The metabolic-epigenetic axis in memory

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Abstract Understanding the molecular machinery underlying learning is critical to improve therapies for memory-related disorders that continue to burden our society. We recently identified a connection between cellular metabolism, epigenetic regulation, and memory-related neuronal plasticity. We found that ACSS2, a metabolic enzyme that generates acetyl-CoA is chromatin-bound in hippocampal neurons and required for long-term spatial memory, a cognitive process that relies on histone acetylation and gene expression. While these results established a strong functional link between nuclear acetyl-CoA generation by ACSS2, histone acetylation, transcription and memory, the exact molecular underpinnings of this metabolic- epigenetic axis remain to be elucidated. Here we propose to explore this phenomenon in further mechanistic detail. In particular, we aim to identify ACSS2-associated proteins, examine the mechanism of ACSS2 recruitment to specific genes, and identify higher-order structures that contribute to ACSS2-mediated transcriptional regulation via chromatin looping. Moreover, we will explore dorsal hippocampal transcriptional and epigenetic changes that accompany memory formation in a hippocampus-dependent mammalian learning model (spatial object recognition). We will assess genome-wide changes in transcript abundance and chromatin accessibility, study the enrichment of histone post-translational modifications, and the re-distribution of ACSS2 and select histone acetyl marks. Finally, using an array of pharmacological and genetic tools, we will assess the contribution of ACSS2 to the observed transcriptional, epigenetic and behavioral phenotypes. In addition, our preliminary data under Aim 3 indicate that ethanol-derived acetyl-groups are rapidly incorporated into neuronal chromatin in an ACSS2-dependent manner. This remarkably rapid epigenetic response might underlie alcohol-induced transcriptional and behavioral maladaptations in heavy drinkers. Indeed, we found that treating primary hippocampal neurons with acetate (the alcohol-derived metabolite and direct substrate of ACSS2) upregulates learning and memory-related genes and that ACSS2 reduction eliminates alcohol-related associative learning in conditioned place preference. We will explore hippocampal transcriptional and epigenetic changes associated with alcohol exposure in mice in vivo and assess the contribution of ACSS2 to molecular and cellular alterations induced by alcohol. Further, we will assess the effect of small molecule ACSS2 inhibitors on alcohol-related behaviors, as a basis for future therapeutic interventions. Overall, this work will significantly advance the field by characterizing the metabolic-epigenetic axis in the context of learning neurobiology. Furthermore, we expect our studies to identify efficacious novel therapeutic avenues for memory impairments and associated neurological and psychiatric conditions.