Specifically, we showed that neurogenesis is affected early in the APP/PS1 hippocampus, as evidenced by a significant decrease in the proliferative activity due to a reduced number of both radial glia-like neural stem cells (type-1 cells) and intermediate progenitor cells (type-2 cells). Moreover, we demonstrated that soluble Aβ from APP/PS1 mice impairs neuronal cell proliferation using neurosphere cultures. On the other hand, we showed that oligomeric Aβ stimulates microglial proliferation, whereas no effect was observed on astrocytes. These findings indicate that Aβ has a differential effect on hippocampal proliferative cells by inhibiting neuronal proliferation and triggering the formation of microglial cells.

Effects of Neurotrophic Support and Amyloid-Targeted Combined Therapy on Adult Hippocampal Neurogenesis in a Transgenic Model of Alzheimer's Disease

Although it is recognized that multi-drug therapies may be necessary to combat AD, there is a paucity of preclinical proof of concept studies. We present a combination treatment paradigm, which temporally affects different aspects of Alzheimer's disease (AD)-like pathology, specifically Aβ-toxicity and neurogenesis. At early stages of AD-like pathology, in TgCRND8 mice, we found that combating Aβ pathology with scyllo-inositol ameliorated deficits in neurogenesis. Older TgCRND8 mice with established amyloid load had decreased progenitor cell proliferation and survival compared to non-transgenic mice, regardless of scyllo-inositol treatment. The prolonged exposure to Aβ-pathology leads to deficits in the neurogenic niche, thus targeting Aβ alone is insufficient to rescue neurogenesis. To support the neurogenic niche, we combined scyllo-inositol treatment with leteprinim potassium (neotrofin), the latter of which stimulates neurotrophin expression. We show that the combination treatment of scyllo-inositol and neotrofin enhances neuronal survival and differentiation. We propose this proof of concept combination therapy of targeting Aβ-pathology and neurotrophin deficits as a potential treatment for AD.

The Ever-Changing Morphology of Hippocampal Granule Neurons in Physiology and Pathology

Newborn neurons are continuously added to the hippocampal dentate gyrus throughout adulthood. In this review, we analyze the maturational stages that newborn granule neurons go through, with a focus on their unique morphological features during each stage under both physiological and pathological circumstances. In addition, the influence of deleterious (such as schizophrenia, stress, Alzheimer's disease, seizures, stroke, inflammation, dietary deficiencies, or the consumption of drugs of abuse or toxic substances) and neuroprotective (physical exercise and environmental enrichment) stimuli on the maturation of these cells will be examined. Finally, the regulation of this process by proteins involved in neurodegenerative and neurological disorders such as Glycogen synthase kinase 3β, Disrupted in Schizophrenia 1 (DISC-1), Glucocorticoid receptor, pro-inflammatory mediators, Presenilin-1, Amyloid precursor protein, Cyclin-dependent kinase 5 (CDK5), among others, will be evaluated. Given the recently acquired relevance of the dendritic branch as a functional synaptic unit required for memory storage, a full understanding of the morphological alterations observed in newborn neurons may have important consequences for the prevention and treatment of the cognitive and affective alterations that evolve in conjunction with impaired adult hippocampal neurogenesis.

Are Anxiety Disorders Associated with Accelerated Aging? A Focus on Neuroprogression

Anxiety disorders (AnxDs) are highly prevalent throughout the lifespan, with detrimental effects on daily-life functioning, somatic health, and quality of life. An emerging perspective suggested that AnxDs may be associated with accelerated aging. In this paper, we explored the association between AnxDs and hallmarks of accelerated aging, with a specific focus on neuroprogression. We reviewed animal and human findings that suggest an overlap between processes of impaired neurogenesis, neurodegeneration, structural, functional, molecular, and cellular modifications in AnxDs, and aging. Although this research is at an early stage, our review suggests a link between anxiety and accelerated aging across multiple processes involved in neuroprogression. Brain structural and functional changes that accompany normal aging were more pronounced in subjects with AnxDs than in coevals without AnxDs, including reduced grey matter density, white matter alterations, impaired functional connectivity of large-scale brain networks, and poorer cognitive performance. Similarly, molecular correlates of brain aging, including telomere shortening, Aβ accumulation, and immune-inflammatory and oxidative/nitrosative stress, were overrepresented in anxious subjects. No conclusions about causality or directionality between anxiety and accelerated aging can be drawn. Potential mechanisms of this association, limitations of the current research, and implications for treatments and future studies are discussed.

Differential proteomic and behavioral effects of long-term voluntary exercise in wild-type and APP-overexpressing transgenics

Physical exercise may provide protection against the cognitive decline and neuropathology associated with Alzheimer's disease, although the mechanisms are not clear. In the present study, APP/PSEN1 double-transgenic and wild-type mice were allowed unlimited voluntary exercise for 7months. Consistent with previous reports, wheel-running improved cognition in the double-transgenic mice. Interestingly, the average daily distance run was strongly correlated with spatial memory in the water maze in wild-type mice (r(2)=.959), but uncorrelated in transgenics (r(2)=.013). Proteomics analysis showed that sedentary transgenic mice differed significantly from sedentary wild-types with respect to proteins involved in synaptic transmission, cytoskeletal regulation, and neurogenesis. When given an opportunity to exercise, the transgenics' deficiencies in cytoskeletal regulation and neurogenesis largely normalized, but abnormal synaptic proteins did not change. In contrast, exercise enhanced proteins associated with cytoskeletal regulation, oxidative phosphorylation, and synaptic transmission in wild-type mice. Soluble and insoluble Aβ40 and Aβ42 levels were significantly decreased in both cortex and hippocampus of active transgenics, suggesting that this may have played a role in the cognitive improvement in APP/PSEN1 mice. β-secretase was significantly reduced in active APP/PSEN1 mice compared to sedentary controls, suggesting a mechanism for reduced Aβ. Taken together, these data illustrate that exercise improves memory in wild-type and APP-overexpressing mice in fundamentally different ways.

Multifunctional liposomes reduce brain β-amyloid burden and ameliorate memory impairment in Alzheimer's disease mouse models

Alzheimer's disease is characterized by the accumulation and deposition of plaques of β-amyloid (Aβ) peptide in the brain. Given its pivotal role, new therapies targeting Aβ are in demand. We rationally designed liposomes targeting the brain and promoting the disaggregation of Aβ assemblies and evaluated their efficiency in reducing the Aβ burden in Alzheimer's disease mouse models. Liposomes were bifunctionalized with a peptide derived from the apolipoprotein-E receptor-binding domain for blood-brain barrier targeting and with phosphatidic acid for Aβ binding. Bifunctionalized liposomes display the unique ability to hinder the formation of, and disaggregate, Aβ assemblies in vitro (EM experiments). Administration of bifunctionalized liposomes to APP/presenilin 1 transgenic mice (aged 10 months) for 3 weeks (three injections per week) decreased total brain-insoluble Aβ1-42 (-33%), assessed by ELISA, and the number and total area of plaques (-34%) detected histologically. Also, brain Aβ oligomers were reduced (-70.5%), as assessed by SDS-PAGE. Plaque reduction was confirmed in APP23 transgenic mice (aged 15 months) either histologically or by PET imaging with [(11)C]Pittsburgh compound B (PIB). The reduction of brain Aβ was associated with its increase in liver (+18%) and spleen (+20%). Notably, the novel-object recognition test showed that the treatment ameliorated mouse impaired memory. Finally, liposomes reached the brain in an intact form, as determined by confocal microscopy experiments with fluorescently labeled liposomes. These data suggest that bifunctionalized liposomes destabilize brain Aβ aggregates and promote peptide removal across the blood-brain barrier and its peripheral clearance. This all-in-one multitask therapeutic device can be considered as a candidate for the treatment of Alzheimer's disease.

Repeated intraperitoneal injections of liposomes containing phosphatidic acid and cardiolipin reduce amyloid-β levels in APP/PS1 transgenic mice

The accumulation of extracellular amyloid-beta (Aβ) peptide and intracellular neurofibrillary tangles in the brain are two major neuropathological hallmarks of Alzheimer's disease (AD). It is thought that an equilibrium exists between Aβ in the brain and in the peripheral blood and thus, it was hypothesized that shifting this equilibrium towards the blood by enhancing peripheral clearance might reduce Aβ levels in the brain: the 'sink effect'. We tested this hypothesis by intraperitoneally injecting APP/PS1 transgenic mice with small unilamellar vesicles containing either phosphatidic acid or cardiolipin over 3weeks. This treatment reduced significantly the amount of Aβ in the plasma and the brain levels of Aβ were lighter affected. Nevertheless, this dosing regimen did modulate tau phosphorylation and glycogen synthase kinase 3 activities in the brain, suggesting that the targeting of circulating Aβ may be therapeutically relevant in AD.

FROM THE CLINICAL EDITOR

Intraperitoneal injection of small unilamellar vesicles containing phosphatidic acid or cardiolipin significantly reduced the amount of amyloid-beta (Aß) peptide in the plasma in a rodent model. Brain levels of Aß were also affected - although to a lesser extent - suggesting that targeting of circulating Aß may be therapeutically relevant of Alzheimer's disease.

Amyloid-β peptide-specific DARPins as a novel class of potential therapeutics for Alzheimer disease

Passive immunization with anti-amyloid-β peptide (Aβ) antibodies is effective in animal models of Alzheimer disease. With the advent of efficient in vitro selection technologies, the novel class of designed ankyrin repeat proteins (DARPins) presents an attractive alternative to the immunoglobulin scaffold. DARPins are small and highly stable proteins with a compact modular architecture ideal for high affinity protein-protein interactions. In this report, we describe the selection, binding profile, and epitope analysis of Aβ-specific DARPins. We further showed their ability to delay Aβ aggregation and prevent Aβ-mediated neurotoxicity in vitro. To demonstrate their therapeutic potential in vivo, mono- and trivalent Aβ-specific DARPins (D23 and 3×D23) were infused intracerebroventricularly into the brains of 11-month-old Tg2576 mice over 4 weeks. Both D23 and 3×D23 treatments were shown to result in improved cognitive performance and reduced soluble Aβ levels. These findings demonstrate the therapeutic potential of Aβ-specific DARPins for the treatment of Alzheimer disease.

What is normal in normal aging? Effects of aging, amyloid and Alzheimer's disease on the cerebral cortex and the hippocampus

What can be expected in normal aging, and where does normal aging stop and pathological neurodegeneration begin? With the slow progression of age-related dementias such as Alzheimer's disease (AD), it is difficult to distinguish age-related changes from effects of undetected disease. We review recent research on changes of the cerebral cortex and the hippocampus in aging and the borders between normal aging and AD. We argue that prominent cortical reductions are evident in fronto-temporal regions in elderly even with low probability of AD, including regions overlapping the default mode network. Importantly, these regions show high levels of amyloid deposition in AD, and are both structurally and functionally vulnerable early in the disease. This normalcy-pathology homology is critical to understand, since aging itself is the major risk factor for sporadic AD. Thus, rather than necessarily reflecting early signs of disease, these changes may be part of normal aging, and may inform on why the aging brain is so much more susceptible to AD than is the younger brain. We suggest that regions characterized by a high degree of life-long plasticity are vulnerable to detrimental effects of normal aging, and that this age-vulnerability renders them more susceptible to additional, pathological AD-related changes. We conclude that it will be difficult to understand AD without understanding why it preferably affects older brains, and that we need a model that accounts for age-related changes in AD-vulnerable regions independently of AD-pathology.

What is normal in normal aging? Effects of aging, amyloid and Alzheimer's disease on the cerebral cortex and the hippocampus

What can be expected in normal aging, and where does normal aging stop and pathological neurodegeneration begin? With the slow progression of age-related dementias such as Alzheimer's disease (AD), it is difficult to distinguish age-related changes from effects of undetected disease. We review recent research on changes of the cerebral cortex and the hippocampus in aging and the borders between normal aging and AD. We argue that prominent cortical reductions are evident in fronto-temporal regions in elderly even with low probability of AD, including regions overlapping the default mode network. Importantly, these regions show high levels of amyloid deposition in AD, and are both structurally and functionally vulnerable early in the disease. This normalcy-pathology homology is critical to understand, since aging itself is the major risk factor for sporadic AD. Thus, rather than necessarily reflecting early signs of disease, these changes may be part of normal aging, and may inform on why the aging brain is so much more susceptible to AD than is the younger brain. We suggest that regions characterized by a high degree of life-long plasticity are vulnerable to detrimental effects of normal aging, and that this age-vulnerability renders them more susceptible to additional, pathological AD-related changes. We conclude that it will be difficult to understand AD without understanding why it preferably affects older brains, and that we need a model that accounts for age-related changes in AD-vulnerable regions independently of AD-pathology.

Pyroglutamate-Modified Amyloid Beta Peptides: Emerging Targets for Alzheimer´s Disease Immunotherapy

Extracellular and intraneuronal accumulation of amyloid-beta (Aβ) peptide aggregates in the brain has been hypothesized to play an important role in the neuropathology of Alzheimer’s Disease (AD). The main Aβ variants detected in the human brain are Aβ1-40 and Aβ1-42, however a significant proportion of AD brain Aβ consists also of N-terminal truncated species. Pyroglutamate-modified Aβ peptides have been demonstrated to be the predominant components among all N-terminal truncated Aβ species in AD brains and represent highly desirable and abundant therapeutic targets. The current review describes the properties and localization of two pyroglutamate-modified Aβ peptides, AβN3(pE) and AβN11(pE), in the brain. The role of glutaminyl cyclase (QC) in the formation of these peptides is also addressed. In addition, two potential therapeutic strategies, the inhibition of QC and immunotherapy approaches, and clinical trials aimed to target these important pathological Aβ species are reviewed.

Age-dependent neuroplasticity mechanisms in Alzheimer Tg2576 mice following modulation of brain amyloid-β levels

The objective of this study was to investigate the effects of modulating brain amyloid-β (Aβ) levels at different stages of amyloid pathology on synaptic function, inflammatory cell changes and hippocampal neurogenesis, i.e. processes perturbed in Alzheimer's disease (AD). Young (4- to 6-month-old) and older (15- to 18-month-old) APP(SWE) transgenic (Tg2576) mice were treated with the AD candidate drug (+)-phenserine for 16 consecutive days. We found significant reductions in insoluble Aβ1-42 levels in the cortices of both young and older transgenic mice, while significant reductions in soluble Aβ1-42 levels and insoluble Aβ1-40 levels were only found in animals aged 15-18 months. Autoradiography binding with the amyloid ligand Pittsburgh Compound B ((3)H-PIB) revealed a trend for reduced fibrillar Aβ deposition in the brains of older phenserine-treated Tg2576 mice. Phenserine treatment increased cortical synaptophysin levels in younger mice, while decreased interleukin-1β and increased monocyte chemoattractant protein-1 and tumor necrosis factor-alpha levels were detected in the cortices of older mice. The reduction in Aβ1-42 levels was associated with an increased number of bromodeoxyuridine-positive proliferating cells in the hippocampi of both young and older Tg2576 mice. To determine whether the increased cell proliferation was accompanied by increased neuronal production, the endogenous early neuronal marker doublecortin (DCX) was examined in the dentate gyrus (DG) using immunohistochemical detection. Although no changes in the total number of DCX(+)-expressing neurons were detected in the DG in Tg2576 mice at either age following (+)-phenserine treatment, dendritic arborization was increased in differentiating neurons in young Tg2576 mice. Collectively, these findings indicate that reducing Aβ1-42 levels in Tg2576 mice at an early pathological stage affects synaptic function by modulating the maturation and plasticity of newborn neurons in the brain. In contrast, lowering Aβ levels in Tg2576 mice when Aβ plaque pathology is prominent mainly alters the levels of proinflammatory cytokines and chemokines.

Cell and gene therapy in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurological disorder characterized by the aggregation of two proteins, amyloid-β and hyperphosphorylated tau, and by neuronal and synaptic loss. Although some drugs have been shown to slow the progression of the disease, at present no treatment has been developed that can stop or reverse the progression of the pathology. Recently, new therapeutic strategies have been proposed for the treatment of the disease. Among these, the development of stem cells and gene-modified cells is an especially promising therapeutic approach for AD. In this review we highlight the experimental and preclinical studies that have been focused on stem cell-based and gene-modified cell-based uses as potential therapies for AD. The potential clinical applications are also discussed.

Glycogen synthase kinase 3 inhibition promotes adult hippocampal neurogenesis in vitro and in vivo

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase originally identified as a regulator of glycogen metabolism but it also plays a pivotal role in numerous cellular functions, including differentiation, cell cycle regulation, and proliferation. The dentate gyrus of the hippocampus, together with the subventricular zone of the lateral ventricles, is one of the regions in which neurogenesis takes place in the adult brain. Here, using a chemical genetic approach that involves the use of several diverse inhibitors of GSK-3 as pharmacological tools, we show that inhibition of GSK-3 induces proliferation, migration, and differentiation of neural stem cells toward a neuronal phenotype in in vitro studies. Also, we demonstrate that inhibition of GSK-3 with the small molecule NP03112, called tideglusib, induces neurogenesis in the dentate gyrus of the hippocampus of adult rats. Taken together, our results suggest that GSK-3 should be considered as a new target molecule for modulating the production and integration of new neurons in the hippocampus as a treatment for neurodegenerative diseases or brain injury and, consequently, its inhibitors may represent new potential therapeutic drugs in neuroregenerative medicine.

Combination therapy prevents amyloid-dependent and -independent structural changes

Neuropathological features of Alzheimer's disease (AD) are recapitulated in transgenic mice expressing familial AD-causing mutations, but ectopic transgene overexpression makes it difficult to relate these abnormalities to disease pathogenesis. Alternatively, the APP/PS-1 double knock-in (DKI) mouse produces mutant amyloid precursor protein (APP) and presenilin-1 (PS-1) with normal levels and regulatory controls. Here, we investigated effects of amyloid on brain structure and neuroplasticity by vaccinating DKI mice with amyloid-β starting at 8 months of age. At 14 months, vaccination blocked cerebral amyloid deposition and its attendant microglial activation. Neuropil abnormalities were pronounced only within plaques, and included circumscribed loss and dysmorphology of axons, dendrites, terminals and spines. Blockade of amyloid deposition restored neuropil integrity. Amyloid removal did not rescue reductions in the hippocampal neural progenitor and neuroblast populations, but adding 1 month of voluntary exercise to amyloid-β vaccination markedly stimulated hippocampal neurogenesis. These results identify amyloid-dependent and -independent structural changes in the DKI mouse model of AD. Combining exercise with amyloid-directed immunotherapy produces greater restoration of brain structure and neuroplasticity than is achieved with either maneuver alone.

Synaptic changes in Alzheimer's disease and its models

Alzheimer's disease (AD) is a highly prevalent neurodegenerative disorder characterized by a progressive loss of cognition and the presence of two hallmark lesions, senile plaques (SP) and neurofibrillary tangles (NFT), which result from the accumulation and deposition of the β-amyloid peptide (Aβ) and the aggregation of hyperphosphorylated tau protein, respectively. Initially, it was thought that Aβ fibrils, which make up SP, were the root cause of the massive neurodegeneration usual found in AD brains. Over time, the longstanding emphasis on fibrillar Aβ deposits and neuronal death slowly gave way to a new paradigm involving soluble oligomeric forms of Aβ, which play a prominent role in triggering the cognitive deficits by specifically targeting synapses and disrupting synaptic signaling pathways. While this paradigm is widely accepted today in the AD field, the molecular details have not been fully elucidated. In this review, we address some of the important evidence, which has led to the Aβ oligomer-centric hypothesis as well as some of the key findings concerning the effects of Aβ oligomers on synapses at a morphological and functional level. Understanding how Aβ oligomers target synapses provides an important framework for ongoing AD research, which can lead to the development of successful therapeutic strategies designed to alter or perhaps reverse the course of the disease.

Effects of human intravenous immunoglobulin on amyloid pathology and neuroinflammation in a mouse model of Alzheimer's disease

BACKGROUND

Human intravenous immunoglobulin (hIVIG) preparation is indicated for treating primary immunodeficiency disorders associated with impaired humoral immunity. hIVIG is known for its anti-inflammatory properties and a decent safety profile. Therefore, by virtue of its constituent natural anti-amyloid beta antibodies and anti-inflammatory effects, hIVIG is deemed to mediate beneficial effects to patients of Alzheimer's disease (AD). Here, we set out to explore the effects of hIVIG in a mouse model of AD.

METHODS

We treated APP/PS1dE9 transgenic and wild-type mice with weekly injections of a high hIVIG dose (1 g/kg) or saline for 3 or 8 months. Treatment effect on brain amyloid pathology and microglial reactivity was assessed by ELISA, immunohistochemistry, RT-PCR, and confocal microscopy.

RESULTS

We found no evidence for reduction in Aβ pathology; instead 8 months of hIVIG treatment significantly increased soluble levels of Aβ40 and Aβ42. In addition, we noticed a significant reduction in CD45 and elevation of Iba-1 markers in specific sub-populations of microglial cells. Long-term hIVIG treatment also resulted in significant suppression of TNF-α and increase in doublecortin positive adult-born neurons in the dentate gyrus.

CONCLUSIONS

Our data indicate limited ability of hIVIG to impact amyloid burden but shows changes in microglia, pro-inflammatory gene expression, and neurogenic effects. Immunomodulation by hIVIG may account for its beneficial effect in AD patients.

Inhibition of microglial activation protects hippocampal neurogenesis and improves cognitive deficits in a transgenic mouse model for Alzheimer's disease

BACKGROUND

Activated microglia with macrophage-like functions invade and surround β-amyloid (Aβ) plaques in Alzheimer's disease (AD), possibly contributing to the turnover of Aβ, but they can also secrete proinflammatory factors that may be involved in the pathogenesis of AD. Microglia are known to modulate adult hippocampal neurogenesis.

OBJECTIVES/METHODS

To determine the role of microglia on neurogenesis in brains with Aβ pathology, we inhibited microglial activation with the tetracycline derivative minocycline in doubly transgenic mice expressing mutant human amyloid precursor protein (APP) and mutant human presenilin-1 (PS1).

RESULTS

Minocycline increased the survival of new dentate granule cells in APP/PS1 mice indicated by more BrdU+/NeuN+ cells as compared to vehicle-treated transgenic littermates, accompanied by improved behavioral performance in a hippocampus-dependent learning task. Both brain levels of Aβ and Aβ-related morphological deficits in the new neurons labeled with GFP-expressing retrovirus were unaffected in minocycline-treated mice.

CONCLUSIONS

These results suggest a role for microglia in Aβ-related functional deficits and in suppressing the survival of new neurons, and show that modulation of microglial function with minocycline can protect hippocampal neurogenesis in the presence of Aβ pathology.

Inflammation, mitochondria, and the inhibition of adult neurogenesis

The process of neurogenesis continues throughout life, with thousands of new neurons generated every day in the mammalian brain. Impairment of hippocampal neurogenesis has been suggested to be involved in neurodegenerative conditions, including the cognitive decline associated with aging, Alzheimer's disease, Parkinson's disease, and ionizing radiation. These neurodegenerative conditions are all characterized by proinflammatory changes and increased numbers of activated microglia. Activated microglia produce a variety of proinflammatory factors, including interleukin-6, tumor necrosis factor-α, reactive oxygen species, and nitric oxide, all of which are antineurogenic. These same factors have also been shown to suppress mitochondrial function, but the role of mitochondria in neurogenesis remains barely investigated. This brief review summarizes the findings of several studies that support a role for mitochondrial impairment as part of the mechanism of the reduction of neurogenesis associated with inflammation.

Neurogenesis in Alzheimer´s disease: a realistic alternative to neuronal degeneration?

Neural stem cells (NSC) are cells that have the capacity to generate multiple types of differentiated brain cells. In conditions in which there is a loss of key functional cell groups, such as neurons, inducing or introducing neural stem cells to replace the function of those cells that were lost during the disease has the greatest potential therapeutic applications. Indeed, the achievement of one of the main objectives of various investigations is already on the horizon for some conditions, such as Alzheimer's disease. It is not known whether impaired neurogenesis contributes to neuronal depletion and cognitive dysfunction in Alzheimer's disease (AD). The results of the different investigations are controversial; some studies have found that neurogenesis is increased in AD brains, but others have not.

Functional integration of new hippocampal neurons following insults to the adult brain is determined by characteristics of pathological environment

We have previously shown that following severe brain insults, chronic inflammation induced by lipopolysaccharide (LPS) injection, and status epilepticus, new dentate granule cells exhibit changes of excitatory and inhibitory synaptic drive indicating that they may mitigate the abnormal brain function. Major inflammatory changes in the environment encountering the new neurons were a common feature of these insults. Here, we have asked how the morphology and electrophysiology of new neurons are affected by a comparably mild pathology: repetitive seizures causing hyperexcitability but not inflammation. Rats were subjected to rapid kindling, i.e., 40 rapidly recurring, electrically-induced seizures, and subsequently exposed to stimulus-evoked seizures twice weekly. New granule cells were labeled 1 week after the initial insult with a retroviral vector encoding green fluorescent protein. After 6-8 weeks, new neurons were analyzed using confocal microscopy and whole-cell patch-clamp recordings. The new neurons exposed to the pathological environment exhibited only subtle changes in their location, orientation, dendritic arborizations, and spine morphology. In contrast to the more severe insults, the new neurons exposed to rapid kindling and stimulus-evoked seizures exhibited enhanced afferent excitatory synaptic drive which could suggest that the cells that had developed in this environment contributed to hyperexcitability. However, the new neurons showed concomitant reduction of intrinsic excitability which may counteract the propagation of this excitability to the target cells. This study provides further evidence that following insults to the adult brain, the pattern of synaptic alterations at afferent inputs to newly generated neurons is dependent on the characteristics of the pathological environment.

Perturbed cellular response to brain injury during aging

Old age is associated with an enhanced susceptibility to stroke and poor recovery from brain injury, but the cellular processes underlying these phenomena are only partly understood. Therefore, studying the basic mechanisms underlying structural and functional recovery after brain injury in aged subjects is of considerable clinical interest. Behavioral and cytological analyses of rodents that have undergone experimental injury show that: (a) behaviorally, aged rodents are more severely impaired by ischemia than are young animals, and older rodents also show diminished functional recovery; (b) compared to young animals, aged animals develop a larger infarct area, as well as a necrotic zone characterized by a higher rate of cellular degeneration and a larger number of apoptotic cells; (c) both astrocytes and macrophages are activated strongly and early following stroke in aged rodents; (d) in older animals, the premature, intense cytoproliferative activity following brain injury leads to the precipitous formation of growth-inhibiting scar tissue, a phenomenon amplified by the persistent expression of neurotoxic factors; (e) though the timing is altered, the regenerative capability of the brain is largely preserved in rats, at least into early old age. Whether endogenous neurogenesis contributes to spontaneous recovery after stroke has not yet been established. If neurogenesis from endogenous neuronal stem cells is to be used therapeutically, an individual approach will be required to assess the possible extent of neurogenic response as well as the possibilities to alter this response for functional improvement or prevention of further loss of brain function.

Cell number and timing of transplantation determine survival of human neural stem cell grafts in stroke-damaged rat brain

Neural stem cells (NSCs) derived from human fetal striatum and transplanted as neurospheres survive in stroke-damaged striatum, migrate from the implantation site, and differentiate into mature neurons. Here, we investigated how various steps of neurogenesis are affected by intrastriatal transplantation of human NSCs at different time points after stroke and with different numbers of cells in each implant. Rats were subjected to middle cerebral artery occlusion and then received intrastriatal transplants of NSCs. Transplantation shortly after stroke (48 hours) resulted in better cell survival than did transplantation 6 weeks after stroke, but the delayed transplantation did not influence the magnitude of migration, neuronal differentiation, and cell proliferation in the grafts. Transplanting greater numbers of grafted NSCs did not result in a greater number of surviving cells or increased neuronal differentiation. A substantial number of activated microglia was observed at 48 hours after the insult in the injured striatum, but reached maximum levels 1 to 6 weeks after stroke. Our findings show that the best survival of grafted human NSCs in stroke-damaged brain requires optimum numbers of cells to be transplanted in the early poststroke phase, before the inflammatory response is established. These findings, therefore, have direct clinical implications.

Cucumber mosaic virus as the expression system for a potential vaccine against Alzheimer's disease

A primary therapeutic goal in Alzheimer's disease (AD) is to reduce the quantity of amyloid β protein (Aβ) present in the brain. To develop an effective, safe system for vaccination against Alzheimer's disease, the plant virus Cucumber mosaic virus (CMV) was engineered genetically to express Aβ-derived fragments that stimulate mainly humoral immune responses. Six chimeric constructs, bearing the Aβ1-15 or the Aβ4-15 sequence in positions 248, 392 or 529 of the CMV coat protein (CP) gene, were created. Viral products proved to be able to replicate in their natural host. However, only chimeric Aβ1-15-CMVs were detected by Aβ1-42 antiserum in Western blot analysis. Experimental evidence of Immunoelectron microscopy revealed a complete decoration of Aβ1-15-CMV(248) and Aβ1-15-CMV(392) following incubation with either anti-Aβ1-15 or anti-Aβ1-42 polyclonal antibodies. These two chimeric CMVs appear to be endowed with features making them possible candidates for vaccination against Alzheimer's disease.

Role of oxidant scavengers in the prevention of Ca²+ homeostasis disorders

A number of disorders, such as Alzheimer disease and diabetes mellitus, have in common the alteration of the redox balance, resulting in an increase in reactive oxygen species (ROS) generation that might lead to the development of apoptosis and cell death. It has long been known that ROS can significantly alter Ca²+ mobilization, an intracellular signal that is involved in the regulation of a wide variety of cellular functions. Cells have a limited capability to counteract the effects of oxidative stress, but evidence has been provided supporting the beneficial effects of exogenous ROS scavengers. Here, we review the effects of oxidative stress on intracellular Ca²+ homeostasis and the role of antioxidants in the prevention and treatment of disorders associated to abnormal Ca²+ mobilization induced by ROS.

Anti-PrPC monoclonal antibody infusion as a novel treatment for cognitive deficits in an Alzheimer's disease model mouse

BACKGROUND

Alzheimer's Disease (AD) is the most common of the conformational neurodegenerative disorders characterized by the conversion of a normal biological protein into a β-sheet-rich pathological isoform. In AD the normal soluble Aβ (sAβ) forms oligomers and fibrils which assemble into neuritic plaques. The most toxic form of Aβ is thought to be oligomeric. A recent study reveals the cellular prion protein, PrPC, to be a receptor for Aβ oligomers. Aβ oligomers suppress LTP signal in murine hippocampal slices but activity remains when pretreated with the PrP monoclonal anti-PrP antibody, 6D11. We hypothesized that targeting of PrPC to prevent Aβ oligomer-related cognitive deficits is a potentially novel therapeutic approach. APP/PS1 transgenic mice aged 8 months were intraperitoneally (i.p.) injected with 1 mg 6D11 for 5 days/week for 2 weeks. Two wild-type control groups were given either the same 6D11 injections or vehicle solution. Additional groups of APP/PS1 transgenic mice were given either i.p. injections of vehicle solution or the same dose of mouse IgG over the same period. The mice were then subjected to cognitive behavioral testing using a radial arm maze, over a period of 10 days. At the conclusion of behavioral testing, animals were sacrificed and brain tissue was analyzed biochemically or immunohistochemically for the levels of amyloid plaques, PrPC, synaptophysin, Aβ40/42 and Aβ oligomers.

RESULTS

Behavioral testing showed a marked decrease in errors in 6D11 treated APP/PS1 Tg mice compared with the non-6D11 treated Tg groups (p < 0.0001). 6D11 treated APP/PS1 Tg mice behaved the same as wild-type controls indicating a recovery in cognitive learning, even after this short term 6D11 treatment. Brain tissue analysis from both treated and vehicle treated APP/PS1 groups indicate no significant differences in amyloid plaque burden, Aβ40/42, PrPC or Aβ oligomer levels. 6D11 treated APP/PS1 Tg mice had significantly greater synaptophysin immunoreactivity in the dentate gyrus molecular layer of the hippocampus compared to vehicle treated APP/PS1 Tg mice (p < 0.05).

CONCLUSIONS

Even short term treatment with monoclonal antibodies such as 6D11 or other compounds which block the binding of Aβ oligomers to PrPC can be used to treat cognitive deficits in aged AD transgenic mice.

Anti-11[E]-pyroglutamate-modified amyloid β antibodies cross-react with other pathological Aβ species: relevance for immunotherapy

N-truncated/modified forms of amyloid beta (Aß) peptide are found in diffused and dense core plaques in Alzheimer's disease (AD) and Down's syndrome patients as well as animal models of AD, and represent highly desirable therapeutic targets. In the present study we have focused on N-truncated/modified Aβ peptide bearing amino-terminal pyroglutamate at position 11 (AβN11(pE)). We identified two B-cell epitopes recognized by rabbit anti-AβN11(pE) polyclonal antibodies. Interestingly, rabbit anti-AβN11(pE) polyclonal antibodies bound also to full-length Aβ1-42 and N-truncated/modified AβN3(pE), suggesting that the three peptides may share a common B-cell epitope. Importantly, rabbit anti-AβN11(pE) antibodies bound to naturally occurring Aβ aggregates present in brain samples from AD patients. These results are potentially important for developing novel immunogens for targeting N-truncated/modified Aβ aggregates as well, since the most commonly used immunogens in the majority of vaccine studies have been shown to induce antibodies that recognize the N-terminal immunodominant epitope (EFRH) of the full length Aβ, which is absent in N-amino truncated peptides.

Impaired orthotopic glioma growth and vascularization in transgenic mouse models of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia among the aging population and is characterized pathologically by the progressive intracerebral accumulation of beta-amyloid (Abeta) peptides and neurofibrillary tangles. The level of proangiogenic growth factors and inflammatory mediators with proangiogenic activity is known to be elevated in AD brains which has led to the supposition that the cerebrovasculature of AD patients is in a proangiogenic state. However, angiogenesis depends on the balance between proangiogenic and antiangiogenic factors and the brains of AD patients also show an accumulation of endostatin and Abeta peptides which have been shown to be antiangiogenic. To determine whether angiogenesis is compromised in the brains of two transgenic mouse models of AD overproducing Abeta peptides (Tg APPsw and Tg PS1/APPsw mice), we assessed the growth and vascularization of orthotopically implanted murine gliomas since they require a high degree of angiogenesis to sustain their growth. Our data reveal that intracranial tumor growth and angiogenesis is significantly reduced in Tg APPsw and Tg PS1/APPsw mice compared with their wild-type littermates. In addition, we show that Abeta inhibits the angiogenesis stimulated by glioma cells when cocultured with human brain microvascular cells on a Matrigel layer. Altogether our data suggest that the brain of transgenic mouse models of AD does not constitute a favorable environment to support neoangiogenesis and may explain why vascular insults synergistically precipitate the cognitive presentation of AD.

Memory impairment in transgenic Alzheimer mice requires cellular prion protein

Soluble oligomers of the amyloid-beta (Abeta) peptide are thought to play a key role in the pathophysiology of Alzheimer's disease (AD). Recently, we reported that synthetic Abeta oligomers bind to cellular prion protein (PrP(C)) and that this interaction is required for suppression of synaptic plasticity in hippocampal slices by oligomeric Abeta peptide. We hypothesized that PrP(C) is essential for the ability of brain-derived Abeta to suppress cognitive function. Here, we crossed familial AD transgenes encoding APPswe and PSen1DeltaE9 into Prnp-/- mice to examine the necessity of PrP(C) for AD-related phenotypes. Neither APP expression nor Abeta level is altered by PrP(C) absence in this transgenic AD model, and astrogliosis is unchanged. However, deletion of PrP(C) expression rescues 5-HT axonal degeneration, loss of synaptic markers, and early death in APPswe/PSen1DeltaE9 transgenic mice. The AD transgenic mice with intact PrP(C) expression exhibit deficits in spatial learning and memory. Mice lacking PrP(C), but containing Abeta plaque derived from APPswe/PSen1DeltaE9 transgenes, show no detectable impairment of spatial learning and memory. Thus, deletion of PrP(C) expression dissociates Abeta accumulation from behavioral impairment in these AD mice, with the cognitive deficits selectively requiring PrP(C).

Dendritic vulnerability in neurodegenerative disease: insights from analyses of cortical pyramidal neurons in transgenic mouse models

In neurodegenerative disorders, such as Alzheimer's disease, neuronal dendrites and dendritic spines undergo significant pathological changes. Because of the determinant role of these highly dynamic structures in signaling by individual neurons and ultimately in the functionality of neuronal networks that mediate cognitive functions, a detailed understanding of these changes is of paramount importance. Mutant murine models, such as the Tg2576 APP mutant mouse and the rTg4510 tau mutant mouse have been developed to provide insight into pathogenesis involving the abnormal production and aggregation of amyloid and tau proteins, because of the key role that these proteins play in neurodegenerative disease. This review showcases the multidimensional approach taken by our collaborative group to increase understanding of pathological mechanisms in neurodegenerative disease using these mouse models. This approach includes analyses of empirical 3D morphological and electrophysiological data acquired from frontal cortical pyramidal neurons using confocal laser scanning microscopy and whole-cell patch-clamp recording techniques, combined with computational modeling methodologies. These collaborative studies are designed to shed insight on the repercussions of dystrophic changes in neocortical neurons, define the cellular phenotype of differential neuronal vulnerability in relevant models of neurodegenerative disease, and provide a basis upon which to develop meaningful therapeutic strategies aimed at preventing, reversing, or compensating for neurodegenerative changes in dementia.

Neurogenesis in mouse models of Alzheimer's disease

The brains of the adult mouse and human possess neural stem cells (NSCs) that retain the capacity to generate new neurons through the process of neurogenesis. They share the same anatomical locations of stem cell niches in the brain, as well as the prominent feature of rostral migratory stream formed by neuroblasts migrating from the lateral ventricles towards the olfactory bulb. Therefore the mouse possesses some fundamental features that may qualify it as a relevant model for adult human neurogenesis. Adult born young hippocampal neurons in the mouse display the unique property of enhanced plasticity, and can integrate physically and functionally into existing neural circuits in the brain. Such crucial properties of neurogenesis may at least partially underlie the improved learning and memory functions observed in the mouse when hippocampal neurogenesis is augmented, leading to the suggestion that neurogenesis induction may be a novel therapeutic approach for diseases with cognitive impairments such as Alzheimer's disease (AD). Research towards this goal has benefited significantly from the use of AD mouse models to facilitate the understanding in the impact of AD pathology on neurogenesis. The present article reviews the growing body of controversial data on altered neurogenesis in mouse models of AD and attempts to assess their relative relevance to humans.

Stem cells in human neurodegenerative disorders--time for clinical translation?

Stem cell-based approaches have received much hype as potential treatments for neurodegenerative disorders. Indeed, transplantation of stem cells or their derivatives in animal models of neurodegenerative diseases can improve function by replacing the lost neurons and glial cells and by mediating remyelination, trophic actions, and modulation of inflammation. Endogenous neural stem cells are also potential therapeutic targets because they produce neurons and glial cells in response to injury and could be affected by the degenerative process. As we discuss here, however, significant hurdles remain before these findings can be responsibly translated to novel therapies. In particular, we need to better understand the mechanisms of action of stem cells after transplantation and learn how to control stem cell proliferation, survival, migration, and differentiation in the pathological environment.