Regional variations in the transport of interleukin-1alpha across the blood-brain barrier in ICR and aging SAMP8 mice

OBJECTIVES: The blood-brain barrier (BBB) transports blood-borne interleukin-1alpha (IL-1) into the brain by a saturable process. Here, we determined whether all regions of the brain could transport IL-1 and whether transport differed between ICR and SAMP8 mice, a strain which overexpresses amyloid beta protein (Abeta) with aging. METHODS: We used multiple-time regression analysis to measure the unidirectional influx rate (transport rate) of radioactively labeled IL-1 for 10 brain regions in young (2 months old) ICR mice and in young and aged (17 months old) SAMP8 mice. We also used radioactively labeled sucrose and albumin to determine whether the BBB was disrupted in aged SAMP8 mice. RESULTS: In young ICR mice, eight of the 10 brain regions transported IL-1, with the pons-medulla having the fastest transport rate (0.584 +/- 0.163 microl/g x min), but no statistically significant differences occurred among regions. In SAMP8 mice, only four regions transported IL-1. In young SAMP8 mice, the pons-medulla transported IL-1 faster than any other region (0.642 +/- 0.197 microl/g x min), a rate that was significantly different (p < 0.01) from each of the other regions. Aged SAMP8 mice had a similar regional transport pattern to young SAMP8 mice, but there were no statistically significant differences among the four transporting regions. Sucrose and albumin spaces were not increased in aged SAMP8 mice, demonstrating an intact BBB. CONCLUSIONS: The smaller number of regions transporting IL-1 in SAMP8 mice as compared to ICR mice demonstrates a genetic influence on transport which could alter the ability of blood-borne IL-1 to directly affect brain functions. No evidence of BBB disruption was found in the aged SAMP8 mice from this colony.     

Antisense directed at the Abeta region of APP decreases brain oxidative markers in aged senescence accelerated mice

Amyloid beta-peptide (Abeta) is known to induce free radical-mediated oxidative stress in the brain. Free radical-mediated damage to the neuronal membrane components has been implicated in the etiology of Alzheimer's disease (AD). Abeta is produced by proteolytic processing of the amyloid precursor protein (APP). The senescence accelerated mouse prone 8 (SAMP8) strain was developed by phenotypic selection from a common genetic pool. The SAMP8 strain exhibits age-related deterioration in memory and learning as well as Abeta accumulation, and it is considered an effective model for studying brain aging in accelerated senescence. Previous research has shown that a phosphorothiolated antisense oligonucleotide directed against the Abeta region of APP decreases the expression of APP and reverses deficits in learning and memory in aged SAMP8 mice. Consistent with other reports, our previous study showed that 12-month-old SAMP8 mice have increased levels of oxidative stress markers in the brain compared with that in brains from 4-month-old SAMP8 mice. In the current study, 12-month-old SAMP8 mice were treated with antisense oligonucleotide directed against the Abeta region of APP, and the oxidative markers in brain were decreased significantly. Therefore, we conclude that Abeta may contribute to the oxidative stress found in aged SAMP8 mice that have learning and memory impairments. These results are discussed in reference to AD.     

Impairments in brain-to-blood transport of amyloid-β and reabsorption of cerebrospinal fluid in an animal model of Alzheimer's disease are reversed by antisense directed against amyloid-β protein precursor

The blood-brain barrier (BBB) influences brain levels of amyloid-β (Aβ) by transporting Aβ out of the brain (efflux) and by the reabsorption of cerebrospinal fluid (CSF) into the blood stream (bulk flow). In Alzheimer's disease (AD) and normal aging, unknown factors impair Aβ efflux and bulk flow in aging and in AD. These impairments have been proposed as mechanisms by which the Aβ burden in brain can increase. Impairment in Aβ efflux occurs in animal models of AD, including the aged SAMP8 mouse. Here, we show that CSF reabsorption is also reduced by about 50% in SAMP8 mice (p < 0.05). We then determined whether an antisense directed at the Aβ region of the amyloid-β protein precursor (AβPP) and previously shown to decrease brain levels of AβPP and to reverse the cognitive impairments of the SAMP8 mouse was able to reverse these impairments. We found that the antisense restored both the CSF reabsorption, more than doubling the rate of efflux, and the saturable efflux of Aβ. These findings suggest that AβPP/Aβ itself contributes to the impairments in bulk flow and saturable efflux of Aβ and that reduction of AβPP/Aβ levels can restore normal function of the BBB.     

Proteomic identification of less oxidized brain proteins in aged senescence-accelerated mice following administration of antisense oligonucleotide directed at the Abeta region of amyloid precursor protein

Amyloid beta-peptide (Abeta) is the major constituent of senile plaques, a pathological hallmark of Alzheimer's disease (AD) brain. It is generally accepted that Abeta plays a central role in the pathophysiology of AD. Abeta is released from cells under entirely normal cellular conditions during the internalization and endosomal processing of amyloid precursor protein (APP). However, accumulation of Abeta can induce neurotoxicity. Our previous reports showed that decreasing the production of Abeta by giving an intracerebroventricular injection of a 42-mer phosphorothiolated antisense oligonucleotide (AO) directed at the Abeta region of the APP gene reduces lipid peroxidation and protein oxidation and improves cognitive deficits in aged senescence-accelerated mice prone 8 (SAMP8) mice. In order to investigate how Abeta level reduction improves learning and memory performance of SAMP8 mice through reduction of oxidative stress in brains, we used proteomics to identify the proteins that are less oxidized in 12-month-old SAMP8 mice brains treated with AO against the Abeta region of APP (12 mA) compared to that of the age-control SAMP8 mice. We found that the specific protein carbonyl levels of aldoase 3 (Aldo3), coronin 1a (Coro1a) and peroxiredoxin 2 (Prdx2) are significantly decreased in the brains of 12 mA SAMP8 mice compared to the age-controlled SAMP8 treated with random AO (12 mR). We also found that the expression level of alpha-ATP synthase (Atp5a1) was significantly decreased, whereas the expression of profilin 2 (Pro-2) was significantly increased in brains from 12 mA SAMP8 mice. Our results suggest that decreasing Abeta levels in aged brain in aged accelerated mice may contribute to the mechanism of restoring the learning and memory improvement in aged SAMP8 mice and may provide insight into the role of Abeta in the memory and cognitive deficits in AD.     

Age-related alteration in cerebral blood flow and energy failure is correlated with cognitive impairment in the senescence-accelerated prone mouse strain 8 (SAMP8)

Cerebrovascular dysfunction is an early pathogenic event in Alzheimer’s disease (AD) and plays a key role in the disease process. Cerebral hypoperfusion, brain glucose hypometabolism and disrupted blood–brain barrier (BBB) integrity contributed to the onset and progression of AD. However, the relationships between the age-related cognitive impairment and cerebral blood flow (CBF), energy metabolism and BBB have not been clearly explained. In this study, we investigated the cognitive function, CBF, BBB damage and expression level of glucose transporter (GLUT) 1 and 3 of senescence-accelerated mouse prone 8 (SAMP8), and the correlations between each of them were analyzed. When compared with SAMR1 (senescence-accelerated mouse resistant 1), the cognitive abilities of SAMP8 were damaged apparently even at 4 months of age, showing up a slower and more capricious acquisition in Morris water maze tasks. In both SAMP8 and SAMR1, reduced CBF and increased BBB leakage were observed with increasing age, but an earlier and more severe impairment was detected in SAMP8. In addition, alterations of GLUT1 and GLUT3 protein expression in cortex and hippocampus were more prominent in SAMP8. Correlation analysis demonstrated that the increased escape latency was correlated negatively with CBF and expression of glucose transporters; and positively with BBB permeability in the hippocampus. These results suggested that CBF, BBB integrity, the expression of GLUT1 and GLUT3 were significantly affected by age and strain, which were also closely associated with cognitive ability. The alteration in CBF and energy failure induced by aging and vascular insults resulted in cognitive decline in SAMP8.     

Blood-brain barrier permeability correlates with medial temporal lobe atrophy but not with amyloid-beta protein transport across the blood-brain barrier in Alzheimer's disease

BACKGROUND/AIMS: Alterations in the blood-brain barrier (BBB) may play an important role in the pathogenesis and treatment of Alzheimer's disease (AD). We investigated BBB disturbance and its influence on the equilibrium of amyloid-beta protein (Abeta) between plasma and cerebrospinal fluid (CSF) in AD patients. METHODS: We analyzed albumin ratio as a marker of the BBB permeability and correlated it with the severity of dementia, brain atrophy on MRI, apolipoprotein E isoform, CSF levels of total tau, CSF and plasma levels of Abeta 1-40 (Abeta40) and 1-42 (Abeta42), and CSF/plasma ratios of Abeta40 and Abeta42 in 42 AD patients. RESULTS: The albumin ratio was positively correlated with the severity of medial temporal lobe atrophy but not with the other parameters including CSF/plasma ratios of Abeta40 or Abeta42. CONCLUSION: Our results suggest that progression of medial temporal lobe atrophy is associated with increased BBB permeability and that the transport of Abeta across the BBB is not influenced by the BBB alteration in AD.     

Acupuncture improves dendritic structure and spatial learning and memory ability of Alzheimer's disease mice

Acupuncture can improve the cognitive state of Alzheimer's disease, but its mechanism is not clear. Dendritic atrophy and synaptic loss in Alzheimer's disease brain are positively correlated with cognitive damage. Therefore, we speculated that the effect of acupuncture on improving cognitive function may be associated with reduced dendritic damage in the brain. Acupuncture at Qihai(CV6), Zhongwan(CV12), Danzhong(CV17), bilateral Zusanli(ST36), and bilateral Xuehai(SP10) acupoints was performed once a day(1-day rest after 6-day treatment) for 14 consecutive days. Senescence-accelerated mouse prone 8(SAMP8) mice without acupuncture and senescence-accelerated mouse resistant 1(SAMR1) mice were used as normal controls. After 14 days of treatment, spatial learning and memory ability of mice was assessed in each group using the Morris water maze. Dendritic changes of pyramidal cells in the hippocampal CA1 region were analyzed by quantitative Golgi staining. Our results showed that acupuncture shortened escape latency and lengthened retention time of the former platform quadrant in SAMP8 mice. Further, SAMP8 mice exhibited a significant increase in the number of apical and basal dendritic branches and total length of apical and basal dendrites after acupuncture. These results suggest that acupuncture improves spatial learning and memory ability of middle-aged SAMP8 mice by ameliorating dendritic structure.     

Role of the blood-brain barrier in the pathogenesis of Alzheimer's disease

Cerebrovascular dysfunction contributes to the cognitive decline and dementia in Alzheimer's disease (AD), and may precede cerebral amyloid angiopathy and brain accumulation of the Alzheimer's neurotoxin, amyloid beta-peptide (Abeta). The blood-brain barrier (BBB) is critical for brain Abeta homeostasis and regulates Abeta transport via two main receptors, the low density lipoprotein receptor related protein 1 (LRP1) and the receptor for advanced glycation end products (RAGE). According to the neurovascular hypothesis of AD, faulty BBB clearance of Abeta through deregulated LRP1/RAGE-mediated transport, aberrant angiogenesis and arterial dysfunction may initiate neurovascular uncoupling, Abeta accumulation, cerebrovascular regression, brain hypoperfusion and neurovascular inflammation. Ultimately these events lead to BBB compromise and chemical imbalance in the neuronal 'milieu', and result in synaptic and neuronal dysfunction. Based on the neurovascular hypothesis, we suggest an array of new potential therapeutic approaches that could be developed for AD to reduce neuroinflammation, enhance Abeta clearance and neurovascular repair, and improve cerebral blood flow. RAGE-based and LRP1-based therapeutic strategies have potential to control brain Abeta in AD, and possibly related familial cerebrovascular beta-amyloidoses. In addition, we have identified two vascularly restricted genes, GAX (growth arrest-specific homeobox), which controls LRP1 expression in brain capillaries and brain angiogenesis, and MYOCD (myocardin), which controls contractility of cerebral arterial smooth muscle cells and influences cerebral blood flow. These findings provide insights into new pathogenic pathways for the vascular dysfunction in AD and point to new therapeutic targets for AD.     

Cerebral amyloid angiopathy, blood-brain barrier disruption and amyloid accumulation in SAMP8 mice

Cerebrovascular dysfunction and β-amyloid peptide deposition on the walls of cerebral blood vessels might be an early event in the development of Alzheimer's disease. Here we studied the time course of amyloid deposition in blood vessels and blood-brain barrier (BBB) disruption in the CA1 subzone of the hippocampus of SAMP8 mice and the association between these two variables. We also studied the association between the amyloid deposition in blood vessels and the recently described amyloid clusters in the parenchyma, as well as the association of these clusters with vessels in which the BBB is disrupted. SAMP8 mice showed greater amyloid deposition in blood vessels than age-matched ICR-CD1 control mice. Moreover, at 12 months of age the number of vessels with a disrupted BBB had increased in both strains, especially SAMP8 animals. At this age, all the vessels with amyloid deposition showed BBB disruption, but several capillaries with an altered BBB showed no amyloid on their walls. Moreover, amyloid clusters showed no spatial association with vessels with amyloid deposition, nor with vessels in which the BBB had been disrupted. Finally, we can conclude that vascular amyloid deposition seems to induce BBB alterations, but BBB disruption may also be due to other factors.     

Spatial memory performance and hippocampal neuron number in osteoporotic SAMP6 mice

The senescence-accelerated mouse strain P6 (SAMP6) is an inbred mouse that represents a clinically relevant model of senile osteoporosis. However, whether osteoporotic SAMP6 mice have cognitive deficits remains largely unexplored. Here, we used Morris water maze to assess reference memory and working memory performance in SAMP6 mice and SAMR1 controls, at 4 and 8 months of age. In addition, unbiased stereological techniques were used to estimate total neuron number in hippocampal CA1 subfield of the mice used in the behavioral study. Morris water maze test revealed impairments in working memory but not in reference memory of the 4- and 8-month-old SAMP6 mice compared with the SAMR1 mice at the same age. However, there were no significant differences in the total numbers of neurons in hippocampal CA1 subfield when comparing 4-month-old SAMR1 and 4-month-old SAMP6 and 8-month-old SAMR1 and 8-month-old SAMP6, which indicate that, in SAMP6 mice, the structural correlates of working memory deficits are to be found in parameters other than the number of neurons in hippocampal CA1 subfield. These findings suggest that SAMP6 mice exhibit selective cognitive deficits and highlight the importance of this mouse model for studying the brain alterations associated with osteoporosis.     

Method for measurement of the blood-brain barrier permeability in the perfused mouse brain: application to amyloid-beta peptide in wild type and Alzheimer's Tg2576 mice

The role of transport exchanges of neuroactive solutes across the blood-brain barrier (BBB) is increasingly recognized. To take full advantage of genetically altered mouse models of neurodegenerative disorders for BBB transport studies, we adapted a brain perfusion technique to the mouse. During a carotid brain perfusion with a medium containing sheep red blood cells and mock plasma, the physiological parameters in the arterial inflow, regional cerebral blood flow (14C-iodoantipyrine autoradiography), ultrastructural integrity of the tissue, barrier to lanthanum, brain water content, energy metabolites and lactate levels remain unchanged. Amyloid-beta peptides (Abeta) were iodinated by lactoperoxidase method. Non-oxidized mono-iodinated Abeta monomers were separated by HPLC (as confirmed by MALDI-TOF spectrometry) and used in transport measurements. Transport of intact 125I-Abeta40 across the BBB was time- and concentration-dependent in contrast to negligible 14C-inulin uptake. In 5-6 months old Alzheimer's Tg2576 mice, Abeta40 BBB transport was increased by >eight-fold compared to age-matched littermate controls, and was mediated via the receptor for advanced glycation endproducts. We conclude the present arterial brain perfusion method provides strictly controlled environment in cerebral microcirculation suitable for examining transport of rapidly and slowly penetrating molecules across the BBB in normal and transgenic mice.     

Transport pathways for clearance of human Alzheimer's amyloid beta-peptide and apolipoproteins E and J in the mouse central nervous system.

Amyloid beta-peptide (Abeta) clearance from the central nervous system (CNS) maintains its low levels in brain. In Alzheimer's disease, Abeta accumulates in brain possibly because of its faulty CNS clearance and a deficient efflux across the blood-brain barrier (BBB). By using human-specific enzyme-linked immunosorbent assays, we measured a rapid 30 mins efflux at the BBB and transport via the interstitial fluid (ISF) bulk flow of human-unlabeled Abeta and of Abeta transport proteins, apolipoprotein E (apoE) and apoJ in mice. We show (i) Abeta40 is cleared rapidly across the BBB via low-density lipoprotein receptor-related protein (LRP)1 at a rate of 0.21 pmol/min g ISF or 6-fold faster than via the ISF flow; (ii) Abeta42 is removed across the BBB at a rate 1.9-fold slower compared with Abeta40; (iii) apoE, lipid-poor isoform 3, is cleared slowly via the ISF flow and across the BBB (0.03-0.04 pmol/min g ISF), and after lipidation its transport at the BBB becomes barely detectable within 30 mins; (iv) apoJ is eliminated rapidly across the BBB (0.16 pmol/min g ISF) via LRP2. Clearance rates of unlabeled and corresponding 125I-labeled Abeta and apolipoproteins were almost identical, but could not be measured at low physiologic levels by mass spectrometry. Amyloid beta-peptide 40 binding to apoE3 reduced its efflux rate at the BBB by 5.7-fold, whereas Abeta42 binding to apoJ enhanced Abeta42 BBB clearance rate by 83%. Thus, Abeta, apoE, and apoJ are cleared from brain by different transport pathways, and apoE and apoJ may critically modify Abeta clearance at the BBB.     

Beta-amyloid plaques in a model for sporadic Alzheimer's disease based on transgenic anti-nerve growth factor antibodies

Cerebral deposition of beta-amyloid (Abeta) is an invariant event of Alzheimer's disease (AD). We recently described that the brain of aged transgenic mice expressing anti-nerve growth factor (NGF) antibodies (AD11 mice) show a dramatic neurodegenerative phenotype, reminiscent of AD, which includes neuronal loss, cholinergic deficit, and tau hyperphosphorylation, associated with neurofibrillary pathology. We now report that brains of aged transgenic mice contain large amounts of beta-amyloid plaques and describe their morphology by a variety of approaches. In conclusion, the chronic deprivation of NGF leads to the formation and deposition of Abeta in AD11 mice, suggesting a direct link between NGF signaling and abnormal processing of amyloid precursor protein.     

Blood‐brain barrier damage in vascular dementia

New findings on flow or drainage pathways of brain interstitial fluid and cerebrospinal fluid have been made. The interstitial fluid flow has an effect on the passage of blood‐borne substances in the brain parenchyma, especially in areas near blood‐brain barrier (BBB)‐free regions. Actually, blood‐borne substances can be transferred in areas with intact BBB function, such as the hippocampus, the corpus callosum, periventricular areas, and medial portions of the amygdala, presumably through leaky vessels in the subfornical organs or the choroid plexus. Increasing evidence indicates that dysfunction of the BBB function may play a significant role in the pathogenesis of vascular dementia. Accordingly, we have examined which insults seen in patients suffering from vascular dementia have an effect on the BBB using experimental animal models exhibiting some phenotypes of vascular dementia. The BBB in the hippocampus was clearly deteriorated in Mongolian gerbils exposed to acute ischemia followed by reperfusion and also in stroke‐prone spontaneously hypertensive rats (SHRSP) showing hypertension. The BBB in the corpus callosum was clearly deteriorated in Wistar rats with permanent ligation of the bilateral common carotid arteries showing chronic hypoperfusion. The BBB in the hippocampus and the olfactory bulb was mildly deteriorated in aged senescence accelerated prone mice (SAMP8) showing cognitive dysfunction. The BBB in the hippocampus was mildly deteriorated in aged animals with hydrocephalus. Mild endothelial damage was seen in hyperglycemic db/db mice. In addition, mRNA expression of osteopontin, matrix metalloproteinase‐13 (MMP‐13), and CD36 was increased in vessels showing BBB damage in hypertensive SHRSP. As osteopontin, MMP‐13 and CD36 are known to be related to brain injury and amyloid β accumulation or clearance, BBB damage followed by increased gene expression of these molecules not only contributes to the pathogenesis of vascular dementia, but also bridges the gap between vascular dementia and Alzheimer's disease.     

Cognitive correlates of Abeta deposition in male and female mice bearing amyloid precursor protein and presenilin-1 mutant transgenes

Several transgenic mouse models of Alzheimer's disease (AD) have been developed that exhibit beta-amyloid (Abeta) neuropathology and behavioural deficits. However, not all studies have investigated the relationship between the development of cognitive impairment and neuropathology. Therefore, temporal changes in cognition were investigated in male and female double-mutant APPswexPS1.M146V (TASTPM) transgenic mice using an object recognition test and correlated with the development of cerebral Abeta neuropathology. Both male and female TASTPM mice exhibited similar significant cognitive impairment at 6, 8 and 10 months of age in the object recognition test, compared to wild-type littermates. There was no such cognitive impairment at 3 or 4 months of age. Quantitative immunohistochemistry using a battery of Abeta antibodies demonstrated that cerebral Abeta deposition was first apparent in 3-month-old mice, and it increased with age. The early appearance of cerebral Abeta deposits in the double-transgenic TASTPM mice supports the evidence that mutations in the PS1 gene accelerate Abeta deposition. The cerebral Abeta load was greater in female than in male TASTPM mice at all ages investigated. In the electron microscope, mature Abeta plaques comprising a fibrillar core surrounded by degenerating neurites and reactive glia were first observed in the cortex of TASTPM mice at 6 months of age, the same age at which cognitive impairment became apparent. These results suggest that the cognitive impairment in TASTPM mice is related to the disruption of neural connectivity and not simply Abeta deposition, which first occurs 3 months earlier.     

Evidence for peripheral clearance of cerebral Abeta protein following chronic,active Abeta immunization in PSAPP mice

Immunization with amyloid-beta (Abeta) peptide in mouse models of Alzheimer's disease has been reported to decrease cerebral Abeta levels and improve behavioral deficits. Several mechanisms have been proposed, including antibody-induced phagocytosis of Abeta by cerebral microglia and increased efflux of Abeta from the brain to the periphery. The latter mechanism was suggested in mice undergoing acute, passive transfer of an Abeta monoclonal antibody. Here, PSAPP transgenic mice were actively immunized by a single intraperitoneal injection of synthetic Abeta followed by chronic intranasal administration of Abeta with the mucosal adjuvant, Escherichia coli heat-labile enterotoxin, LT, twice weekly for 8 weeks. Serum from Abeta-immunized mice had an average of 240 microg/ml of anti-Abeta-specific antibodies; these antibodies had epitope(s) within Abeta1-15 and were of immunoglobulin (Ig) isotypes IgG2b, IgG2a, and IgG1. Immunization led to a 75% decrease in plaque number (P < 0.0001) and a 58% decrease in Abetax-42 levels (P < 0.026) in brain, and gliosis and neuritic dystrophy were diminished. No pathological effects of the immunization were observed in kidney, spleen, or snout. Serum Abeta levels increased 28-fold in immunized mice (53.06 ng/ml) compared to controls (1.87 ng/ml). Most of the Abeta in the serum of the immunized mice was bound to antibodies. We conclude that following active immunization, anti-Abeta antibodies sequester serum Abeta and may increase central nervous system to serum Abeta clearance.     

Progressive, age-related behavioral impairments in transgenic mice carrying both mutant amyloid precursor protein and presenilin-1 transgenes

This study provides a comprehensive behavioral characterization during aging of transgenic mice bearing both presenilin-1 (PS1) and amyloid precursor protein (APP(670,671)) mutations. Doubly transgenic mice and non-transgenic controls were evaluated at ages wherein beta-amyloid (Abeta) neuropathology in APP+PS1 mice is low (5-7 months) or very extensive (15-17 months). Progressive cognitive impairment was observed in transgenic mice for both water maze acquisition and radial arm water maze working memory. However, transgenicity did not affect Y-maze alternations, circular platform performance, standard water maze retention, or visible platform recognition at either age, nor did transgenicity affect anxiety levels in elevated plus-maze testing. In sensorimotor tasks, transgenic mice showed a progressive increase in open field activity, a progressive impairment in string agility, and an early-onset impairment in balance beam. None of these sensorimotor changes appeared to be contributory to any cognitive impairments observed, however. Non-transgenic mice showed no progressive behavioral change in any measure evaluated. Given the age-related cognitive impairments presently observed in APP+PS1 transgenic mice and their progressive Abeta deposition/neuroinflammation, Abeta neuropathology could be involved in these progressive cognitive impairments. As such, the APP+PS1 transgenic mouse offers unique opportunities to develop therapeutics to treat or prevent Alzheimer's Disease through modulation of Abeta deposition/neuroinflammation.     

Amyloid beta peptide as a vaccine for Alzheimer's disease involves receptor-mediated transport at the blood-brain barrier.

Much research is now focused on a potential vaccine for Alzheimer's disease (AD). Current studies involve administering the amyloid beta peptide (Abeta) in Freund's complete adjuvant, which cannot be used in humans. Our studies show that the immune complex of Abeta is taken up by a receptor-mediated process at the blood-brain barrier (BBB). The success of immunization for AD, therefore, may be critically dependent on circulating Abeta levels which are lower in AD patients compared to AD transgenic mice. Moreover, we have found that modifying the antibody with polyamine increases its BBB permeability and may provide a better approach to passive immunization for Alzheimer's disease.     

Amyloid beta40/42 clearance across the blood-brain barrier following intra-ventricular injections in wild-type,apoE knock-out and human apoE3 or E4 expressing transgenic mice

An important event in the pathogenesis of Alzheimer's disease (AD) is the deposition of the amyloid beta (Abeta)1-40 and 1-42 peptides in a fibrillar form, with Abeta42 typically having a greater propensity to undergo this conformational change. A major risk factor for late-onset AD is the inheritance of the apolipoprotein E (apoE) 4 allele [3,14,31]. We previously proposed that apoE may function as a "pathological chaperone" in the pathogenesis of AD (i.e. modulate the structure of Abeta, promoting or stabilizing a beta-sheet conformation), prior to the discovery of this linkage [7,40,41,42]. Data from apoE knockout / AbetaPP^(V717F) mice, has shown that the presence of apoE is necessary for cerebral amyloid formation [1,2], consistent with our hypothesis. However, in betaPP^(V717F) mice expressing human apoE3 or E4 early Abeta deposition at 9 months is suppressed, but by 15 months both human apoE expressing mice had significant fibrillar Abeta deposits with the apoE4 expressing mice having a 10 fold greater amyloid burden [8,9]. This and other data has suggested that apoE, in addition to having a facilitating role in fibril formation, may also influence clearance of Abeta peptides. In order to address if apoE affects the clearance of Abeta peptides across the blood-brain barrier (BBB) and whether there are differences in the clearance of Abeta40 versus Abeta42, we performed stereotactic, intra-ventricular micro-injections of Abeta40, Abeta42 or control peptides in wild-type, apoE knock-out (KO) or human apoE3 or apoE4 expressing transgenic mice. We found that consistent with other studies [5], Abeta40 is rapidly cleared from the brain across the BBB; however, Abeta42 is cleared much less effectively. This clearance of exogenous Abeta peptides across the BBB does not appear to be affected by apoE expression. This data suggests that Abeta42 production may favor amyloid deposition due to a reduced clearance across the BBB, compared to Abeta40. In addition, our experiments support a role of apoE as a pathological chaperone, and do not suggest an isotype specific role of apoE in exogenous Abeta peptide clearance from the CSF across the BBB.     

Temporal memory deficits in Alzheimer's mouse models: rescue by genetic deletion of BACE1

Transgenic mouse models of Alzheimer's disease (AD) exhibit amyloid-beta (Abeta) accumulation and related cognitive impairments. Although deficits in hippocampus-dependent place learning have been well characterized in Alzheimer's transgenic mice, little is known about temporal memory function in these AD models. Here, we applied trace fear conditioning to two different Alzheimer's mouse models and investigated the relationship between pathogenic Abeta and temporal memory deficits. This behavioral test requires hippocampus-dependent temporal memory processing as the conditioned and unconditioned stimuli are separated by a trace interval of 30 s. We found that both amyloid precursor protein (APP) transgenic (Tg2576) and APP/presenilin (PS)1 transgenic (Tg6799) mice were impaired in memorizing this association across the time gap. Both transgenic groups performed as well as wild-type control mice in delay fear conditioning when the trace interval was removed, indicating that the trace conditioning deficits are hippocampus-specific. Importantly, Tg6799 mice engineered to lack the major Alzheimer's beta-secretase (beta-site APP-cleaving enzyme 1: BACE1) showed behavioral rescue from temporal memory deficits. Elevated levels of soluble Abeta oligomers found in Tg6799+ mouse brains returned to wild-type control levels without changes in APP/PS1 transgene expression in BACE1-/- * Tg6799+ bigenic mouse brains, suggesting Abeta oligomers as potential mediators of memory loss. Thus, trace fear conditioning is a useful assay to test the mechanisms and therapeutic interventions for Abeta-dependent deficits in temporal associative memory. Our gene-based approach suggests that lowering soluble Abeta oligomers by inhibiting BACE1 may be beneficial for alleviating cognitive disorders in AD.