Cholinergic neuropathology in a mouse model of Alzheimer's disease

Transgenic mice overexpressing mutant human amyloid precursor protein (PDAPP mice) develop several Alzheimer's disease (AD)-like lesions including an age-related accumulation of amyloid-beta (Abeta)-containing neuritic plaques. Although aged, heterozygous PDAPP mice also exhibit synaptic and glial cell changes characteristic of AD pathology, no evidence of widespread neuronal loss has been observed. The present study sought to determine whether homozygous PDAPP mice, which express very high levels of Abeta peptide, exhibit AD-like cholinergic degenerative changes, and whether the changes parallel the deposition of Abeta plaques. Mice were examined at 2 and 4 months and at 1 and 2 years of age. There was an age-related increase in the density of Abeta plaques in the cortex and hippocampus of the PDAPP animals; at 4 months of age there were very few plaques, and at 2 years there was a very high density of plaques. There was an age-related reduction in the density of cholinergic nerve terminals in the cerebral cortex; at 2 months there was a normal density of nerve terminals, but as early as age 4 months there was an approximately 50% reduction. However, at age 2 years there was no difference in the number or size of basal forebrain cholinergic somata compared with 2-month-old PDAPP mice. These data indicated that the homozygous PDAPP mouse exhibits cholinergic nerve terminal degenerative pathology and that the cortical neurodegenerative changes occur before the deposition of Abeta-containing neuritic plaques.     

Memory function in a mouse genetic model of Alzheimer's disease

The E4 allele of the apolipoprotein E (ApoE) gene has been identified as a major risk factor for the development of late onset Alzheimer's disease (AD). However, the mechanisms by which this gene affects AD are not fully understood. Studies of ApoE knock-out (ApoE KO) mice have revealed an exacerbation of two major pathologies that are diagnostic of AD: neurofibrillary tangles and senile plaques. However, evidence as to whether these mice have cognitive deficits is not yet conclusive. This ambiguity may arise partly from confounds associated with reliance on limited memory models, primarily, the Morris water maze task. An 8-arm radial maze task was therefore used to measure spatial memory in the ApoE KO mice, compared to controls over time. Furthermore, the effectiveness of a combination antioxidant therapy (CAT), designed to slow down the progression of AD based on concepts of oxidative stress and inflammatory processes underlying the pathology, was tested on memory ability. A significant strain difference was observed with the ApoE KO mice performing better than controls in terms of reference memory and corrects entries. No significant strain difference was observed for performance in terms of working memory errors. No significant effect of the CAT supplementation was observed.     

Brainstem Alzheimer's-like pathology in the triple transgenic mouse model of Alzheimer's disease

The triple transgenic mouse (3xTgAD), harboring human APP_Swe, PS1_M146V and Tau_P301L genes, develops age-dependent forebrain intraneuronal Aβ and tau as well as extraneuronal plaques. We evaluated brainstem AD-like pathology using 6E10, AT8, and Alz50 antibodies and unbiased stereology in young and old 3xTgAD mice. Intraneuronal Aβ occurred in the tectum, periaqueductal gray, substantia nigra, red nucleus, tegmentum and mesencephalic V nucleus at all ages. Aβ-positive neuron numbers significantly decreased in the superior colliculus and substantia nigra while AT8-positive superior colliculus, red nucleus, principal sensory V, vestibular nuclei, and tegmental neurons significantly increased between 2 and 12 months. Alz50-positive neuron numbers increased only in the inferior colliculus between these ages. Dual labeling revealed a few Aβ- and tau-positive neurons. Plaques occurred only in the pons of female 3xTgAD mice starting at 9 months. 3xTgAD mice provide a platform to define in vivo mechanisms of Aβ and tau brainstem pathology.     

Decreased adult hippocampal neurogenesis in the PDAPP mouse model of Alzheimer's disease

Abnormal subgranular zone (SGZ) neurogenesis is proposed to contribute to Alzheimer's disease (AD)-related decreases in hippocampal function. Our goal was to examine hippocampal neurogenesis in the PDAPP mouse, a model of AD with age-dependent accumulation of amyloid-beta(42) (Abeta(42))-containing plaques that is well studied with regard to AD therapies. A secondary goal was to determine whether altered neurogenesis in the PDAPP mouse is associated with abnormal maturation or number of mature cells. A tertiary goal was to provide insight into why hippocampal neurogenesis appears to be increased in AD post-mortem tissue and decreased in most AD mouse models. We report an age-dependent decrease in SGZ proliferation in homozygous PDAPP mice. At 1 year of age, PDAPP mice also had new dentate gyrus granule neurons with abnormal maturation and fewer dying cells relative to control mice. In contrast to decreased SGZ cell birth, PDAPP mice had increased birth of immature neurons in the outer portion of the granule cell layer (oGCL), providing insight into why some studies link AD with increased neurogenesis. However, these ectopic oGCL cells were still rare compared with SGZ proliferating cells, emphasizing that the primary characteristic of PDAPP mice is decreased neurogenesis. The decrease in SGZ neurogenesis was not associated with an age-dependent loss of dentate granule neurons. The altered neurogenesis in the PDAPP mouse may contribute to the age-related cognitive deficits reported in this model of AD and may be a useful adjunct target for assessing the impact of AD therapies.     

Loss of presenilin function causes Alzheimer's disease-like neurodegeneration in the mouse

Accumulating evidence has indicated that gain-of-function in beta-amyloid production may be not the necessary mechanism for mutant presenilin-1 (PS1) or PS2 to cause familial Alzheimer's disease (AD). In the present article, we show that conditional knockout of PS1 from the adult stage in the forebrain of mice with the PS2 null mutation triggers robust AD-like neurodegeneration including brain shrinkage, cortical and hippocampal atrophy,ventricular enlargement, severe neuronal loss, gliosis, tau hyperphosphorylation, neurofillament tangle-like structures, and intracellular filaments. Learning and memory functions in these mice are almost completely lost. Notably, there is no beta-amyloid deposition, indicating that presenilin dysfunction can directly cause neurodegeneration without the involvement of beta-amyloid. Furthermore, neurodegeneration occurs in a progressive manner following aging, suggesting that an accumulating effect of presenilin dysfunction over time might be a pathogenic mechanism for the involvement of mutant PS1/PS2 in causing AD. These results validate a mouse model characterized by the presence of many features of AD pathology. Furthermore, the demonstration of AD-like neurodegeneration in the absence of beta-amyloid deposition challenges the long-standing beta-amyloid cascade hypothesis and encourages an open debate on the role of beta-amyloid in causing AD. Most important, our results strongly suggest that to develop gamma-secretase inhibitors for the pharmacological treatment of AD may be not a reasonable strategy because antagonism of presenilin function may worsen neurodegeneration.     

Loss of motor function in preclinical Alzheimer's disease

Accumulating evidence suggests that Alzheimer's disease (AD) has a long preclinical phase, during which time its characteristic pathology accumulates and patient function declines, but symptoms are insufficient to warrant a clinical diagnosis of dementia. There have been increasing reports of noncognitive symptoms, including loss of motor function, reported to be associated with incident AD. To understand the link between motor function and preclinical AD, this article examines: our understanding of motor function and its clinical assessment in cohort studies; the relationship of motor function and loss of cognition in older persons; risk factors for cognitive and motor decline; and the relation of post-mortem indices of AD and motor function prior to death. Together, these data suggest that age-related cognitive and motor decline may share a common causation. Furthermore, individuals with a clinical diagnosis of AD may represent the 'tip of the iceberg', since AD pathology may also account for a substantial proportion of cognitive and motor dysfunction currently considered 'normal aging' in older persons without dementia. Thus, AD may have a much larger impact on the health and wellbeing of our aging population.     

Abundant type 10 17 beta-hydroxysteroid dehydrogenase in the hippocampus of mouse Alzheimer's disease model

A full-length cDNA of mouse type 10 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD10) was cloned from brain, representing the accurate nucleotide sequence information that rendered possible an accurate deduction of the amino acid sequence of the wild-type enzyme. A comparison of sequences and three-dimensional models of this enzyme revealed that structures previously reported by other groups carry either a truncated or mutated amino-terminal sequence. Fusion of the first 11 residues of the wild-type enzyme to the green fluorescent protein directed the reporter protein into mitochondria. Thus, the N-terminus was identified as a mitochondrial targeting signal that accounts for the intracellular localization of the mouse enzyme. This enzyme is normally associated with mitochondria, not with the endoplasmic reticulum as suggested by its trivial name 'endoplasmic reticulum-associated amyloid-beta biding protein (ERAB)'. After its C-terminal region was used to raise rabbit anti-17 betaHSD10 antibodies, immunogold electron microscopy showed that an abundance of this enzyme could be found in hippocampal synaptic mitochondria of betaAPP transgenic mice, but not in normal controls. High levels of this enzyme may disrupt steroid hormone homeostasis in synapses and contribute to synapse loss in the hippocampus of the mouse Alzheimer's disease model.     

Loss of the cortisol response to naltrexone in Alzheimer's disease

The administration of a single dose of the opiate antagonist naltrexone (NT) was accompanied by significant elevations in plasma cortisol in normal elderly subjects; in contrast, the cortisol response to NT was absent in individuals of comparable age with Alzheimer's disease (AD). The differential effect of AD on the cortisol response was not accompanied by a significant group difference in plasma prolactin in response to NT administration. Furthermore, this differential cortisol response to NT was not associated with any evident differences in age, sex ratio, plasma levels of naltrexone or its major metabolite beta-naltrexol, or with differences in measures of nonspecific stress, such as plasma free MHPG, pulse, or blood pressure, between the two groups. The absence of the well-characterized cortisol response to NT in AD, together with other reports of abnormal responses to other pharmacological challenges, suggests that neuroendocrine abnormalities might be an important concomitant and possibly a central contributor to the pathophysiology of Alzheimer's disease.     

胆碱能神经干细胞在阿尔茨海默病小鼠的移植研究

目的 观察胆碱能神经干细胞移植对阿尔茨海默病(AD)小鼠的治疗效果.方法 C57BL/6小鼠基底巨细胞核注射Ibotenic酸制成AD模型.4周后于额叶和顶叶皮质移植小鼠胚胎干细胞源性胆碱能神经干细胞.存移植术后12周,应用HE染色和且日碱乙酰转移酶-绿色荧光蛋白免疫双标染色观察神经干细胞存活和分化情况,以8方向迷宫试验评价小鼠近事记忆的改善程度.结果 胆碱能神经十细胞移植至AD小鼠顶叶和额叶皮质后主要分化为成熟胆碱能神经元,并移行和整合至移植区周围皮质,该区皮质β-淀粉样蛋白表达明显减少,且小鼠的近事记忆明显改善.结论 胆碱能神经十细胞移植可部分重建AD小鼠的胆碱能支配,改善近事记忆损害.     

A possible link between astrocyte activation and tau nitration in Alzheimer's disease

Alzheimer's disease (AD) pathology has been characterized, in part, by the self-assembly of the tau molecule into neurofibrillary tangles (NFT). While different post-translational modifications have been identified that accelerate tau aggregation, nitration at tyrosine residues prevents or slows tau filament formation in vitro. Of the five tyrosine residues within the molecule, nitration at the first tyrosine residue (Tyr 18) results in a profound inhibition of filament self-assembly. To determine whether nitration at Tyr 18 occurs in AD pathology, monoclonal antibodies were raised against a synthetic tau peptide nitrated at Tyr 18. A clone, termed Tau-nY18, reacts specifically with tau proteins nitrated at Tyr 18 and fails to cross-react with other nitrated tyrosine residues spanning the length of the molecule or with other proteins known to be nitrated in neurodegenerative diseases. In situ, Tau-nY18 sparsely labels the neuronal pathological hallmarks of the disease, including NFT and dystrophic neurites. Surprisingly however, Tau-nY18 robustly labels nitrated tau within activated, GFAP positive astrocytes intimately associated with amyloid plaques. Furthermore, this antibody detects nitrated tau in soluble preparations from both severe AD brains (Braak stage V, VI) and age-matched controls. Collectively, these findings suggest that nitration at Tyr 18 may be linked to astrocyte activation, an early event associated with amyloid plaque formation.     

Age-dependent and tissue-related glutathione redox status in a mouse model of Alzheimer's disease

Glutathione plays an essential role in the intracellular antioxidant defense against oxidant radicals, especially the ?OH radical. To understand the early and progressive cellular changes in the development of Alzheimer's disease (AD), we investigated reduced glutathione/oxidized glutathione (GSH/GSSG) status in a double mutated AD transgenic mouse model (B6.Cg-Tg), which carries Swedish amyloid-β protein precursor mutation (AβPPswe) and exon 9 deletion of the PSEN1 gene. In this study, we quantified and compared both GSH/GSSG and mixed-disulfide (Pr-SSG) levels in blood samples and three anatomic positions in brain (cerebrum, cerebellum, and hippocampus) at 3 age stages (1, 5, and 11 months) of AD transgenic (Tg)/wild type mice. The present study was designed to characterize and provide insight into the glutathione redox state of both brain tissues and blood samples at different disease stages of this Tg model. The level of Pr-SSG increased in all AD brain tissues and blood compared with controls regardless of age. The GSH/GSSG ratio in AD-Tg brain tissue started at a higher value at 1 month, fell at the transitional period of 5 months, right before the onset of amyloid plaques, followed by an increase in GSSG and associated decrease of GSH/GSSG at 11 months. These results suggest that formation of Pr-SSG may be an early event, preceding amyloid plaque appearance, and the data further implies that tissue thiol redox is tightly regulated. Notably, the high basal levels of mixed-disulfides in hippocampus suggest a potential for increased oxidative damage under oxidizing conditions and increased GSSG in this vulnerable region.     

The PDAPP mouse model of Alzheimer's disease: locus coeruleus neuronal shrinkage

Alzheimer's disease is characterized by neuronal degeneration in the cerebral cortex and hippocampus and subcortical neuronal degeneration in such nuclei as the locus coeruleus (LC). Transgenic mice overexpressing mutant human amyloid precursor protein V717F, PDAPP mice, develop several Alzheimer's disease-like lesions. The present study sought to determine whether there is also loss of LC noradrenergic neurons or evidence of degenerative changes in these animals. PDAPP hemizygous and wild-type littermate control mice were examined at 23 months of age, at a time when there are numerous amyloid-beta (Abeta) plaques in the neocortex and hippocampus. Tissue sections were stained immunohistochemically with an antibody against tyrosine hydroxylase (TH) to identify LC neurons. Computer imaging procedures were used to count the TH-immunoreactive somata in sections through the rostral-caudal extent of the nucleus. There was no loss of LC neurons in the hemizygous mice. In a second experiment, homozygous PDAPP and wild-type mice were examined, at 2 months and 24 months of age. Again there was no age-related loss of neurons in the homozygous animals. In the portion of the LC where neurons reside that project to the cortex and hippocampus, however, the neurons were decreased in size selectively in the 24-month-old transgenic animals. These data indicate that overt LC cell loss does not occur following abundant overexpression of Abeta peptide. However, the selective size reduction of the LC neuronal population projecting to cortical and hippocampal regions containing Abeta-related neuropathology implies that these cells may be subjected to a retrograde-mediated stress.     

Loss of cortical GABA uptake sites in Alzheimer's disease

Summary [³H]Nipecotic acid bound to membranes of human brain in a saturable, reversible manner which was totally dependent on the presence of sodium ions. The potencies of compounds in inhibiting the specific binding of [³H] nipecotic acid were closely correlated with their potencies in inhibiting the neuronal uptake of [³H]GABA. Compounds selective for GABA receptors were inactive. [³H]Nipecotic acid appears to label neuronal high affinity GABA uptake sites. The binding of [³H]nipecotic acid was substantially reduced in the temporal cortex of brains from subjects with Alzheimer-type dementia, but not in other brain regions. It is concluded that some loss of GABA terminals occurs in this disease.     

Differential cell proliferation in the cortex of the APPswePS1dE9 Alzheimer's disease mouse model

Plaque deposition in Alzheimer's disease (AD) is known to decrease proliferation in neurogenic niches in AD mouse models, but the effects on cell proliferation and differentiation in other brain areas have not been studied in detail. We analyzed cell proliferation in the cortex of wild type (WT) and APPswePS1dE9 transgenic (AD) mice at different ages. Mice were studied shortly after the last BrdU injection (BrdU[ST]). In AD mice, the number of proliferating cells increased fourfold, coinciding with plaque appearance and its associated reactive gliosis and activation of microglia. An increase in the number of BrdU[ST]-cells expressing markers for activated microglia is underlying the enhanced proliferation. Cortical reactive astrocytes did not become proliferative since BrdU[ST]-cells were negative for different astrocyte-specific markers. The number of Olig2-positive oligodendrocyte precursor cells was unchanged. Four weeks after the last BrdU application, the number of BrdU[LT]-cells with an activated microglia signature was still enhanced in AD mice. None of the newborn cells had differentiated into oligodendrocytes, astrocytes, or neurons. On the basis of these observations, we conclude that amyloid plaque deposition increases proliferation of microglia around plaques but does not affect the proliferation of cortical oligodendrocyte precursor cells. No evidence was found for damage-induced proliferation of reactive astrocytes or for a redirected neurogenesis from the subventricular zone. The proliferation of microglia contributes to the rapid accumulation of microglia around plaques and may play a role in limitating plaque expansion.     

Permeability of proteins at the blood-brain barrier in the normal adult mouse and double transgenic mouse model of Alzheimer's disease

The permeability of albumin, insulin, and human A beta 1--40 at the blood-brain barrier (BBB) was determined in the normal adult mouse (B6/SJL) and in the double transgenic Alzheimer mouse (APP, PS1) by using an I.V. bolus injection technique to quantify the permeability coefficient-surface area (PS) product for each protein after correction for the residual plasma volume (V(p)) occupied by the protein in the blood vessels of different brain regions using a second aliquot of the same protein radiolabeled with a different isotope of iodine ((125)I vs (131)I) as a vascular space marker. This technology for quantifying BBB permeability of proteins was adapted from the rat to the mouse and involved catheterizing the femoral artery and vein of the mouse instead of the brachial artery and vein as for the rat. Because of the smaller blood volume in the mouse, serial sampling (20 microl) of blood from the femoral artery of the mouse was performed and directly TCA precipitated to generate a whole blood washout curve for the intact protein. When similar blood sampling techniques were used in the rat, the PS values for albumin and insulin at the BBB were similar in these two species. In the double transgenic mouse, the V(p) values for albumin were significantly increased 1.4- to 1.6-fold in five of six brain regions compared to the normal adult mouse, which indicated increased adherence of albumin to vessel walls. As a result, the PS values were significantly decreased, from 1.4- to 3.2-fold, which likely reflected decreased transport of albumin by passive diffusion. In contrast, insulin, which is taken up into the brain by a receptor-mediated transport mechanism at the BBB, showed no significant difference in the V(p) values but a significant increase in the PS values in four of six brain regions. This suggests a compensatory mechanism in the Alzheimer's transgenic brain whereby there is an increased permeability to insulin at the BBB. Surprisingly, there was no significant difference in the V(p) or PS values for human A beta 1--40 at the BBB in the double transgenic Alzheimer mouse at 24, 32, or 52 weeks of age, when there is both significant A beta levels in the plasma and amyloid burden in the brains of these animals. These data suggest that there is not an alteration in permeability to human A beta 1--40 at the BBB with increasing amyloid burden in the double transgenic Alzheimer mouse. Although these observations suggest structural alterations at the BBB, they do not support the concept of extensive BBB damage with substantial increases in BBB permeability in Alzheimer's disease.     

Age-related impairments in operant DMTP performance in the PS2APP mouse, a transgenic mouse model of Alzheimer's disease

One of the earliest signs of Alzheimer's disease (AD) is loss of memory for recent events. This deficit in short term memory has been characterised in mild/moderate AD patients as a delay-dependent deficit in a delayed matching to sample (DMTS) task. PS2APP mice co-expressing hPS2mut and hAPPswe exhibit a spatial-temporal elevation in brain amyloid deposition and inflammation associated with temporal cognitive decline. The aim of the current study was to train PS2APP mice (C57BL/6JxDBA/2 mixed background) and appropriate control mice (B6D2F1 background) in a rodent delayed response task, the delayed matching to position (DMTP) task, prior to the onset of plaque formation and subsequently at 2-4 monthly intervals to investigate the effect of aging and increasing plaque load on DMTP performance. At 5 months of age (baseline) DMTP performance was equivalent with both PS2APP and control mice demonstrating a working memory curve across increasing delay intervals of 1-24s. A comparison of PS2APP and control mice across ages revealed a selective age-related, delay-dependent, impairment on choice accuracy in PS2APP mice, consistent with the cognitive decline and temporal amyloidosis previously described for this mouse model. These data are also relevant for other conditional transgenic mouse models which allow time-sensitive induction or inhibition of gene expression such that mice can be trained to perform the task prior to activation or inactivation of the gene and tested thereafter.     

Lactoferrin modification of berberine nanoliposomes enhances the neuroprotective effects in a mouse model of Alzheimer's disease

Previous studies have shown that berberine has neuroprotective effects against Alzheimer’s disease, including antagonizing tau phosphorylation, and inhibiting acetylcholinesterase activity and neural cell apoptosis. However, its low bioavailability and adverse reactions with conventional administration limit its clinical application. In this study, we prepared berberine nanoliposomes using liposomes characterized by low toxicity, high entrapment efficiency, and biodegradability, and modified the...     

Gastrodin alleviates memory deficits and reduces neuropathology in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive, neurodegenerative disease, characterized by excessive accumulation of amyloid‐beta (Aβ) and activation of microglia cells and astrocytes. In this research, we evaluated whether gastrodin, an active component isolated from the rhizome of Gastrodia elata, has neuroprotective effects in a mouse model of AD, Tg2576 mice. Treatment of gastrodin (60 mg/kg for 15 days) significantly improved memory impairments in the Morris water maze test and probe test. Moreover, immunohistochemical and ELISA results indicated that gastrodin significantly attenuated Aβ deposition and glial activation in brains of these transgenic mice. These findings suggested that gastrodin exerted neuroprotective activity via anti‐inflammatory and anti‐amyloidogenic effects and that gastrodin may be a potential option for AD therapy.     

Effect of normobaric hyperoxia on behavioral deficits and neuropathology in Alzheimer's disease mouse model

Amyloid plaques in the brains are the pathological hallmark of Alzheimer's disease (AD). Amyloid-β (Aβ), the central component of amyloid plaques, is generated from amyloid-β protein precursor (AβPP), following β- and γ-secretase cleavage. The molecular mechanism underlying the pathogenesis of AD is still unknown and there has been no effective treatment for AD. Clinical data showed that brain cerebral perfusion of most AD patients was reduced before memory and cognitive impairment incurred. Hypoxia is the direct consequence of hypoperfusion. Improving oxygen supply in the brain might exert potential effective influence on AD pathology. Normobaric hyperoxia (NBO), in addition to serving as a tool for enhancement of oxygen delivery, was protective in recent experimental and clinical pilot studies as well. In the present study, we evaluated the potential neuroprotective effects of NBO on behavioral deficits and neuropathology in AD. Morris water maze tests showed that NBO treatment notably improved the spatial learning and memory deficits in AβPP/PS1 transgenic mice. Immunohistochemical and thioflavin S staining showed that NBO treatment significantly decreased Aβ deposition and neuritic plaques formation in the cortex and hippocampus of AβPP/PS1 transgenic mice. Immunoblotting and ELISA assay revealed that NBO treatment reduced Aβ production by inhibiting γ-secretase cleavage of AβPP. Our study suggests that NBO may have a potential therapeutic effect at the early stage of AD.     

A cholesterol-lowering drug reduces beta-amyloid pathology in a transgenic mouse model of Alzheimer's disease

Clinical, epidemiological, and laboratory studies suggest that cholesterol may play a role in the pathogenesis of Alzheimer's disease (AD). Transgenic mice exhibiting an Alzheimer's beta-amyloid phenotype were treated with the cholesterol-lowering drug BM15.766 and tested for modulation of beta-amyloid levels. BM15.766 treatment reduced plasma cholesterol, brain Abeta peptides, and beta-amyloid load by greater than twofold. A strong, positive correlation between the amount of plasma cholesterol and Abeta was observed. Furthermore, drug treatment reduced the amyloidogenic processing of the amyloid precursor protein, suggesting alterations in processing in response to cholesterol modulation. This study demonstrates that hypocholesterolemia is associated with reduced Abeta accumulation suggesting that lowering cholesterol by pharmacological means may be an effective approach for reducing the risk of developing AD.