Decreased proliferation of hippocampal progenitor cells in APPswe/PS1dE9 transgenic mice

Vascular senescence and leak are features of the early breakdown of the blood-brain barrier in Alzheimer's disease models

Alzheimer's disease (AD) is an age-related disease, with loss of integrity of the blood-brain barrier (BBB) being an early feature. Cellular senescence is one of the reported nine hallmarks of aging. Here, we show for the first time the presence of senescent cells in the vasculature in AD patients and mouse models of AD. Senescent endothelial cells and pericytes are present in APP/PS1 transgenic mice but not in wild-type littermates at the time of amyloid deposition. In vitro, senescent endothelial cells display altered VE-cadherin expression and loss of cell junction formation and increased permeability. Consistent with this, senescent endothelial cells in APP/PS1 mice are present at areas of vascular leak that have decreased claudin-5 and VE-cadherin expression confirming BBB breakdown. Furthermore, single cell sequencing of endothelial cells from APP/PS1 transgenic mice confirms that adhesion molecule pathways are among the most highly altered pathways in these cells. At the pre-plaque stage, the vasculature shows significant signs of breakdown, with a general loss of VE-cadherin, leakage within the microcirculation, and obvious pericyte perturbation. Although senescent vascular cells were not directly observed at sites of vascular leak, senescent cells were close to the leak area. Thus, we would suggest in AD that there is a progressive induction of senescence in constituents of the neurovascular unit contributing to an increasing loss of vascular integrity. Targeting the vasculature early in AD, either with senolytics or with drugs that improve the integrity of the BBB may be valid therapeutic strategies.

Beneficial effects of physical exercise and an orally active mGluR2/3 antagonist pro-drug on neurogenesis and behavior in an Alzheimer's amyloidosis model

Background

Modulation of physical activity represents an important intervention that may delay, slow, or prevent mild cognitive impairment (MCI) or dementia due to Alzheimer's disease (AD). One mechanism proposed to underlie the beneficial effect of physical exercise (PE) involves the apparent stimulation of adult hippocampal neurogenesis (AHN). BCI-838 is a pro-drug whose active metabolite BCI-632 is a negative allosteric modulator at group II metabotropic glutamate receptors (mGluR2/3). We previously demonstrated that administration of BCI-838 to a mouse model of brain accumulation of oligomeric AβE22Q (APP E693Q = "Dutch APP") reduced learning behavior impairment and anxiety, both of which are associated with the phenotype of Dutch APP mice.

Methods

3-month-old mice were administered BCI-838 and/or physical exercise for 1 month and then tested in novel object recognition, neurogenesis, and RNAseq.

Results

Here we show that (i) administration of BCI-838 and a combination of BCI-838 and PE enhanced AHN in a 4-month old mouse model of AD amyloid pathology (APP KM670/671NL /PSEN1 Δexon9= APP/PS1), (ii) administration of BCI-838 alone or with PE led to stimulation of AHN and improvement in recognition memory, (iii) the hippocampal dentate gyrus transcriptome of APP/PS1 mice following BCI-838 treatment showed up-regulation of brain-derived neurotrophic factor (BDNF), PIK3C2A of the PI3K-mTOR pathway, and metabotropic glutamate receptors, and down-regulation of EIF5A involved in modulation of mTOR activity by ketamine, and (iv) validation by qPCR of an association between increased BDNF levels and BCI-838 treatment.

Conclusion

Our study points to BCI-838 as a safe and orally active compound capable of mimicking the beneficial effect of PE on AHN and recognition memory in a mouse model of AD amyloid pathology.

Examination of Longitudinal Alterations in Alzheimer’s Disease-Related Neurogenesis in an APP/PS1 Transgenic Mouse Model, and the Effects of P33, a Putative Neuroprotective Agent Thereon

Neurogenesis plays a crucial role in cognitive processes. During aging and in Alzheimer’s disease (AD), altered neurogenesis and neuroinflammation are evident both in C57BL/6J, APP_Swe/PS1_dE9 (Tg) mice and humans. AD pathology may slow down upon drug treatment, for example, in a previous study of our group P33, a putative neuroprotective agent was found to exert advantageous effects on the elevated levels of APP, Aβ, and neuroinflammation. In the present study, we aimed to examine longitudinal alterations in neurogenesis, neuroinflammation and AD pathology in a transgenic (Tg) mouse model, and assessed the putative beneficial effects of long-term P33 treatment on AD-specific neurological alterations. Hippocampal cell proliferation and differentiation were significantly reduced between 8 and 12 months of age. Regarding neuroinflammation, significantly elevated astrogliosis and microglial activation were observed in 6- to 7-month-old Tg animals. The amounts of the molecules involved in the amyloidogenic pathway were altered from 4 months of age in Tg animals. P33-treatment led to significantly increased neurogenesis in 9-month-old animals. Our data support the hypothesis that altered neurogenesis may be a consequence of AD pathology. Based on our findings in the transgenic animal model, early pharmacological treatment before the manifestation of AD symptoms might ameliorate neurological decline.

Shati/Nat8l Overexpression Improves Cognitive Decline by Upregulating Neuronal Trophic Factor in Alzheimer's Disease Model Mice

Alzheimer's disease (AD) is a type of dementia characterized by the deposition of amyloid β, a causative protein of AD, in the brain. Shati/Nat8l, identified as a psychiatric disease related molecule, is a responsive enzyme of N-acetylaspartate (NAA) synthesis. In the hippocampi of AD patients and model mice, the NAA content and Shati/Nat8l expression were reported to be reduced. Having recently clarified the involvement of Shati/Nat8l in cognitive function, we examined the recovery effect of the hippocampal overexpression of Shati/Nat8l in AD model mice (5XFAD). Shati/Nat8l overexpression suppressed cognitive dysfunction without affecting the Aβ burden or number of NeuN-positive neurons. In addition, brain-derived neurotrophic factor mRNA was upregulated by Shati/Nat8l overexpression in 5XFAD mice. These results suggest that Shati/Nat8l overexpression prevents cognitive dysfunction in 5XFAD mice, indicating that Shati/Nat8l could be a therapeutic target for AD.

Functional Deficits of 5×FAD Neural Stem Cells Are Ameliorated by Glutathione Peroxidase 4

Alzheimer's disease (AD) is the most common cause of dementia affecting millions of people around the globe. Impaired neurogenesis is reported in AD as well as in AD animal models, although the underlying mechanism remains unclear. Elevated lipid peroxidation products are well-documented in AD. In current study, the role of lipid peroxidation on neural stem cell (NSCs) function is tested. Neural stem cells (NSCs) from 5×FAD mice, a widely used AD model with impaired neurogenesis, were observed to have increased levels of lipid reactive oxygen species compared to NSCs from control WT mice. 5×FAD NSCs exhibited altered differentiation potential as revealed by their propensity to differentiate into astrocytic lineage instead of neuronal lineage compared to WT NSCs. In addition, 5×FAD NSCs showed a reduced level of Gpx4, a key enzyme in reducing hydroperoxides in membrane lipids, and this reduction appeared to be caused by enhanced autophagy-lysosomal degradation of Gpx4 protein. To test if increasing Gpx4 could restore differentiation potential, NSCs from 5×FAD and Gpx4 double transgenic mice, i.e., 5×FAD/GPX4 mice were studied. Remarkably, upon differentiation, neuronal linage cells increased significantly in 5×FAD/GPX4 cultures compared to 5×FAD cultures. Taken together, the findings suggest that deficiency of lipid peroxidation defense contributes to functional decline of NSCs in AD.

Mitochondrial aldehyde dehydrogenase (ALDH2) rescues cardiac contractile dysfunction in an APP/PS1 murine model of Alzheimer's disease via inhibition of ACSL4-dependent ferroptosis

Alzheimer's disease (AD) is associated with high incidence of cardiovascular events but the mechanism remains elusive. Our previous study reveals a tight correlation between cardiac dysfunction and low mitochondrial aldehyde dehydrogenase (ALDH2) activity in elderly AD patients. In the present study we investigated the effect of ALDH2 overexpression on cardiac function in APP/PS1 mouse model of AD. Global ALDH2 transgenic mice were crossed with APP/PS1 mutant mice to generate the ALDH2-APP/PS1 mutant mice. Cognitive function, cardiac contractile, and morphological properties were assessed. We showed that APP/PS1 mice displayed significant cognitive deficit in Morris water maze test, myocardial ultrastructural, geometric (cardiac atrophy, interstitial fibrosis) and functional (reduced fractional shortening and cardiomyocyte contraction) anomalies along with oxidative stress, apoptosis, and inflammation in myocardium. ALDH2 transgene significantly attenuated or mitigated these anomalies. We also noted the markedly elevated levels of lipid peroxidation, the essential lipid peroxidation enzyme acyl-CoA synthetase long-chain family member 4 (ACSL4), the transcriptional regulator for ACLS4 special protein 1 (SP1) and ferroptosis, evidenced by elevated NCOA4, decreased GPx4, and SLC7A11 in myocardium of APP/PS1 mutant mice; these effects were nullified by ALDH2 transgene. In cardiomyocytes isolated from WT mice and in H9C2 myoblasts in vitro, application of Aβ (20 μM) decreased cell survival, compromised cardiomyocyte contractile function, and induced lipid peroxidation; ALDH2 transgene or activator Alda-1 rescued Aβ-induced deteriorating effects. ALDH2-induced protection against Aβ-induced lipid peroxidation was mimicked by the SP1 inhibitor tolfenamic acid (TA) or the ACSL4 inhibitor triacsin C (TC), and mitigated by the lipid peroxidation inducer 5-hydroxyeicosatetraenoic acid (5-HETE) or the ferroptosis inducer erastin. These results demonstrate an essential role for ALDH2 in AD-induced cardiac anomalies through regulation of lipid peroxidation and ferroptosis.

A Preclinical Model of Computerized Cognitive Training: Touchscreen Cognitive Testing Enhances Cognition and Hippocampal Cellular Plasticity in Wildtype and Alzheimer's Disease Mice

With the growing popularity of touchscreen cognitive testing in rodents, it is imperative to understand the fundamental effects exposure to this paradigm can have on the animals involved. In this study, we set out to assess hippocampal-dependant learning in the APP/PS1 mouse model of Alzheimer’s disease (AD) on two highly translatable touchscreen tasks – the Paired Associate Learning (PAL) task and the Trial Unique Non-Matching to Location (TUNL) task. Both of these tests are based on human tasks from the Cambridge Neuropsychological Test Automated Battery (CANTAB) and are sensitive to deficits in both mild cognitive impairment (MCI) and AD. Mice were assessed for deficits in PAL at 9–12 months of age, then on TUNL at 8–11 and 13–16 months. No cognitive deficits were evident in APP/PS1 mice at any age, contrary to previous reports using maze-based learning and memory tasks. We hypothesized that daily and long-term touchscreen training may have inadvertently acted as a cognitive enhancer. When touchscreen-tested mice were assessed on the Morris water maze, they showed improved task acquisition compared to naïve APP/PS1 mice and wild-type (WT) littermate controls. In addition, we show that touchscreen-trained WT and APP/PS1 mice show increased cell proliferation and immature neuron numbers in the dentate gyrus compared to behaviorally naïve WT and APP/PS1 mice. This result indicates that the touchscreen testing paradigm could improve cognitive performance, and/or mask an impairment, in experimental mouse models. This touchscreen-induced cognitive enhancement may involve increased neurogenesis, and possibly other forms of cellular plasticity. This is the first study to show increased numbers of proliferating cells and immature neurons in the hippocampus following touchscreen testing, and that touchscreen training can improve cognitive performance in maze-based spatial navigation tasks. This potential for touchscreen testing to induce cognitive enhancement, or other phenotypic shifts, in preclinical models should be considered in study design. Furthermore, touchscreen-mediated cognitive enhancement could have therapeutic implications for cognitive disorders.

Alkoxy glycerol enhanced activity of Oxyresveratrol in Alzheimer's disease by rescuing Tau protein

Alzheimer's disease perpetually demands enormous research on the development of effective treatment strategies. The present study aims to define the role of Oxyresveratrol (OXY) alone and in combination with Alkoxy glycerols (AKG) to reduce Tau protein level and improve the climbing behaviour of Drosophila fly models expressed with human-Tau protein. Oxyresveratrol, a polyphenolic stilbene, possesses a wide range of biological activities like antioxidant, anti-inflammatory, and neuroprotective effects. Nevertheless, chemical instability and low solubility of OXY in aqueous solutions reduce its bioavailability and hinder it from exerting neuroprotective activities. An inclusion complex of OXY with β- cyclodextrin (CD) (OXY-CD complex) was employed in the study for increased dissolution rate and oral availability of OXY. Fish oils and their derivatives have a plethora of applications in in vivo biological activities. Herein, we also remark on the role of AKG in reducing Tau protein level in flies by enhancing OXY-CD activity. Dietary supplementation of OXY-CD together with AKG improved the learning and memory abilities during the climbing assay in Tau flies. The study highlights OXY-CD and AKG as neuroprotective agents and put forward a plausible approach towards the increased permeability of pharmacological agents across the blood-brain barrier (BBB) for the central nervous system elicited by AKG.

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.

Leptin enhances adult neurogenesis and reduces pathological features in a transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most common dementia worldwide and is characterized by the presence of senile plaques by amyloid-beta (Aβ) and neurofibrillary tangles of hyperphosphorylated Tau protein. These changes lead to progressive neuronal degeneration and dysfunction, resulting in severe brain atrophy and cognitive deficits. With the discovery that neurogenesis persists in the adult mammalian brain, including brain regions affected by AD, studies of the use of neural stem cells (NSCs) for the treatment of neurodegenerative diseases to repair or prevent neuronal cell loss have increased. Here we demonstrate that leptin administration increases the neurogenic process in the dentate gyrus of the hippocampus as well as in the subventricular zone of lateral ventricles of adult and aged mice. Chronic treatment with leptin increased NSCs proliferation with significant effects on proliferation and differentiation of newborn cells. The expression of the long form of the leptin receptor, LepRb, was detected in the neurogenic niches by reverse qPCR and immunohistochemistry. Moreover, leptin modulated astrogliosis, microglial cell number and the formation of senile plaques. Additionally, leptin led to attenuation of Aβ-induced neurodegeneration and superoxide anion production as revealed by Fluoro-Jade B and dihydroethidium staining. Our study contributes to the understanding of the effects of leptin in the brain that may lead to the development of new therapies to treat Alzheimer's disease.

Adult hippocampal neurogenesis in Alzheimer's disease

New neurons are generated in the dentate gyrus of the adult brain throughout life. They incorporate in the granular cell layer of the dentate gyrus and integrate in the hippocampal circuitry. Increasing evidence suggests that new neurons play a role in learning and memory. In turn, a large body of evidence suggests that neurogenesis is impaired in Alzheimer's disease, contributing to memory deficits characterizing the disease. We outline here current knowledge about the biology of adult hippocampal neurogenesis and its function in learning and memory. In addition, we discuss evidence that neurogenesis is dysfunctional in Alzheimer's disease, address the controversy in the literature concerning the persistence of hippocampal neurogenesis in the adult and aging human brain, and evaluate the therapeutic potential of neurogenesis-based drug development for the treatment of cognitive deficits in Alzheimer's disease.

Harnessing neurogenesis in the adult brain-A role in type 2 diabetes mellitus and Alzheimer's disease

Some metabolic disorders, such as type 2 diabetes mellitus (T2DM) are risk factors for the development of cognitive deficits and Alzheimer's disease (AD). Epidemiological studies suggest that in people with T2DM, the risk of developing dementia is 2.5 times higher than that in the non-diabetic population. The signaling pathways that underlie the increased risk and facilitate cognitive deficits are not fully understood. In fact, the cause of memory deficits in AD is not fully elucidated. The dentate gyrus of the hippocampus plays an important role in memory formation. Hippocampal neurogenesis is the generation of new neurons and glia in the adult brain throughout life. New neurons incorporate in the granular cell layer of the dentate gyrus and play a role in learning and memory and hippocampal plasticity. A large body of studies suggests that hippocampal neurogenesis is impaired in mouse models of AD and T2DM. Recent evidence shows that hippocampal neurogenesis is also impaired in human patients exhibiting mild cognitive impairment or AD. This review discusses the role of hippocampal neurogenesis in the development of cognitive deficits and AD, and considers inflammatory and endothelial signaling pathways in T2DM that may compromise hippocampal neurogenesis and cognitive function, leading to AD.

Estradiol Replacement at the Critical Period Protects Hippocampal Neural Stem Cells to Improve Cognition in APP/PS1 Mice

It has been suggested that there is a critical window for estrogen replacement therapy (ERT) in postmenopausal women with Alzheimer’s disease (AD); however, supporting evidence is lacking. To address this issue, we investigated the effective period for estradiol (E2) treatment using a mouse model of AD. Four-month-old female APPswe/PSEN1dE9 (APP/PS1) mice were ovariectomized (OVX) and treated with E2 for 2 months starting at the age of 4 months (early period), 6 months (mid-period), or 8 months (late period). We then evaluated hippocampal neurogenesis, β-amyloid (Aβ) accumulation, telomerase activity, and hippocampal-dependent behavior. Compared to age-matched wild type mice, APP/PS1 mice with intact ovaries showed increased proliferation of hippocampal neural stem cells (NSCs) at 8 months of age and decreased proliferation of NSCs at 10 months of age; meanwhile, Aβ accumulation progressively increased with age, paralleling the reduced survival of immature neurons. OVX-induced depletion of E2 in APP/PS1 mice resulted in elevated Aβ levels accompanied by elevated p75 neurotrophin receptor (p75^NTR) expression and increased NSC proliferation at 6 months of age, which subsequently declined; accelerated reduction of immature neurons starting from 6 months of age, and reduced telomerase activity and worsened memory performance at 10 months of age. Treatment with E2 in the early period post-OVX, rather than in the mid or late period, abrogated these effects, and p75^NTR inhibition reduced the overproliferation of NSCs in 6-month-old OVX-APP/PS1 mice. Thus, E2 deficiency in young APP/PS1 mice exacerbates cognitive deficits and depletes the hippocampal NSC pool in later life; this can be alleviated by E2 treatment in the early period following OVX, which prevents Aβ/p75^NTR-induced NSC overproliferation and preserves telomerase activity.

ALDH2 contributes to melatonin-induced protection against APP/PS1 mutation-prompted cardiac anomalies through cGAS-STING-TBK1-mediated regulation of mitophagy

Ample clinical evidence suggests a high incidence of cardiovascular events in Alzheimer's disease (AD), although neither precise etiology nor effective treatment is available. This study was designed to evaluate cardiac function in AD patients and APP/PS1 mutant mice, along with circulating levels of melatonin, mitochondrial aldehyde dehydrogenase (ALDH2) and autophagy. AD patients and APP/PS1 mice displayed cognitive and myocardial deficits, low levels of circulating melatonin, ALDH2 activity, and autophagy, ultrastructural, geometric (cardiac atrophy and interstitial fibrosis) and functional (reduced fractional shortening and cardiomyocyte contraction) anomalies, mitochondrial injury, cytosolic mtDNA buildup, apoptosis, and suppressed autophagy and mitophagy. APP/PS1 mutation downregulated cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) levels and TBK1 phosphorylation, while promoting Aβ accumulation. Treatment with melatonin overtly ameliorated unfavorable APP/PS1-induced changes in cardiac geometry and function, apoptosis, mitochondrial integrity, cytosolic mtDNA accumulation (using both immunocytochemistry and qPCR), mitophagy, and cGAS-STING-TBK1 signaling, although these benefits were absent in APP/PS1/ALDH2-/- mice. In vitro evidence indicated that melatonin attenuated APP/PS1-induced suppression of mitophagy and cardiomyocyte function, and the effect was negated by the nonselective melatonin receptor blocker luzindole, inhibitors or RNA interference of cGAS, STING, TBK1, and autophagy. Our data collectively established a correlation among cardiac dysfunction, low levels of melatonin, ALDH2 activity, and autophagy in AD patients, with compelling support in APP/PS1 mice, in which melatonin rescued myopathic changes by promoting cGAS-STING-TBK1 signaling and mitophagy via an ALDH2-dependent mechanism.

Physical Activity Ameliorates Impaired Hippocampal Neurogenesis in the Tg4-42 Mouse Model of Alzheimer's Disease

There is growing evidence from epidemiological studies that especially midlife physical activity might exert a positive influence on the risk and progression of Alzheimer’s disease. In this study, the Tg4-42 mouse model of Alzheimer’s disease has been utilized to assess the effect of different housing conditions on structural changes in the hippocampus. Focusing on the dentate gyrus, we demonstrate that 6-month-old Tg4-42 mice have a reduced number of newborn neurons in comparison to age-matched wild-type mice. Housing these mice for 4 months with either unlimited or intermittent access to a running wheel resulted in a significant rescue of dentate gyrus neurogenesis. Although neither dentate gyrus volume nor neuron number could be modified in this Alzheimer’s disease mouse model, unrestricted access to a running wheel significantly increased dentate gyrus volume and granule cell number in wild-type mice.

Arginase Inhibition Supports Survival and Differentiation of Neuronal Precursors in Adult Alzheimer's Disease Mice

Adult neurogenesis is a complex physiological process, which plays a central role in maintaining cognitive functions, and consists of progenitor cell proliferation, newborn cell migration, and cell maturation. Adult neurogenesis is susceptible to alterations under various physiological and pathological conditions. A substantial decay of neurogenesis has been documented in Alzheimer’s disease (AD) patients and animal AD models; however, several treatment strategies can halt any further decline and even induce neurogenesis. Our previous results indicated a potential effect of arginase inhibition, with norvaline, on various aspects of neurogenesis in triple-transgenic mice. To better evaluate this effect, we chronically administered an arginase inhibitor, norvaline, to triple-transgenic and wild-type mice, and applied an advanced immunohistochemistry approach with several biomarkers and bright-field microscopy. Remarkably, we evidenced a significant reduction in the density of neuronal progenitors, which demonstrate a different phenotype in the hippocampi of triple-transgenic mice as compared to wild-type animals. However, norvaline showed no significant effect upon the progenitor cell number and constitution. We demonstrated that norvaline treatment leads to an escalation of the polysialylated neuronal cell adhesion molecule immunopositivity, which suggests an improvement in the newborn neuron survival rate. Additionally, we identified a significant increase in the hippocampal microtubule-associated protein 2 stain intensity. We also explore the molecular mechanisms underlying the effects of norvaline on adult mice neurogenesis and provide insights into their machinery.

Early Seizure Activity Accelerates Depletion of Hippocampal Neural Stem Cells and Impairs Spatial Discrimination in an Alzheimer's Disease Model

Adult hippocampal neurogenesis has been reported to be decreased, increased, or not changed in Alzheimer's disease (AD) patients and related transgenic mouse models. These disparate findings may relate to differences in disease stage, or the presence of seizures, which are associated with AD and can stimulate neurogenesis. In this study, we investigate a transgenic mouse model of AD that exhibits seizures similarly to AD patients and find that neurogenesis is increased in early stages of disease, as spontaneous seizures became evident, but is decreased below control levels as seizures recur. Treatment with the antiseizure drug levetiracetam restores neurogenesis and improves performance in a neurogenesis-associated spatial discrimination task. Our results suggest that seizures stimulate, and later accelerate the depletion of, the hippocampal neural stem cell pool. These results have implications for AD as well as any disorder accompanied by recurrent seizures, such as epilepsy.

Valproic Acid Stimulates Hippocampal Neurogenesis via Activating the Wnt/β-Catenin Signaling Pathway in the APP/PS1/Nestin-GFP Triple Transgenic Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by the deposition of amyloid-β (Aβ) peptides and neurofibrillary tangles (NFTs) and massive loss of neuronal cells in the brain. Adult hippocampus continuously generates new neurons throughout life to shape brain function and impaired neurogenesis may contribute to a series of cognitive deterioration associated with AD. Enhancing endogenous neurogenesis represents a promising strategy that may ameliorate AD-associated cognitive defects. However, neurogenesis-enhancing approaches and underlying mechanisms are still not well studied. Here, using a mouse model of AD amyloid precursor protein (APP/PS1/Nestin-GFP triple transgenic mice, 3xTgAD), we examined the effects of 4 weeks of valproic acid (VPA) treatment on hippocampal neurogenesis in 2- and 6-month-old mice. VPA treatment promoted cell proliferation and increased the density of immature neurons in the dentate gyrus (DG) of the hippocampus of 3xTgAD mice. Consistent with enhanced neurogenesis, behavioral and morphological analysis showed that VPA treatment improved the learning and memory ability of 3xTgAD mice. Mechanistically, VPA treatment increased β-catenin levels, accumulated the inactive form of glycogen synthase kinase-3β (GSK-3β), and induced the expression of NeuroD1, a Wnt target gene involved in neurogenesis, suggesting the activation of the Wnt signaling pathway in the hippocampus of 3xTgAD mice. This study indicates that VPA stimulates neurogenesis in the adult hippocampus of AD mice model through the Wnt pathway, highlighting VPA as a potential therapeutic for treating AD and related diseases.

PPARβ/δ-agonist GW0742 ameliorates dysfunction in fatty acid oxidation in PSEN1ΔE9 astrocytes

Astrocytes are the gatekeepers of neuronal energy supply. In neurodegenerative diseases, bioenergetics demand increases and becomes reliant upon fatty acid oxidation as a source of energy. Defective fatty acid oxidation and mitochondrial dysfunctions correlate with hippocampal neurodegeneration and memory deficits in Alzheimer's disease (AD), but it is unclear whether energy metabolism can be targeted to prevent or treat the disease. Here we show for the first time an impairment in fatty acid oxidation in human astrocytes derived from induced pluripotent stem cells of AD patients. The impairment was corrected by treatment with a synthetic peroxisome proliferator activated receptor delta (PPARβ/δ) agonist GW0742 which acts to regulate an array of genes governing cellular metabolism. GW0742 enhanced the expression of CPT1a, the gene encoding for a rate-limiting enzyme of fatty acid oxidation. Similarly, treatment of a mouse model of AD, the APP/PS1-mice, with GW0742 increased the expression of Cpt1a and concomitantly reversed memory deficits in a fear conditioning test. Although the GW0742-treated mice did not show altered astrocytic glial fibrillary acidic protein-immunoreactivity or reduction in amyloid beta (Aβ) load, GW0742 treatment increased hippocampal neurogenesis and enhanced neuronal differentiation of neuronal progenitor cells. Furthermore, GW0742 prevented Aβ-induced impairment of long-term potentiation in hippocampal slices. Collectively, these data suggest that PPARβ/δ-agonism alleviates AD related deficits through increasing fatty acid oxidation in astrocytes and improves cognition in a transgenic mouse model of AD.

Precision medicine and drug development in Alzheimer's disease: the importance of sexual dimorphism and patient stratification

Neurodegenerative diseases (ND) are among the leading causes of disability and mortality. Considerable sex differences exist in the occurrence of the various manifestations leading to cognitive decline. Alzheimer's disease (AD) exhibits substantial sexual dimorphisms and disproportionately affects women. Women have a higher life expectancy compared to men and, consequently, have more lifespan to develop AD. The emerging precision medicine and pharmacology concepts - taking into account the individual genetic and biological variability relevant for disease risk, prevention, detection, diagnosis, and treatment - are expected to substantially enhance our knowledge and management of AD. Stratifying the affected individuals by sex and gender is an important basic step towards personalization of scientific research, drug development, and care. We hypothesize that sex and gender differences, extending from genetic to psychosocial domains, are highly relevant for the understanding of AD pathophysiology, and for the conceptualization of basic/translational research and for clinical therapy trial design.

Trehalose Improves Cognition in the Transgenic Tg2576 Mouse Model of Alzheimer's Disease

This study assessed the therapeutic utility of the autophagy enhancing stable disaccharide trehalose in the Tg2576 transgenic mouse model of Alzheimer’s disease (AD) via an oral gavage of a 2% trehalose solution for 31 days. Furthermore, as AD is a neurodegenerative condition in which the transition metals, iron, copper, and zinc, are understood to be intricately involved in the cellular cascades leading to the defining pathologies of the disease, we sought to determine any parallel impact of trehalose treatment on metal levels. Trehalose treatment significantly improved performance in the Morris water maze, consistent with enhanced learning and memory. The improvement was not associated with significant modulation of full length amyloid-β protein precursor or other amyloid-β fragments. Trehalose had no effect on autophagy as assessed by western blot of the LC3-1 to LC3-2 protein ratio, and no alteration in biometals that might account for the improved cognition was observed. Biochemical analysis revealed a significant increase in the hippocampus of both synaptophysin, a synaptic vesicle protein and surrogate marker of synapses, and doublecortin, a reliable marker of neurogenesis. The growth factor progranulin was also significantly increased in the hippocampus and cortex with trehalose treatment. This study suggests that trehalose might invoke a suite of neuroprotective mechanisms that can contribute to improved cognitive performance in AD that are independent of more classical trehalose-mediated pathways, such as Aβ reduction and activation of autophagy. Thus, trehalose may have utility as a potential AD therapeutic, with conceivable implications for the treatment of other neurodegenerative disorders.

Early-Life Stress Does Not Aggravate Spatial Memory or the Process of Hippocampal Neurogenesis in Adult and Middle-Aged APP/PS1 Mice

Life-time experiences are thought to influence the risk to develop the neurodegenerative disorder Alzheimer’s disease (AD). In particular, early-life stress (ES) may modulate the onset and progression of AD. There is recent evidence by our group and others that AD-related neuropathological progression and the associated neuroimmune responses are modulated by ES in the classic APPswe/PS1dE9 mouse model for AD. We here extend our previous study on ES mediated modulation of neuropathology and neuroinflammation and address in the same cohort of mice whether ES accelerates and/or aggravates AD-induced cognitive decline and alterations in the process of adult hippocampal neurogenesis (AHN), a form of brain plasticity. Chronic ES was induced by limiting bedding and nesting material during the first postnatal week and is known to induce cognitive deficits by 4 months in wild type (WT) mice. The onset of cognitive decline in APP/PS1 mice generally starts around 6 months of age. We here tested mice at ages 2–4 months to study acceleration and at ages 8–10 months for aggravation of the APP/PS1 phenotype. ES-exposed WT and APP/PS1 mice were able to perform the object recognition (ORT) and location tasks (OLT) at 2 months of age. Interestingly, at 3 months, ES induced impairments in the performance of the OLT in WT, but not in APP/PS1 mice. APP/PS1 mice exhibited alterations in hippocampal cell proliferation and differentiation, but ES exposure did not further change this. At 9 months, APP/PS1 mice exhibited impaired performance in the Morris Water Maze (MWM) task, as well as reductions in markers of the AHN process, which were not further modulated by ES exposure. In addition, we observed a so far unreported hyperactivity in ES-exposed mice at 8 months of age, which hampered assessment of cognitive functions in the ORT and OLT. In conclusion, while ES has been reported to modulate AD neuropathology and neuroinflammation before, it failed to accelerate or aggravate the decline in cognition or the process of AHN in APP/PS1 mice at ages 2–4 and 8–10 months. Future studies are needed to unravel how ES might affect the vulnerability to develop AD.

Intracranial IL-17A overexpression decreases cerebral amyloid angiopathy by upregulation of ABCA1 in an animal model of Alzheimer's disease

Neuroinflammation is a pervasive feature of Alzheimer's disease (AD) and characterized by activated microglia, increased proinflammatory cytokines and/or infiltrating immune cells. T helper 17 (Th17) cells are found in AD brain parenchyma and interleukin-17A (IL-17A) is identified around deposits of aggregated amyloid β protein (Aβ). However, the role of IL-17A in AD pathogenesis remains elusive. We overexpressed IL-17A in an AD mouse model via recombinant adeno-associated virus serotype 5 (rAAV5)-mediated intracranial gene delivery. AD model mice subjected to injection of a vehicle (PBS) or rAAV5 carrying the lacZ gene served as controls. IL-17A did not exacerbate neuroinflammation in IL-17A-overexpressing mice. We found that IL-17A overexpression markedly improved glucose metabolism, decreased soluble Aβ levels in the hippocampus and cerebrospinal fluid, drastically reduced cerebral amyloid angiopathy, and modestly but significantly improved anxiety and learning deficits. Moreover, the ATP-binding cassette subfamily A member 1 (ABCA1), which can transport Aβ from the brain into the blood circulation, significantly increased in IL-17A-overexpressing mice. In vitro treatment of brain endothelial bEnd.3 cells with IL-17A induced a dose-dependent increase in protein expression of ABCA1 through ERK activation. Our study suggests that IL-17A may decrease Aβ levels in the brain by upregulating ABCA1 in blood-brain barrier endothelial cells.

Discovery of efficient stimulators for adult hippocampal neurogenesis based on scaffolds in dragon's blood

Reduction of hippocampal neurogenesis caused by aging and neurological disorders would impair neural circuits and result in memory loss. A new lead compound (N-trans-3',4'-methylenedioxystilben-4-yl acetamide 27) has been discovered to efficiently stimulate adult rats' neurogenesis. In-depth structure-activity relationship studies proved the necessity of a stilbene scaffold that is absent in highly cytotoxic analogs such as chalcones and heteroaryl rings and inactive analogs such as diphenyl acetylene and diphenyl ethane, and validated the importance of an NH in the carboxamide and a methylenedioxy substituent on the benzene ring. Immunohistochemical staining and biochemical analysis indicate, in contrast to previously reported neuroprotective chemicals, N-stilbenyl carboxamides have extra capacity for neuroproliferation-type neurogenesis, thereby providing a foundation for improving the plasticity of the adult mammalian brain.

Altered neurogenesis in mouse models of Alzheimer disease

Amyloid-β (Aβ) peptides, as well as a variety of other protein fragments, are derived from proteolytical cleavage of the amyloid precursor protein (APP) and have been demonstrated to play a key role in the pathological changes underlying Alzheimer disease (AD). In AD mouse models, altered neurogenesis has been repeatedly reported to be associated with further AD-typical pathological hallmarks such as extracellular plaque deposition, behavioral deficits or neuroinflammation. While a toxic role of Aβ in neurodegeneration and impaired neuronal progenitor proliferation is likely and well-accepted, recent findings also suggest an important influence of APP-derived proteolitical fragments like the APP intracellular domain (AICD), as well as of APP itself.

Amniotic Mesenchymal Stem Cells Decrease Aβ Deposition and Improve Memory in APP/PS1 Transgenic Mice

Transplantation of human amniotic mesenchymal stem cells (hAM-MSCs) seems to be a promising strategy for the treatment of neurodegenerative disorders, including Alzheimer's disease (AD). However, the clinical therapeutic effects of hAM-MSCs and their mechanisms of action in AD remain to be determined. Here, we used amyloid precursor protein (APP) and presenilin1 (PS1) double-transgenic mice to evaluate the effects of hAM-MSC transplantation on AD-related neuropathology and cognitive dysfunction. We found that hAM-MSC transplantation into the hippocampus dramatically reduced amyloid-β peptide (Aβ) deposition and rescued spatial learning and memory deficits in APP/PS1 mice. Interestingly, these effects were associated with increasing in Aβ-degrading factors, elevations in activated microglia, and the modulation of neuroinflammation. Furthermore, enhanced hippocampal neurogenesis in the subgranular zone (SGZ) of the dentate gyrus (DG) and enhanced synaptic plasticity following hAM-MSC treatment could be another important factor in reversing the cognitive decline in APP/PS1 mice. Instead, the mechanism underlying the improved cognition apparently involves a robust increase in hippocampal synaptic density and neurogenesis that is mediated by brain-derived neurotrophic factor (BDNF). In conclusion, our data suggest that hAM-MSCs may be a new and effective therapy for the treatment of AD.

Amplifying mitochondrial function rescues adult neurogenesis in a mouse model of Alzheimer's disease

Adult hippocampal neurogenesis is strongly impaired in Alzheimer's disease (AD). In several mouse models of AD, it was shown that adult-born neurons exhibit reduced survival and altered synaptic integration due to a severe lack of dendritic spines. In the present work, using the APPxPS1 mouse model of AD, we reveal that this reduced number of spines is concomitant of a marked deficit in their neuronal mitochondrial content. Remarkably, we show that targeting the overexpression of the pro-neural transcription factor Neurod1 into APPxPS1 adult-born neurons restores not only their dendritic spine density, but also their mitochondrial content and the proportion of spines associated with mitochondria. Using primary neurons, a bona fide model of neuronal maturation, we identified that increases of mitochondrial respiration accompany the stimulating effect of Neurod1 overexpression on dendritic growth and spine formation. Reciprocally, pharmacologically impairing mitochondria prevented Neurod1-dependent trophic effects. Thus, since overexpression of Neurod1 into new neurons of APPxPS1 mice rescues spatial memory, our present data suggest that manipulating the mitochondrial system of adult-born hippocampal neurons provides neuronal plasticity to the AD brain. These findings open new avenues for far-reaching therapeutic implications towards neurodegenerative diseases associated with cognitive impairment.

Neurogenic Traditional Chinese Medicine as a Promising Strategy for the Treatment of Alzheimer's Disease

Hippocampal neurogenesis plays a critical role in the formation of new neurons during learning and memory development. Attenuation of neurogenesis in the brain is one of the primary causes of dementia in Alzheimer’s disease (AD), and, conversely, modulating the process of hippocampal neurogenesis benefit patients with AD. Traditional Chinese medicine (TCM), particularly herbal medicine, has been in use for thousands of years in Asia and many regions of the world for the treatment of cancer, cardiovascular diseases and neurodegenerative diseases. In this review, we summarize the role of neurotrophic factors, signal transducing factors, epigenetic modulators and neurotransmitters in neurogenesis, and we also discuss the functions of several Chinese herbs and their active molecules in activating multiple pathways involved in neurogenesis. TCM herbs target pathways such as Notch, Wnt, Sonic Hedgehog and receptor tyrosine kinase pathway, leading to activation of a signaling cascade that ultimately enhances the transcription of several important genes necessary for neurogenesis. Given these pathway activating effects, the use of TCM herbs could be an effective therapeutic strategy for the treatment of AD.

Perinatal Choline Supplementation Reduces Amyloidosis and Increases Choline Acetyltransferase Expression in the Hippocampus of the APPswePS1dE9 Alzheimer's Disease Model Mice

Prevention of Alzheimer's disease (AD) is a major goal of biomedical sciences. In previous studies we showed that high intake of the essential nutrient, choline, during gestation prevented age-related memory decline in a rat model. In this study we investigated the effects of a similar treatment on AD-related phenotypes in a mouse model of AD. We crossed wild type (WT) female mice with hemizygous APPswe/PS1dE9 (APP.PS1) AD model male mice and maintained the pregnant and lactating dams on a control AIN76A diet containing 1.1 g/kg of choline or a choline-supplemented (5 g/kg) diet. After weaning all offspring consumed the control diet. As compared to APP.PS1 mice reared on the control diet, the hippocampus of the perinatally choline-supplemented APP.PS1 mice exhibited: 1) altered levels of amyloid precursor protein (APP) metabolites-specifically elevated amounts of β-C-terminal fragment (β-CTF) and reduced levels of solubilized amyloid Aβ40 and Aβ42 peptides; 2) reduced number and total area of amyloid plaques; 3) preserved levels of choline acetyltransferase protein (CHAT) and insulin-like growth factor II (IGF2) and 4) absence of astrogliosis. The data suggest that dietary supplementation of choline during fetal development and early postnatal life may constitute a preventive strategy for AD.

Early Changes in Hippocampal Neurogenesis in Transgenic Mouse Models for Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in the Western world and is characterized by a progressive loss of cognitive functions leading to dementia. One major histopathological hallmark of AD is the formation of amyloid-beta plaques, which is reproduced in numerous transgenic animal models overexpressing pathogenic forms of amyloid precursor protein (APP). In human AD and in transgenic amyloid plaque mouse models, several studies report altered rates of adult neurogenesis, i.e. the formation of new neurons from neural stem and progenitor cells, and impaired neurogenesis has also been attributed to contribute to the cognitive decline in AD. So far, changes in neurogenesis have largely been considered to be a consequence of the plaque pathology. Therefore, possible alterations in neurogenesis before plaque formation or in prodromal AD have been largely ignored. Here, we analysed adult hippocampal neurogenesis in amyloidogenic mouse models of AD at different points before and during plaque progression. We found prominent alterations of hippocampal neurogenesis before plaque formation. Survival of newly generated cells and the production of new neurons were already compromised at this stage. Moreover and surprisingly, proliferation of doublecortin (DCX) expressing neuroblasts was significantly and specifically elevated during the pre-plaque stage in the APP-PS1 model, while the Nestin-expressing stem cell population was unaffected. In summary, changes in neurogenesis are evident already before plaque deposition and might contribute to well-known early hippocampal dysfunctions in prodromal AD such as hippocampal overactivity.

Spatial training promotes short-term survival and neuron-like differentiation of newborn cells in Aβ1-42-injected rats

Neurogenesis plays a role in hippocampus-dependent learning and impaired neurogenesis may correlate with cognitive deficits in Alzheimer's disease. Spatial training influences the production and fate of newborn cells in hippocampus of normal animals, whereas the effects on neurogenesis in Alzheimer-like animal are not reported until now. Here, for the first time, we investigated the effect of Morris water maze training on proliferation, survival, apoptosis, migration, and differentiation of newborn cells in β-amyloid-treated Alzheimer-like rats. We found that spatial training could preserve a short-term survival of newborn cells generated before training, during the early phase, and the late phase of training. However, the training had no effect on the long-term survival of mature newborn cells generated at previously mentioned 3 different phases. We also demonstrated that spatial training promoted newborn cell differentiation preferentially to the neuron direction. These findings suggest a time-independent neurogenesis induced by spatial training, which may be indicative for the cognitive stimulation in Alzheimer's disease therapy.

Exercise as a pro-cognitive, pro-neurogenic and anti-inflammatory intervention in transgenic mouse models of Alzheimer's disease

It is now well established, at least in animal models, that exercise elicits potent pro-cognitive and pro-neurogenic effects. Alzheimer's disease (AD) is one of the leading causes of dementia and represents one of the greatest burdens on healthcare systems worldwide, with no effective treatment for the disease to date. Exercise presents a promising non-pharmacological option to potentially delay the onset of or slow down the progression of AD. Exercise interventions in mouse models of AD have been explored and have been found to reduce amyloid pathology and improve cognitive function. More recent studies have expanded the research question by investigating potential pro-neurogenic and anti-inflammatory effects of exercise. In this review we summarise studies that have examined exercise-mediated effects on AD pathology, cognitive function, hippocampal neurogenesis and neuroinflammation in transgenic mouse models of AD. Furthermore, we attempt to identify the optimum exercise conditions required to elicit the greatest benefits, taking into account age and pathology of the model, as well as type and duration of exercise.

A herbal medicine for Alzheimer's disease and its active constituents promote neural progenitor proliferation

Aberrant neural progenitor cell (NPC) proliferation and self-renewal have been linked to age-related neurodegeneration and neurodegenerative disorders including Alzheimer’s disease (AD). Rhizoma Acori tatarinowii is a traditional Chinese herbal medicine against cognitive decline. In this study, we found that the extract of Rhizoma Acori tatarinowii (AT) and its active constituents, asarones, promote NPC proliferation. Oral administration of AT enhanced NPC proliferation and neurogenesis in the hippocampi of adult and aged mice as well as that of transgenic AD model mice. AT and its fractions also enhanced the proliferation of NPCs cultured in vitro. Further analysis identified α-asarone and β-asarone as the two active constituents of AT in promoting neurogenesis. Our mechanistic study revealed that AT and asarones activated extracellular signal-regulated kinase (ERK) but not Akt, two critical kinase cascades for neurogenesis. Consistently, the inhibition of ERK activities effectively blocked the enhancement of NPC proliferation by AT or asarones. Our findings suggest that AT and asarones, which can be orally administrated, could serve as preventive and regenerative therapeutic agents to promote neurogenesis against age-related neurodegeneration and neurodegenerative disorders.

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.

[Fundamental study of memory impairment and non-cognitive behavioral alterations in APPswe/PS1dE9 mice]

In addition to cognitive decline, Alzheimer's disease patients also exhibit non-cognitive symptoms commonly referred to as behavioral and psychological symptoms of dementia, or BPSD. These symptoms have a serious impact on the quality of life of these patients, as well as that of their caregivers, but there are currently no effective therapies. The amyloid β-peptide (Aβ) is suspected to play a central role in the cascade leading to Alzheimer's disease, but the precise mechanisms are still incompletely known. To assess the influence of Aβ pathology on cognitive and non-cognitive behaviors, we examined locomotor activity, motor coordination, and spatial memory in male and female APPswePS1dE9 mice (Alzheimer's disease model, double transgenic mice expressing an amyloid precursor protein with Swedish mutation and a presenilin-1 with deletion of exon 9) at 5 months of age, when the mice had subtle Aβ deposits, and again at 9 months of age, when the mice had numerous Aβ deposits. Compared to wild-type mice, the male and female APPswe/PS1dE9 mice showed normal motor coordination in the rotarod test at both 5 and 9 months. In the Morris water maze test, male and female APPswe/PS1dE9 mice showed impaired spatial memory at 9 months; however, no such deficits were found at 5 months. In a locomotor activity test, male APPswe/PS1dE9 mice exhibited locomotor hyperactivity at 9 months, while females exhibited locomotor hyperactivity at both 5 and 9 months compared to the control mice. Together, these results indicate that APPswe/PS1dE9 mice developed spatial memory impairment and BPSD-like behavioral alterations resulting from Aβ accumulation.

Nrf2 regulates neurogenesis and protects neural progenitor cells against Aβ toxicity

Neural stem/progenitor cells (NPCs) proliferate and produce new neurons in neurogenic areas throughout the lifetime. While these cells represent potential therapeutic treatment of neurodegenerative diseases, regulation of neurogenesis is not completely understood. We show that deficiency of nuclear factor erythroid 2-related factor (Nrf2), a transcription factor induced in response to oxidative stress, prevents the ischemia-induced increase in newborn neurons in the subgranular zone of the dentate gyrus. Consistent with this finding, the growth of NPC neurospheres was increased by lentivirus-mediated overexpression of Nrf2 gene or by treatment with pyrrolidine dithiocarbamate (PDTC), an Nrf2 activating compound. Also, neuronal differentiation of NPCs was increased by Nrf2 overexpression or PDTC treatment but reduced by Nrf2 deficiency. To investigate the impact of Nrf2 on NPCs in Alzheimer's disease (AD), we treated NPCs with amyloid beta (Aβ), a toxic peptide associated with neurodegeneration and cognitive abnormalities in AD. We found that Aβ1-42-induced toxicity and reduction in neurosphere proliferation were prevented by Nrf2 overexpression, while Nrf2 deficiency enhanced the Aβ1-42-induced reduction of neuronal differentiation. On the other hand, Aβ1-40 had no effect on neurosphere proliferation in wt NPCs but increased the proliferation of Nrf2 overexpressing neurospheres and reduced it in Nrf2-deficient neurospheres. These results suggest that Nrf2 is essential for neuronal differentiation of NPCs, regulates injury-induced neurogenesis and provides protection against Aβ-induced NPC toxicity.

Allopregnanolone enhances the neurogenesis of midbrain dopaminergic neurons in APPswe/PSEN1 mice

An earlier study has demonstrated that exogenous allopregnanolone (APα) can reverse the reduction of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNpc) of 3-month-old male triple transgenic Alzheimer's disease mouse (3xTgAD). This paper is focused on further clarifying the origin of these new-born TH-positive neurons induced by exogenous APα treatment. We performed a deeper research in another AD mouse model, 4-month-old male APPswe/PSEN1 double transgenic AD mouse (2xTgAD) by measuring APα concentration and counting immunopositive neurons using enzyme-linked immunosorbent assay (ELISA) and unbiased stereology. It was found that endogenous APα level and the number of TH-positive neurons were reduced in the 2xTgAD mice, and these reductions were present prior to the appearance of β-amyloid (Aβ)-positive plaques. Furthermore, a single 20mg/kg of exogenous APα treatment prevented the decline of total neurons, TH-positive neurons and TH/bromodeoxyuridine (BrdU) double-positive neurons in the SNpc of 2xTgAD mice although the decreased intensity of TH-positive fibers was not rescued in the striatum. It was also noted that exogenous APα administration had an apparent increase in the doublecortin (DCX)-positive neurons and DCX/BrdU double-positive neurons of subventricular zone (SVZ), as well as in the percentage of neuronal nuclear antigen (NeuN)/BrdU double-positive neurons of the SNpc in the 2xTgAD mice. These findings indicate that a lower level of endogenous APα is implicated in the loss of midbrain dopaminergic neurons in the 2xTgAD mice, and exogenous APα-induced a significant increase in the new-born dopaminergic neurons might be derived from the proliferating and differentiation of neural stem niche of SVZ.

A neuroprotective brain-penetrating endopeptidase fusion protein ameliorates Alzheimer disease pathology and restores neurogenesis

Alzheimer disease (AD) is characterized by widespread neurodegeneration throughout the association cortex and limbic system, deposition of amyloid-β peptide (Aβ) in the neuropil and around the blood vessels, and formation of neurofibrillary tangles. The endopeptidase neprilysin has been successfully used to reduce the accumulation of Aβ following intracranial viral vector delivery or ex vivo manipulated intracranial delivery. These therapies have relied on direct injections into the brain, whereas a clinically desirable therapy would involve i.v. infusion of a recombinant enzyme. We previously characterized a recombinant neprilysin that contained a 38-amino acid brain-targeting domain. Recombinant cell lines have been generated expressing this brain-targeted enzyme (ASN12). In this report, we characterize the ASN12 recombinant protein for pharmacology in a mouse as well as efficacy in two APPtg mouse models of AD. The recombinant ASN12 transited to the brain with a t½ of 24 h and accumulated to 1.7% of injected dose at 24 h following i.v. delivery. We examined pharmacodynamics in the tg2576 APPtg mouse with the prion promoter APP695 SWE mutation and in the Line41 mThy1 APP751 mutation mouse. Treatment of either APPtg mouse resulted in reduced Aβ, increased neuronal synapses, and improved learning and memory. In addition, the Line41 APPtg mice showed increased levels of C-terminal neuropeptide Y fragments and increased neurogenesis. These results suggest that the recombinant brain-targeted neprilysin, ASN12, may be an effective treatment for AD and warrant further investigation in clinical trials.

IGF2 ameliorates amyloidosis, increases cholinergic marker expression and raises BMP9 and neurotrophin levels in the hippocampus of the APPswePS1dE9 Alzheimer's disease model mice

The development of an effective therapy for Alzheimer's disease (AD) is a major challenge to biomedical sciences. Because much of early AD pathophysiology includes hippocampal abnormalities, a viable treatment strategy might be to use trophic factors that support hippocampal integrity and function. IGF2 is an attractive candidate as it acts in the hippocampus to enhance memory consolidation, stimulate adult neurogenesis and upregulate cholinergic marker expression and acetylcholine (ACh) release. We performed a seven-day intracerebroventricular infusion of IGF2 in transgenic APPswe.PS1dE9 AD model mice that express green fluorescent protein in cholinergic neurons (APP.PS1/CHGFP) and in wild type WT/CHGFP littermates at 6 months of age representing early AD-like disease. IGF2 reduced the number of hippocampal Aβ40- and Aβ42-positive amyloid plaques in APP.PS1/CHGFP mice. Moreover, IGF2 increased hippocampal protein levels of the ACh-synthesizing enzyme, choline acetyltransferase in both WT/CHGFP and APP.PS1/CHGFP mice. The latter effect was likely mediated by increased protein expression of the cholinergic differentiating factor, BMP9, observed in IGF2-treated mice as compared to controls. IGF2 also increased the protein levels of hippocampal NGF, BDNF, NT3 and IGF1 and of doublecortin, a marker of neurogenesis. These data show that IGF2 administration is effective in reversing and preventing several pathophysiologic processes associated with AD and suggest that IGF2 may constitute a therapeutic target for AD.

Effects of specific multi-nutrient enriched diets on cerebral metabolism, cognition and neuropathology in AβPPswe-PS1dE9 mice

Recent studies have focused on the use of multi-nutrient dietary interventions in search of alternatives for the treatment and prevention of Alzheimer's disease (AD). In this study we investigated to which extent long-term consumption of two specific multi-nutrient diets can modulate AD-related etiopathogenic mechanisms and behavior in 11-12-month-old AβPPswe-PS1dE9 mice. Starting from 2 months of age, male AβPP-PS1 mice and wild-type littermates were fed either a control diet, the DHA+EPA+UMP (DEU) diet enriched with uridine monophosphate (UMP) and the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), or the Fortasyn® Connect (FC) diet enriched with the DEU diet plus phospholipids, choline, folic acid, vitamins and antioxidants. We performed behavioral testing, proton magnetic resonance spectroscopy, immunohistochemistry, biochemical analyses and quantitative real-time PCR to gain a better understanding of the potential mechanisms by which these multi-nutrient diets exert protective properties against AD. Our results show that both diets were equally effective in changing brain fatty acid and cholesterol profiles. However, the diets differentially affected AD-related pathologies and behavioral measures, suggesting that the effectiveness of specific nutrients may depend on the dietary context in which they are provided. The FC diet was more effective than the DEU diet in counteracting neurodegenerative aspects of AD and enhancing processes involved in neuronal maintenance and repair. Both diets elevated interleukin-1β mRNA levels in AβPP-PS1 and wild-type mice. The FC diet additionally restored neurogenesis in AβPP-PS1 mice, decreased hippocampal levels of unbound choline-containing compounds in wild-type and AβPP-PS1 animals, suggesting diminished membrane turnover, and decreased anxiety-related behavior in the open field behavior. In conclusion, the current data indicate that specific multi-nutrient diets can influence AD-related etiopathogenic processes. Intervention with the FC diet might be of interest for several other neurodegenerative and neurological disorders.

Impact of a multi-nutrient diet on cognition, brain metabolism, hemodynamics, and plasticity in apoE4 carrier and apoE knockout mice

Lipid metabolism and genetic background together strongly influence the development of both cardiovascular and neurodegenerative diseases like Alzheimer's disease (AD). A non-pharmacological way to prevent the genotype-induced occurrence of these pathologies is given by dietary behavior. In the present study, we tested the effects of long-term consumption of a specific multi-nutrient diet in two models for atherosclerosis and vascular risk factors in AD: the apolipoprotein ε4 (apoE4) and the apoE knockout (apoE ko) mice. This specific multi-nutrient diet was developed to support neuronal membrane synthesis and was expected to contribute to the maintenance of vascular health. At 12 months of age, both genotypes showed behavioral changes compared to control mice and we found increased neurogenesis in apoE ko mice. The specific multi-nutrient diet decreased anxiety-related behavior in the open field, influenced sterol composition in serum and brain tissue, and increased the concentration of omega-3 fatty acids in the brain. Furthermore, we found that wild-type and apoE ko mice fed with this multi-nutrient diet showed locally increased cerebral blood volume and decreased hippocampal glutamate levels. Taken together, these data suggest that a specific dietary intervention has beneficial effects on early pathological consequences of hypercholesterolemia and vascular risk factors for AD.

Aβ increases neural stem cell activity in senescence-accelerated SAMP8 mice

Neurogenesis persists in the adult brain as a form of plasticity due to the existence of neural stem cells (NSCs). Alterations in neurogenesis have been found in transgenic Alzheimer's disease (AD) mouse models, but NSC activity and neurogenesis in sporadic AD models remains to be examined. We herein describe a remarkable increase in NSC proliferation in the forebrain of SAMP8, a non-transgenic mouse strain that recapitulates the transition from healthy aging to AD. The increase in proliferation is transient, precedes AD-like symptoms such as amyloid beta 1-42 [Aβ(1-42)] increase or gliosis, and is followed by a steep decline at later stages. Interestingly, in vitro studies indicate that secreted Aβ(1-42) and PI3K signaling may account for the early boost in NSC proliferation. Our results highlight the role of soluble Aβ(1-42) peptide and PI3K in the autocrine regulation of NSCs, and further suggest that over-proliferation of NSCs before the appearance of AD pathology may underlie neurogenic failure during the age-related progression of the disease. These findings have implications for therapeutic approaches based on neurogenesis in AD.

A longitudinal study of cognition, proton MR spectroscopy and synaptic and neuronal pathology in aging wild-type and AβPPswe-PS1dE9 mice

Proton magnetic resonance spectroscopy (¹H MRS) is a valuable tool in Alzheimer’s disease research, investigating the functional integrity of the brain. The present longitudinal study set out to characterize the neurochemical profile of the hippocampus, measured by single voxel ¹H MRS at 7 Tesla, in the brains of AβPPSswe-PS1dE9 and wild-type mice at 8 and 12 months of age. Furthermore, we wanted to determine whether alterations in hippocampal metabolite levels coincided with behavioral changes, cognitive decline and neuropathological features, to gain a better understanding of the underlying neurodegenerative processes. Moreover, correlation analyses were performed in the 12-month-old AβPP-PS1 animals with the hippocampal amyloid-β deposition, TBS-T soluble Aβ levels and high-molecular weight Aβ aggregate levels to gain a better understanding of the possible involvement of Aβ in neurochemical and behavioral changes, cognitive decline and neuropathological features in AβPP-PS1 transgenic mice. Our results show that at 8 months of age AβPPswe-PS1dE9 mice display behavioral and cognitive changes compared to age-matched wild-type mice, as determined in the open field and the (reverse) Morris water maze. However, there were no variations in hippocampal metabolite levels at this age. AβPP-PS1 mice at 12 months of age display more severe behavioral and cognitive impairment, which coincided with alterations in hippocampal metabolite levels that suggest reduced neuronal integrity. Furthermore, correlation analyses suggest a possible role of Aβ in inflammatory processes, synaptic dysfunction and impaired neurogenesis.

Intrahippocampal injection of Aβ1-42 inhibits neurogenesis and down-regulates IFN-γ and NF-κB expression in hippocampus of adult mouse brain

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by accumulation of amyloid plaques and neurofibrillary tangles. Amyloid-β (Aβ) is widely recognized as a key factor in the pathogenesis of AD. Aβ1-42 a major component of amyloid plaques, has shown synaptotoxicity associated with impaired long-term potentiation and cognitive deficits. Alteration of neurogenesis in AD patients has been reported, while little is known about how Aβ1-42 affects hippocampal neurogenesis in the adult brain. In this study, we injected human Aβ1-42 peptide into hippocampal CA1 area of adult mouse brain bilaterally and evaluated histological change and neurogenesis in the hippocampus. Hematoxylin and eosin (HE) stain showed that Aβ1-42-injection resulted in an extensive neurodegeneration in the Aβ-accumulated area and CA3 in hippocampus. Immunostaining showed that intrahippocampal Aβ1-42-injection dramatically decreased the number of bromodeoxyuridine (BrdU)-positive cells in the dentate gyrus (DG) compared to the vehicle injection. Moreover, a significant decrease in the number of BrdU/double-cortin double-positive cells in Aβ1-42-injected hippocampus was observed, suggesting that Aβ1-42-injection inhibited progenitor cell proliferation and neurogenesis in subgranular zone of the DG in the adult brain. We also found that the Aβ1-42-mediated decline of neurogenesis was associated with decreased protein levels of cytokines interferon-γ (IFN-γ) and transcription factor nuclear factor-kappa B (NF-κB) in the hippocampus. These results suggest that Aβ1-42 inhibits hippocampal neurogenesis in the adult brain possibly through down-regulation of INF-γ and NF-κB signaling pathway. This study provides a new insight into Aβ1-42-mediated decrease in hippocampal neurogenesis in the adult central nervous system.

New nicotinic analogue ZY-1 enhances cognitive functions in a transgenic mice model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder marked by progressive loss of memory and cognitive function. One of the new approaches for treating AD is direct stimulation of nicotinic acetylcholine receptors (nAChRs) in the brain. α4β2-nAChR agonists have shown promising potential in preclinical cognition models of AD. The present report describes the pharmacological properties of ZY-1, a new nicotinic analogue that activates α4β2-nAChR. We describe in detail the binding profile and pharmacological effects of ZY-1 on transgenic AD mice. ZY-1 has high affinity to α4β2-nAChR. In a Morris water maze test, ZY-1 significantly decreases the escape latency and increases both the times in the platform quadrant and the times of platform crossing of transgenic mice. ZY-1 enhances cognitive functions in transgenic mice models of AD. As a novel nicotinic analogue, ZY-1 deserves further study as a potential candidate against AD.

Allopregnanolone restores hippocampal-dependent learning and memory and neural progenitor survival in aging 3xTgAD and nonTg mice

We previously demonstrated that allopregnanolone (APα) increased proliferation of neural progenitor cells and reversed neurogenic and cognitive deficits prior to Alzheimer's disease (AD) pathology (Wang, J.M., Johnston, P.B., Ball, B.G., Brinton, R.D., 2005. The neurosteroid allopregnanolone promotes proliferation of rodent and human neural progenitor cells and regulates cell-cycle gene and protein expression. J. Neurosci. 25, 4706-4718; Wang, J.M., Singh, C., Liu, L., Irwin, R.W., Chen, S., Chung, E.J., Thompson, R.F., Brinton, R.D., 2010. Allopregnanolone reverses neurogenic and cognitive deficits in mouse model of Alzheimer's disease. Proc. Natl. Acad. Sci. U. S. A. 107, 6498-6503). Herein, we determined efficacy of APα to restore neural progenitor cell survival and associative learning and memory subsequent to AD pathology in male 3xTgAD mice and their nontransgenic (nonTg) counterparts. APα significantly increased survival of bromodeoxyuridine positive (BrdU+) cells and hippocampal-dependent associative learning and memory in 3xTgAD mice in the presence of intraneuronal amyloid beta (Aβ) whereas APα was ineffective subsequent to development of extraneuronal Aβ plaques. Restoration of hippocampal-dependent associative learning was maximal by the first day and sustained throughout behavioral training. Learning and memory function in APα-treated 3xTgAD mice was 100% greater than vehicle-treated and comparable to maximal normal nonTg performance. In aged 15-month-old nonTg mice, APα significantly increased survival of bromodeoxyuridine-positive cells and hippocampal-dependent associative learning and memory. Results provide preclinical evidence that APα promoted survival of newly generated cells and restored cognitive performance in the preplaque phase of AD pathology and in late-stage normal aging.