GLT-1 loss accelerates cognitive deficit onset in an Alzheimer's disease animal model.
ABSTRACT: Glutamate transporters regulate normal synaptic network interactions and prevent neurotoxicity by rapidly clearing extracellular glutamate. GLT-1, the dominant glutamate transporter in the cerebral cortex and hippocampus, is significantly reduced in Alzheimer's disease (AD). However, the role GLT-1 loss plays in the cognitive dysfunction and pathology of AD is unknown. To determine the significance of GLT-1 dysfunction on AD-related pathological processes, mice lacking one allele for GLT-1(+/-) were crossed with transgenic mice expressing mutations of the amyloid-? protein precursor and presenilin-1 (A?PPswe/PS1?E9) and investigated at 6 or 9 months of age. Partial loss of GLT-1 unmasked spatial memory deficits in 6-month-old mice expressing A?PPswe/PS1?E9, with these mice also exhibiting an increase in the ratio of detergent-insoluble A?42/A?40. At 9 months both behavioral performance and insoluble A?42/A?40 ratios among GLT-1(+/+)/A?PPswe/PS1?E9 and GLT-1(+/-)/A?PPswe/PS1?E9 mice were comparable. These results suggest that deficits in glutamate transporter function compound the effects of familial AD A?PP/PS1 mutant transgenes in younger animals and thus may contribute to early occurring pathogenic processes associated with AD.
Project description:Objective:Glutamate transporter-1 (GLT-1) and system x c - mediate glutamate uptake and release, respectively. Ceftriaxone has been reported to upregulate GLT-1 expression and improve cognitive decline in APP/PS1 mice. The aim of the present study was to elucidate the role of GLT-1 in ceftriaxone-mediated improvement on cognitive deficits and associated changes in xCT (catalytic subunit of system x c -) expression and activity using GLT-1 knockdown APP/PS1 mice. Methods:GLT-1 knockdown (GLT-1±) mice were generated in C57BL/6J mice using the CRISPR/Cas9 technique and crossed to APP/PS1 mice to generate GLT-1±APP/PS1 mice. The cognition was evaluated by novel object recognition and Morris water maze tests. GLT-1 and xCT expression, GLT-1 uptake for glutamate, and glutathione levels of hippocampus were assayed using Western blot and immunohistochemistry, 3H-glutamate, and glutathione assay kit, respectively. Results:In comparison with wild-type mice, APP/PS1 mice exhibited significant cognitive deficits, represented with poor performance in novel object recognition and Morris water maze tests, downregulated GLT-1 expression and glutamate uptake. Ceftriaxone treatment significantly improved the above impairments in APP/PS1 mice, but had negligible impact in GLT-1±APP/PS1 mice. The xCT expression increased in APP/PS1 and GLT-1±APP/PS1 mice. This upregulation might be a compensatory change against the accumulated glutamate resulting from GLT-1 impairment. Ceftriaxone treatment restored xCT expression in APP/PS1 mice, but not in GLT-1±APP/PS1 mice. Glutathione levels decreased in APP/PS1 mice in comparison to the wild-type group. After ceftriaxone administration, the decline in glutathione level was restored in APP/PS1 mice, but not in GLT-1±APP/PS1 mice. Conclusion:Ceftriaxone improves cognitive impairment of APP/PS1 mice by upregulating GLT-1-mediated uptake of glutamate and co-regulation of GLT-1 and xCT in APP/PS1 mice.
Project description:A hallmark of Alzheimer disease (AD) is the deposition of amyloid ? (A?) in brain parenchyma and cerebral blood vessels, accompanied by cognitive decline. Previously, we showed that human apolipoprotein A-I (apoA-I) decreases A?(40) aggregation and toxicity. Here we demonstrate that apoA-I in lipidated or non-lipidated form prevents the formation of high molecular weight aggregates of A?(42) and decreases A?(42) toxicity in primary brain cells. To determine the effects of apoA-I on AD phenotype in vivo, we crossed APP/PS1?E9 to apoA-I(KO) mice. Using a Morris water maze, we demonstrate that the deletion of mouse Apoa-I exacerbates memory deficits in APP/PS1?E9 mice. Further characterization of APP/PS1?E9/apoA-I(KO) mice showed that apoA-I deficiency did not affect amyloid precursor protein processing, soluble A? oligomer levels, A? plaque load, or levels of insoluble A? in brain parenchyma. To examine the effect of Apoa-I deletion on cerebral amyloid angiopathy, we measured insoluble A? isolated from cerebral blood vessels. Our data show that in APP/PS1?E9/apoA-I(KO) mice, insoluble A?(40) is increased more than 10-fold, and A?(42) is increased 1.5-fold. The increased levels of deposited amyloid in the vessels of cortices and hippocampi of APP/PS1?E9/apoA-I(KO) mice, measured by X-34 staining, confirmed the results. Finally, we demonstrate that lipidated and non-lipidated apoA-I significantly decreased A? toxicity against brain vascular smooth muscle cells. We conclude that lack of apoA-I aggravates the memory deficits in APP/PS1?E9 mice in parallel to significantly increased cerebral amyloid angiopathy.
Project description:Alzheimer's disease (AD) pathology occurs in part as the result of excessive production of ?-amyloid (A?). Metabotropic glutamate receptor 5 (mGluR5) is now considered a receptor for A? and consequently contributes to pathogenic A? signaling in AD.Genetic deletion of mGluR5 rescues the spatial learning deficits observed in APPswe/PS1?E9 AD mice. Moreover, both A? oligomer formation and A? plaque number are reduced in APPswe/PS1?E9 mice lacking mGluR5 expression. In addition to the observed increase in A? oligomers and plaques in APPswe/PS1?E9 mice, we found that both mTOR phosphorylation and fragile X mental retardation protein (FMRP) expression were increased in these mice. Genetic deletion of mGluR5 reduced A? oligomers, plaques, mTOR phosphorylation and FMRP expression in APPswe/PS1?E9 mice.Thus, we propose that A? activation of mGluR5 appears to initiate a positive feedback loop resulting in increased A? formation and AD pathology in APPswe/PS1?E9 mice via mechanism that is regulated by FMRP.
Project description:Neuronal hyperactivity is one of the earliest events observed in Alzheimer's disease (AD). Moreover, alterations in the expression of glutamate transporters have been reported to exacerbate amyloid pathology and cognitive deficits in transgenic AD mouse models. However, the molecular links between these pathophysiological changes remain largely unknown. Here, we report novel interaction between presenilin 1 (PS1), the catalytic component of the amyloid precursor protein-processing enzyme, ?-secretase, and a major glutamate transporter-1 (GLT-1). Our data demonstrate that the interaction occurs between PS1 and GLT-1 expressed at their endogenous levels in vivo and in vitro, takes place in both neurons and astrocytes, and is independent of the PS1 autoproteolysis and ?-secretase activity. This intriguing discovery may shed light on the molecular crosstalk between the proteins linked to the maintenance of glutamate homeostasis and A? pathology.
Project description:Metabotropic glutamate receptor 5 (mGluR5) has been implicated in Alzheimer's disease (AD) pathology. We sought to understand whether mGluR5's role in AD requires glutamate signaling. We used a potent mGluR5 silent allosteric modulator (SAM, BMS-984923) to separate its well-known physiological role in glutamate signaling from a pathological role in mediating amyloid-? oligomer (A?o) action. Binding of the SAM to mGluR5 does not change glutamate signaling but strongly reduces mGluR5 interaction with cellular prion protein (PrPC) bound to A?o. The SAM compound prevents A?o-induced signal transduction in brain slices and in an AD transgenic mouse model, the APPswe/PS1?E9 strain. Critically, 4 weeks of SAM treatment rescues memory deficits and synaptic depletion in the APPswe/PS1?E9 transgenic mouse brain. Our data show that mGluR5's role in A?o-dependent AD phenotypes is separate from its role in glutamate signaling and silent allosteric modulation of mGluR5 has promise as a disease-modifying AD intervention with a broad therapeutic window.
Project description:Senescence-accelerated mouse prone 8 strain (SAMP8) and PrP-hA?PPswe/PS1?E9 (APP/PS1) mice are classic animal models of sporadic Alzheimer's disease and familial AD respectively. Our study showed that object recognition memory, spatial learning and memory, active and passive avoidance were deteriorated and neuroendocrine immunomodulation (NIM) network was imbalance in SAMP8 and APP/PS1 mice. SAMP8 and APP/PS1 mice had their own specific phenotype of cognition, neuroendocrine, immune and NIM molecular network. The endocrine hormone corticosterone, luteinizing hormone and follicle-stimulating hormone, chemotactic factor monocyte chemotactic protein-1, macrophage inflammatory protein-1?, regulated upon activation normal T cell expressed and secreted factor and eotaxin, pro-inflammatory factor interleukin-23, and the Th1 cell acting as cell immunity accounted for cognitive deficiencies in SAMP8 mice, while adrenocorticotropic hormone and gonadotropin-releasing hormone, colony stimulating factor granulocyte colony stimulating factor, and Th2 cell acting as humoral immunity in APP/PS1 mice. On the pathway level, chemokine signaling and T cell receptor signaling pathway played the key role in cognition impairments of two models, while cytokine-cytokine receptor interaction and natural killer cell mediated cytotoxicity were more important in cognitive deterioration of SAMP8 mice than APP/PS1 mice. This mechanisms of NIM network underlying cognitive impairment is significant for further understanding the pathogenesis of AD and can provide useful information for development of AD therapeutic drug.
Project description:Despite compelling evidence that the accumulation of amyloid-beta (A?) promotes neocortical MAPT (tau) aggregation in familial and idiopathic Alzheimer's disease (AD), murine models of cerebral amyloidosis are not considered to develop tau-associated pathology. In the present study, we show that tau can accumulate spontaneously in aged transgenic APPswe/PS1?E9 mice. Tau pathology is abundant around A? deposits, and further characterized by accumulation of Gallyas and thioflavin-S-positive inclusions, which were detected in the APPswe/PS1?E9 brain at 18 months of age. Age-dependent increases in argyrophilia correlated positively with binding levels of the paired helical filament (PHF) tracer [18F]Flortaucipir, in all brain areas examined. Sarkosyl-insoluble PHFs were visualized by electron microscopy. Quantitative proteomics identified sequences of hyperphosphorylated and three-repeat tau in transgenic mice, along with signs of RNA missplicing, ribosomal dysregulation and disturbed energy metabolism. Tissue from the frontal gyrus of human subjects was used to validate these findings, revealing primarily quantitative differences between the tau pathology observed in AD patient vs. transgenic mouse tissue. As physiological levels of endogenous, 'wild-type' tau aggregate secondarily to A? in APPswe/PS1?E9 mice, this study suggests that amyloidosis is both necessary and sufficient to drive tauopathy in experimental models of familial AD.
Project description:AIM:Alzheimer's disease (AD) is largely considered a neuron-derived insult, but also involves failure of astroglia. A recent study indicated that mutated presenilin 1 (PS1M146V), a putative endoplasmic reticulum (ER) Ca2+ channel with decreased Ca2+ conductance, impairs the traffic of astroglial peptidergic vesicles. Whether other pathogenically relevant PS1 mutants, such as PS1?E9, which code for ER channel with putative increased Ca2+ conductance, similarly affect vesicle traffic, is unknown. METHODS:Here, we cotransfected rat astrocytes with plasmids encoding mutant PS1?E9 and atrial natriuretic peptide or vesicular glutamate transporter 1 tagged with fluorescent proteins (pANP.emd or pVGLUT1-EGFP respectively), to microscopically examine whether alterations in vesicle mobility and Ca2+ -regulated release of gliosignalling molecules manifest as a general vesicle-based defect; control cells were transfected to co-express exogenous or native wild-type PS1 and pANP.emd or pVGLUT1-EGFP. The vesicle mobility was analysed at rest and after ATP stimulation that increased intracellular calcium activity. RESULTS:In PS1?E9 astrocytes, spontaneous mobility of both vesicle types was reduced (P < .001) when compared to controls. Post-stimulatory recovery of fast vesicle mobility was hampered in PS1?E9 astrocytes. The ATP-evoked peptide release was less efficient in PS1?E9 astrocytes than in the controls (P < .05), as was the pre-stimulatory mobility of these vesicles. CONCLUSION:Although the PS1 mutants PS1M146V and PS1?E9 differently affect ER Ca2+ conductance, our results revealed a common, vesicle-type indiscriminate trafficking defect in PS1?E9 astrocytes, indicating that reduced secretory vesicle-based signalling is a general deficit in AD astrocytes.
Project description:The transmembrane protein CD33 is a sialic acid-binding immunoglobulin-like lectin that regulates innate immunity but has no known functions in the brain. We have previously shown that the CD33 gene is a risk factor for Alzheimer's disease (AD). Here, we observed increased expression of CD33 in microglial cells in AD brain. The minor allele of the CD33 SNP rs3865444, which confers protection against AD, was associated with reductions in both CD33 expression and insoluble amyloid beta 42 (A?42) levels in AD brain. Furthermore, the numbers of CD33-immunoreactive microglia were positively correlated with insoluble A?42 levels and plaque burden in AD brain. CD33 inhibited uptake and clearance of A?42 in microglial cell cultures. Finally, brain levels of insoluble A?42 as well as amyloid plaque burden were markedly reduced in APP(Swe)/PS1(?E9)/CD33(-/-) mice. Therefore, CD33 inactivation mitigates A? pathology and CD33 inhibition could represent a novel therapy for AD.
Project description:Alzheimer's disease (AD) is a devastating illness characterized by a progressive loss of cognitive, social, and emotional functions, including memory impairments and more global cognitive deficits. Clinical-epidemiological evidence suggests that neuropsychiatric symptoms precede the onset of cognitive symptoms both in humans with early and late onset AD. The behavioural profile promoted by the AD pathology is believed to associate with degeneration of the serotonergic system. Using the APPswe/PS1?E9 model of AD-like pathology starting with 9 months old mice, we characterised long term non-cognitive behavioural changes measured at 9, 12, 15, and 18 months of age and applied principal component analysis on data obtained from open field, elevated plus maze, and social interaction tests. Long-term treatment with the selective serotonin reuptake inhibitor (SSRI) paroxetine was applied to assess the role of 5-HT on the behavioural profile; duration of treatment was 9 months, initiated when mice were 9 months of age. Treatment with paroxetine delays the decline in locomotion, in exploration and risk assessment behaviour, found in the APP/PS1 mice. APP/PS1 mice also exhibit low social activity and less aggressiveness, both of which are not affected by treatment with paroxetine. The APP/PS1 behavioural phenotype, demonstrated in this study, only begins to manifest itself from 12 months of age. Our results indicate that treatment with SSRI might ameliorate some of the behavioural deficits found in aged APP/PS1 mice.