Unknown,Transcriptomics,Genomics,Proteomics

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Altered gene expression is associated with age-dependent memory impairment

ABSTRACT: The mechanisms underlying age-associated memory impairment are not well understood. We have shown that the onset of memory disturbances in the aging brain is associated with altered hippocampal chromatin plasticity. During learning, aged mice display a specific deregulation of histone H4 lysine 12 (H4K12) acetylation. To analyze if deregulated H4K12 acetylation impacts on learning-induced gene-expression required for memory consolidation we performed a high-density oligonucleotide microarray to compare the entire hippocampal gene-expression profile of 3 and 16-month-old mice during memory consolidation. In order to identify genes differentially regulated between 3- and 16-month old mice upon fear conditioning we subjected 3- and 16-month old mice to fear conditioning (4 mice each group, total 8 mice) . Mice of the same age that were handled but not subjected to any of the employed behavior paradigms served as control (4 mice 3-month old and 4 mice 16-month old, total 8 mice). During fear conditioning mice are subjected to a novel context followed by a mild electric foot-shock (context-shock exposure). In order to identify genes that are differentially regulated upon fear conditioning and are specific to associative learning we also tested the hippocampal gene-expression profile of 3-month old mice subjected to the same context-exposure that is not followed by a foot-shock (Context-exposure) (4 mice) or receive an immediate foot shock once they are placed in the context and only afterwards are allowed to explore the context (shock-context exposure) (4 mice). In order to identify genes that are regulated upon fear conditioning and are specific to associative learning we compared the hippocampal gene-expression profile of mice subjected to fear conditioning (context-shock), context or shock-context exposure regarding to their age-matched control mice (3 month old) mentioned above (control). Hippocampi from each mice were tested resulting to 24 samples which were separately hybridized (OneColor Array Design).

ORGANISM(S): Mus musculus

SUBMITTER: Athanasios Zovoilis

PROVIDER: E-GEOD-20270 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Extinction learning refers to the phenomenon that a previously learned response to an environmental stimulus, for example the expression of an aversive behavior upon exposure to a specific context, is reduced when the stimulus is repeatedly presented in the absence of a previously paired aversive event. Extinction of fear memories has been implicated with the treatment of anxiety disease but the molecular processes that underlie fear extinctionare only beginning to emerge. Here we show that fear extinction initiates up-regulation of hippocampal insulin-growth factor 2 (Igf2) and down-regulation of insulin-growth factor binding protein 7 (Igfbp7). In line with this observation we demonstrate that IGF2 facilitates fear extinction, while IGFBP7 impairs fear extinction in an IGF2-dependent manner. Furthermore, we identify one cellular substrate of altered IGF2-signaling during fear extinction. To this end we show that fear extinction-induced IGF2/IGFBP7-signaling promotes the survival of 17-19 day-old newborn hippocampal neurons. In conclusion, our data suggests that therapeutic strategies that enhance IGF2-signaling and adult neurogenesis might be suitable to treat disease linked to excessive fear memory. We employed mice to investigate fear extinction in the hippocampus-dependent contextual fear conditioning paradigm. To this end, male C57BL/6J mice were exposed to the fear conditioning box (context) followed by an electric foot-shock which elicits the acquisition of conditioned contextual fear. For extinction training animals were repeatedly reexposed to the conditioned context on consecutive days (24h interval) without receiving the footshockagain (extinction trial, E). This procedure eventually results in the decline of the aversive freezing behavior. Mice that were exposed to the conditioning context without receiving fear conditioning training served as control groups. To gain a better understanding of the molecular processes underlying fear extinction we performed a genome-wide analysis of the hippocampal transcriptome during fear extinction. In the employed paradigm fear extinction is a gradual process. To capture the longitudinal course of fear extinction we decided to perform hippocampal microarray analysis at two time points: (1) After the first extinction trial (E1) when animals display high levels of aversive freezing behavior and (2) at the extinction trial on which the freezing behavior was significantly reduced when compared to E1. This extinction trial, in the case of this experiment E5, we termed “extinction trial low freezing” (ELF). Mice that were exposed to the conditioning context without receiving fear conditioning training served as control groups (3). For all three groups we hybridized 5 samples (biological replicates).

Project description:Here we tested a hypothesis that epileptogenesis influences expression pattern of genes in the basolateral amygdala that are critical for fear conditioning. Whole genome molecular profiling of basolateral rat amygdala was performed to compare the transcriptome changes underlying fear learning in epileptogenic and control animals. Our analysis revealed that after acquisition of fear conditioning 26 genes were regulated differently in the basolateral amygdala of both groups. Thus, our study provides the first evidence that not only the damage to the neuronal pathways but also altered composition or activity level of molecular machinery responsible for formation of emotional memories within surviving pathways can contribute to impairment in emotional learning in epileptogenic animals. Understanding the function of those genes in emotional learning provides an attractive avenue for identification of novel drug targets for treatment of emotional disorders after epileptogenesis-inducing insult. Experiment Overall Design: Experiment description: Experiment Overall Design: Array: Rat Genome 230-2.0 (Affymetrix). Experiment Overall Design: Samples: 2 biological replicates from 4 experimental groups (control unpaired = CU, CU1, control paired = CP, CP1, epileptogenic unpaired = EU, EU1, epileptogenic paired = EP, EP1). Experiment Overall Design: Animals&model: Amygdala stimulation model (Nissinen et al., 2000): Experiment Overall Design: control (C) animals = operated, not stimulated; Experiment Overall Design: epileptogenic (E) animals = stimulated, responded with "good" status epilepticus (at least 40HAFDs within first 3h of SE), not expressing spontaneous seizures through the whole study. Experiment Overall Design: All animals received 5 habituation session to the fear conditioning apparatus lasting 10 min, starting on day 5 (2 sessions on day 5 and 6 and 1 session on day 7) after stimulation (induction of SE). Experiment Overall Design: On 8th day after stimulation: Experiment Overall Design: unpaired (U) = twice received: 2min in apparatus â footshock (1.5mA, 1s)â tone (75dB for 20 sec) Experiment Overall Design: paired (P) = twice received: 2min in apparatus â tone (75dB for 20 sec) co-terminated by footshock (1.5mA, 1s). Experiment Overall Design: RNA isolation: decapitation â ipsilateral temporal lobe isolated, embed in OCT and frozen in -70C. Cut into 10Âµm sections, thionin stained (Ambion protocol), basal and lateral nuclei of the amygdala laser-microdissected; total cellular RNA isolated with PicoPure RNA isolation kit (Arcturus). Experiment Overall Design: RNA amplification: 30ng of of total cellular RNA from each rat underwent of 2 rounds of amplification using MessageAmp II aRNA kit (Ambion), according to manufacturer protocol (in vitro transcription time 14h in both rounds). Experiment Overall Design: Sample pooling: aRNA from 2 animals was pooled (10Âµg in total = 2x5Âµg) and 8 samples were labeled and hybridized: CP, CP1, CU, CU1, EP, EP1, EU, EU1; (altogether aRNA from 16 rats was used).

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Altered gene expression is associated with age-dependent memory impairment

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