National Institute on Aging (RO1AG037984, RO1AG036800, RO1AG049711, and RO1AG052258), - PowerPoint Presentation

1. National Institute on Aging (RO1AG037984, RO1AG036800, RO1AG049711, and RO1AG052258), and by the Evelyn F. McKnight Brain Research Foundation. The beacon discrimination task appears sensitive to age-related spatial PS decline in middle-age rats.The DG showed the greatest transcriptomic changes with age, and featured the greatest number of genes that correlated with spatial PS and reference memory of all hippocampal tissues studied.Animals with impaired spatial PS exhibited better reference memory, downregulation of synaptic and neurogenesis-related genes; and upregulation of mRNA processing genes in the DG. CA1 and CA3 showed relatively fewer changes with cognition.Combined behavior and transcription results may suggest a divergence of cognitive strategies with age, potentially in response to changes in neural function and gene expression.Future analysis will inspect changes in specific genes that may explain the role of the DG in reference memory and PS impairment.Cognitive impairment is associated with differential regulation of genes linked to defined neural systems. Age-related deficits in episodic memory are linked to altered transcriptional regulation in hippocampal subregion CA1, specifically in groups of genes related to Ca2+ homeostasis and synaptic plasticity. The dentate gyrus (DG) expresses more differentially expressed genes (DEGs) with age than other hippocampal subregions, but the significance of this dysregulation is unclear. The DG is implicated in the mnemonic process of pattern separation (PS), a computational process hypothesized to underlie the ability to encode similar experiences into distinct memories. This ability declines with age in humans and animal models. The DG is also known to undergo several changes with age, including a loss of synapses, slowing of neurogenesis, impaired synaptic plasticity, and shrinkage. Identification of transcriptomic changes that occur within hippocampal subregions of animals with age-related PS deficits may yield better understanding of the causes of these deficits and how they can be reversed. I hypothesize that middle-age animals with impaired PS ability express a distinct transcriptional profile of genes relevant to neural activity and neurogenesis relative to unimpaired animals, specifically within the DG, and that transcriptomic profiles of PS impairment will be distinct from those seen with reference memory impairment.IntroductionSummaryAcknowledgementsBehavior ResultsImpaired Pattern Separation During Aging is Associated with Altered Hippocampal Gene Transcription Garrett Smith,*1 Asha Rani,1 Ashok Kumar,1 Thomas C. Foster1,21Department of Neuroscience, McKnight Brain Institute, 2Genetics and Genomics Program, University of Florida, Gainesville, FL 32611Figure 2. Middle-age animals show deficits relative to young most distinctly when starting trials from points equidistant between the two beacons. Within middle-age animals, PS impairment correlated with reference memory (r = 0.72, p= 0.002). This may suggest an interaction between these cognitive abilities in middle age animals. Error bars = SEM.Transcription Results: Cognition RNA SequencingFigure 1. In the beacon discrimination task, animals began trials at one of six starting positions: two near the platform beacon (S+), two equidistant between the decoy and platform beacons, and two near the decoy beacon (S-). Spatial cues, platform and beacon positions were unchanged through all days of spatial testing. Figure 4. The DG of aged rats showed the greatest number of genes correlated with spatial PS performance. In the DG, a downregulation of synaptic and neurogenesis-related genes was seen with worse performance in spatial PS. CA1 and CA3 were less strongly implicated in spatial PS. Figure 6. Most genes correlating with spatial PS in the DG were also altered with age. Among genes both correlated with cognition and altered with age, worse performance was associated with an increases in genes regulating transcription regulation, and a decrease in synaptic genes. BenchComputational>>Filtered reads based on counts ≥5 average reads>>Alignment to rattus reference genome Annotation (Ensembl 92 rattus norvegicus)>>Normalization: DESEq2 (median of ratios)>>Statistical analysis: DESeq2 (p<0.025; Wald statistic) Correlations (r≥0.497) >>Functional clustering analysis DAVID; Cell Compartment, Biological Process, and Molecular Function, Benjamini FDR<0.05Transcriptional Dysregulation with AgeMiddle-age rats make more errors than young in the spatial PS taskMiddle-age rats show no impairment in reference memory compared to young ratsMiddle-age animals that perform well in reference memory tend to perform poorly in spatial PS Figure 3. Substantial gene dysregulation relative to young animals is notable by middle-age in all hippocampal subregions, particularly within the DG (DEG counts shown on right). Significant functionally related categories of genes related to age are shown for each subregion below. Across all subregions, age was associated with an upregulation of genes involved in gene expression, and a decline in genes relating to synaptic function and nervous system development. BP=Biologic Process, MF=Molecular Function, CC=Cell Compartment.Reference MemoryPattern SeparationFigure 5. In middle-age rats relative to young, the DG expressed the greatest number of genes and functional clusters of genes that correlated with reference memory performance. In contrast to trends seen with spatial PS, downregulation of synaptic genes in the DG was associated with better reference memory performance. MethodsTissue extractionRNA isolationPoly-A mRNA selectionLibrary constructionRNA sequencing on Ion Proton600.19/Y13BehaviorYoung (5 mo) and middle-age (12 mo) male F344 rats were characterized for spatial PS using a beacon task adapted from previous studies. Testing included cue training, spatial beacon discrimination (for PS), and spatial reference memory testing. Before sacrifice, rats were given 5 days of rest then tested on a 90° shifted beacon discrimination task.