Spatiotemporal immunolocalisation of REST in the brain of healthy ageing and Alzheimer's disease rats.
ABSTRACT: In the brain, REST (Repressor Element-1 Silencing Transcription factor) is a key regulator of neuron cell-specific gene expression. Nuclear translocation of neuronal REST has been shown to be neuroprotective in a healthy ageing context. In contrast, inability to upregulate nuclear REST is thought to leave ageing neurons vulnerable to neurodegenerative stimuli, such as Alzheimer's disease (AD) pathology. Hippocampal and cortical neurons are known to be particularly susceptible to AD-associated neurodegeneration. However, REST expression has not been extensively characterised in the healthy ageing brain. Here, we examined the spatiotemporal immunolocalisation of REST in the brains of healthy ageing wild-type Fischer-344 and transgenic Alzheimer's disease rats (TgF344-AD). Nuclear expression of REST increased from 6 months to 18 months of age in the hippocampus, frontal cortex and subiculum of wild-type rats, but not in TgF344-AD rats. No changes in REST were measured in more posterior cortical regions or in the thalamus. Interestingly, levels of the presynaptic marker synaptophysin, a known gene target of REST, were lower in CA1 hippocampal neurons of 18-month TgF344-AD rats compared to 18-month wild-types, suggesting that elevated nuclear REST may protect against synapse loss in the CA1 of 18-month wild-type rats. High REST expression in ageing wild-type rats did not, however, protect against axonal loss nor against astroglial reactivity in the hippocampus. Taken together, our data confirm that changes in nuclear REST expression are context-, age- and brain region-specific. Moreover, key brain structures involved in learning and memory display elevated REST expression in healthy ageing wild-type rats but not TgF344-AD rats.
Project description:Alzheimer's disease (AD) is a progressive neurodegenerative disease resulting in cognitive decline. A unique rat model, TgF344-AD, recapitulates pathological hallmarks of AD. We used a longitudinal design to address the timing of expression of behavioral phenotypes in male and female TgF344-AD rats. In both sexes, we confirmed an age-dependent buildup of amyloid-?. In the open field, female, but not male, TgF344-AD rats were hypoactive at 6 and 12 months of age but at 18 months the two genotypes were similar in levels of activity response. Both male and female TgF344-AD rats had a deficit in performance on a learning and memory task. Male TgF344-AD, but not female, rats had evidence of hyposmia regardless of age. Rest-activity rhythms followed the typical active/inactive phase in all rats regardless of genotype or age. In males, home cage activity was similar across age and genotype; in females, regardless of genotype animals were less active as they aged. These changes highlight some behavioral markers of disease in the rat model. Early markers of disease may be important in early diagnosis and assessment of efficacy when treatment becomes available.
Project description:BACKGROUND:In addition to cognitive deficits, Alzheimer's disease (AD) is associated with other neuropsychiatric symptoms, including severe depression. Indeed, depression often precedes cognitive deficits in patients with AD. Unfortunately, the field has seen only minimal therapeutic advances, underscoring the critical need for new treatments. P7C3 aminopropyl carbazoles promote neuronal survival by enhancing nicotinamide adenine dinucleotide flux in injured neurons. Neuroprotection with P7C3 compounds has been demonstrated in preclinical models of neurodegeneration by virtue of promoting neuronal survival independently of early disease-specific pathology, resulting in protection from cognitive deficits and depressive-like behavior. We hypothesize that P7C3 compounds might be uniquely applicable to patients with AD, given the comorbid presentation of depression and cognitive deficits. METHODS:Aging male and female wild-type and TgF344-AD rats, a well-characterized preclinical AD model, were administered (-)-P7C3-S243 daily for 9 and 18 months, beginning at 6 months of age. Behavioral phenotypes related to cognition and depression were assessed at 15 and 24 months, and brain pathology and biochemistry were assessed at 24 months. RESULTS:(-)-P7C3-S243 safely protected aging male and female wild-type and TgF344-AD rats from cognitive deficits and depressive-like behavior. Depressive-like behavior occurred earlier than cognitive deficits in TgF344-AD rats, consistent with AD in many patients. Treatment with (-)-P7C3-S243 blocked neurodegeneration in TgF344-AD rats, without altering amyloid deposition or indicators of neuroinflammation. CONCLUSIONS:Neuronal cell death-specific treatment approaches, such as P7C3 compounds, may represent a new treatment approach for patients experiencing the combination of cognitive deficits and depression associated with AD.
Project description:Current findings suggest that accumulation of amyloid-? (A?) and hyperphosphorylated tau in the brain disrupt synaptic function in hippocampal-cortical neuronal networks leading to impairment in cognitive and affective functions in Alzheimer's disease (AD). Development of new disease-modifying AD drugs are challenging due to the lack of predictive animal models and efficacy assays. In the present study we recorded neural activity in TgF344-AD rats, a transgenic model with a full array of AD pathological features, including age-dependent A? accumulation, tauopathy, neuronal loss, and cognitive impairments. Under urethane anesthesia, TgF344-AD rats showed significant age-dependent decline in brainstem-elicited hippocampal theta oscillation and decreased theta-phase gamma-amplitude coupling comparing to their age-matched wild-type counterparts. In freely-behaving condition, the power of hippocampal theta oscillation and gamma power during sharp-wave ripples were significantly lower in TgF344-AD rats. Additionally, these rats showed impaired coherence in both intercortical and hippocampal-cortical network dynamics, and increased incidence of paroxysmal high-voltage spindles, which occur during awake, behaviorally quiescent state. TgF344-AD rats demonstrated impairments in sensory processing, having diminished auditory gating and 40-Hz auditory evoked steady-state response. The observed differences in neurophysiological activities in TgF344-AD rats, which mirror several abnormalities described in AD patients, may be used as promising markers to monitor disease-modifying therapies.
Project description:A better and non-invasive characterization of the preclinical phases of Alzheimer's disease (AD) is important to advance its diagnosis and obtain more effective benefits from potential treatments. The TgF344-AD rat model has been well characterized and shows molecular, behavioral and brain connectivity alterations that resemble the silent period of the pathology. Our aim was to longitudinally investigate functional brain connectivity in established resting-state networks (RSNs) obtained by independent component analysis (ICA) in a cohort of TgF344-AD and control rats every 3 months, from 5 to 18 months of age, to cover different stages of the disease. Before each acquisition, working memory performance was evaluated by the delayed non match-to-sample (DNMS) task. Differences in the temporal evolution were observed between groups in the amplitude and shape of the somatosensorial and sensorimotor networks but not in the whole default mode network (DMN). Subsequent high dimensional ICA analysis showed early alterations in the anterior DMN subnetwork activity of TgF344-AD rats compared to controls. Performance of DNMS task was positively correlated with somatosensorial network at 5 months of age in the wild-type (WT) animals but not in the Tg-F344 rats. At different time points, DMN showed negative correlation with cognitive performance in the control group while in the transgenic group the correlation was positive. In addition, behavioral differences observed at 5 months of age correlated with alterations in the posterior DMN subnetwork. We have demonstrated that functional connectivity using ICA represents a useful biomarker also in animal models of AD such as the TgF344AD rats, as it allows the identification of alterations associated with the progression of the disease, detecting differences in specific networks even at very early stages.
Project description:Spatial navigation is impaired in early stages of Alzheimer's disease, and may be a defining behavioral marker of preclinical AD. A new rat model (TgF344-AD) of AD overcomes many limitations of other rodent models, though spatial navigation has not been comprehensively assessed. Using the hidden and cued platform variants of the Morris water task, a longitudinal assessment of spatial navigation was conducted on TgF344-AD (n?=?16) and Fischer 344 (n?=?12) male and female rats at three age ranges: 4 to 5 months, 7 to 8, and 10 to 11 months of age. TgF344-AD rats exhibited largely intact navigation at 4-5 months, with deficits in the hidden platform task emerging at 7-8 months and becoming significantly pronounced at 10-11 months of age. In general, TgF344-AD rats displayed less accurate swim trajectories to the platform and searched a wider area around the platform region compared to wildtype rats. Impaired navigation occurred in the absence of deficits in acquiring the procedural task demands or navigation to the cued platform location. Together, the results indicate that TgF344-AD rats exhibit comparable navigational deficits to those found in individuals with preclinical-AD.
Project description:Decades of research attempting to slow the onset of Alzheimer's disease (AD) indicates that a better understanding of memory will be key to the discovery of effective therapeutic approaches. Here, we ask whether prodromal neural network dysfunction might occur in the hippocampal trisynaptic circuit by using α5IA (an established memory enhancer and selective negative allosteric modulator of extrasynaptic tonically active α5GABA-A receptors) as a probe drug in TgF344-AD transgenic rats, a model for β-amyloid induced early onset AD. The results demonstrate that orally bioavailable α5IA increases CA1 pyramidal cell mean firing rates during foraging and peak ripple amplitude during wakeful immobility in <i>wild type</i> F344 rats in a familiar environment. We further demonstrate that CA1 ripples in TgF344-AD rats are nonresponsive to α5IA by 9 months of age, prior to the onset of AD-like pathology and memory dysfunction. TgF344-AD rats express human β-amyloid precursor protein (with the Swedish mutation) and human presenilin-1 (with a Δ exon 9 mutation) and we found high serum Aβ42 and Aβ40 levels by 3 months of age. When taken together, this demonstrates, to the best of our knowledge, the first evidence for prodromal α5GABA-A receptor dysfunction in the ripple-generating hippocampal trisynaptic circuit of AD-like transgenic rats. As α5GABA-A receptors are found at extrasynaptic and synaptic contacts, we posit that negative modulation of α5GABA-A receptor mediated tonic as well as phasic inhibition augments CA1 ripples and memory consolidation but that this modulatory mechanism is lost at an early stage of AD onset.
Project description:The research of Alzheimer's disease (AD) in its early stages and its progression till symptomatic onset is essential to understand the pathology and investigate new treatments. Animal models provide a helpful approach to this research, since they allow for controlled follow-up during the disease evolution. In this work, transgenic TgF344-AD rats were longitudinally evaluated starting at 6 months of age. Every 3 months, cognitive abilities were assessed by a memory-related task and magnetic resonance imaging (MRI) was acquired. Structural and functional brain networks were estimated and characterized by graph metrics to identify differences between the groups in connectivity, its evolution with age, and its influence on cognition. Structural networks of transgenic animals were altered since the earliest stage. Likewise, aging significantly affected network metrics in TgF344-AD, but not in the control group. In addition, while the structural brain network influenced cognitive outcome in transgenic animals, functional network impacted how control subjects performed. TgF344-AD brain network alterations were present from very early stages, difficult to identify in clinical research. Likewise, the characterization of aging in these animals, involving structural network reorganization and its effects on cognition, opens a window to evaluate new treatments for the disease.
Project description:Alzheimer's disease (AD) pathology begins decades prior to onset of clinical symptoms, and the entorhinal cortex and hippocampus are among the first and most extensively impacted brain regions. The TgF344-AD rat model, which more fully recapitulates human AD pathology in an age-dependent manner, is a next generation preclinical rodent model for understanding pathophysiological processes underlying the earliest stages of AD (Cohen et al., 2013). Whether synaptic alterations occur in hippocampus prior to reported learning and memory deficit is not known. Furthermore, it is not known if specific hippocampal synapses are differentially affected by progressing AD pathology, or if synaptic deficits begin to appear at the same age in males and females in this preclinical model. Here, we investigated the time-course of synaptic changes in basal transmission, paired-pulse ratio, as an indirect measure of presynaptic release probability, long-term potentiation (LTP), and dendritic spine density at two hippocampal synapses in male and ovariectomized female TgF344-AD rats and wildtype littermates, prior to reported behavioral deficits. Decreased basal synaptic transmission begins at medial perforant path-dentate granule cell (MPP-DGC) synapses prior to Schaffer-collateral-CA1 (CA3-CA1) synapses, in the absence of a change in paired-pulse ratio (PPR) or dendritic spine density. N-methyl-d-aspartate receptor (NMDAR)-dependent LTP magnitude is unaffected at CA3-CA1 synapses at 6, 9, and 12months of age, but is significantly increased at MPP-DGC synapses in TgF344-AD rats at 6months only. Sex differences were only observed at CA3-CA1 synapses where the decrease in basal transmission occurs at a younger age in males versus females. These are the first studies to define presymptomatic alterations in hippocampal synaptic transmission in the TgF344-AD rat model. The time course of altered synaptic transmission mimics the spread of pathology through hippocampus in human AD and provides support for this model as a valuable preclinical tool in elucidating pathological mechanisms of early synapse dysfunction in AD.
Project description:Alzheimer's disease (AD), pathologically characterized by amyloid-? peptide (A?) accumulation, neurofibrillary tangle formation, and neurodegeneration, is thought to involve early-onset neurovascular abnormalities. Hitherto studies on AD-associated neurovascular injury have used animal models that exhibit only a subset of AD-like pathologies and demonstrated some A?-dependent vascular dysfunction and destabilization of neuronal network. The present work focuses on the early stage of disease progression and uses TgF344-AD rats that recapitulate a broader repertoire of AD-like pathologies to investigate the cerebrovascular and neuronal network functioning using in situ two-photon fluorescence microscopy and laminar array recordings of local field potentials, followed by pathological analyses of vascular wall morphology, tau hyperphosphorylation, and amyloid plaques. Concomitant to widespread amyloid deposition and tau hyperphosphorylation, cerebrovascular reactivity was strongly attenuated in cortical penetrating arterioles and venules of TgF344-AD rats in comparison to those in non-transgenic littermates. Blood flow elevation to hypercapnia was abolished in TgF344-AD rats. Concomitantly, the phase-amplitude coupling of the neuronal network was impaired, evidenced by decreased modulation of theta band phase on gamma band amplitude. These results demonstrate significant neurovascular network dysfunction at an early stage of AD-like pathology. Our study identifies early markers of pathology progression and call for development of combinatorial treatment plans.
Project description:<b>Background: </b>In vivo PET/SPECT imaging of neuroinflammation is primarily based on the estimation of the 18?kDa-translocator-protein (TSPO). However, TSPO is expressed by different cell types which complicates the interpretation.<br><br><b>Objective: </b>The present study evaluates the cellular origin of TSPO alterations in Alzheimer's disease (AD).<br><br><b>Methods: </b>The TSPO cell origin was evaluated by combining radioactive imaging approaches using the TSPO radiotracer [125I]CLINDE and fluorescence-activated cell sorting, in a rat model of AD (TgF344-AD) and in AD subjects.<br><br><b>Results: </b>In the hippocampus of TgF344-AD rats, TSPO overexpression not only concerns glial cells but the increase is visible at 12 and 24 months in astrocytes and only at 24 months in microglia. In the temporal cortex of AD subjects, TSPO upregulation involved only glial cells. However, the mechanism of this upregulation appears different with an increase in the number of TSPO binding sites per cell without cell proliferation in the rat, and a microglial cell population expansion with a constant number of binding sites per cell in human AD.<br><br><b>Conclusion: </b>These data indicate an earlier astrocyte intervention than microglia and that TSPO in AD probably is an exclusive marker of glial activity without interference from other TSPO-expressing cells. This observation indicates that the interpretation of TSPO imaging depends on the stage of the pathology, and highlights the particular role of astrocytes.