DYSREGULATION OF THE m6A EPITRANSCRIPTOME AS A NEW MECHANISM INVOLVED IN HIPPOCAMPAL-DEPENDENT MEMORY DEFECTS IN HD MICE

Recent advances in RNA biology have focused on a new layer of gene expression regulation termed Epitranscriptomics. One of the most common mRNA modifications that is highly abundant in brain is N6-methyladenosine (m6A), which has been involved in learning and memory processes. Indeed, different studies have shown that m6A levels vary in response to cognitive tasks. This mark is dynamically regulated by a multicomplex of methyltransferases (METTL3, METTL14 and WTAP) as well as a series of demethylases (FTO and ALKBH5). Given the early cognitive symptomatology in Huntington’s Disease (HD), we aimed to determine whether expression of mutant huntingtin (mHtt) induces changes in the m6A epitranscriptome profile and signaling, leading to the memory and learning deficits observed in HD. For this purpose, genetically modified HdhQ7/Q111 mice were subjected to a hippocampal training task and relative levels of the m6A-modifying proteins were determined in different cellular compartments. In addition, identity of mRNAs with altered m6A profiles was determined through methylated RNA immunoprecipitation sequencing (meRIP-seq). Our results have shown that symptomatic HD mice display altered levels of FTO and METTL14, both in the nuclear as well as in the synaptic compartment. Moreover, transcriptome-wide profiling of m6A-modifed mRNAs has revealed a more prominent decrease in methylated peaks in HD mice in response to a training task when compared to age-matched wild type (WT) littermates. Interestingly, genes that show differential m6A peaks include immediate early genes and genes involved in synapse and neuronal function, among others. Thus, our results suggest that the altered levels of the m6A-modifying machinery in HD mice could be leading to a differential epitranscriptomic profile, contributing to the cognitive symptomatology observed in those animals. Altogether, our data uncover a promising role of m6A as a novel hallmark of the disease, pointing to this RNA chemical modification as a potential target to improve cognitive disturbances among HD patients Input and m6A immunoprecipitated RNA from three biological replicates were analyzed for each of 8 conditions (two genotypes; two ages, two treatments per genotype per age). Genotypes:HdhQ7/7 (wild-type) and HdhQ7/Q111 (KI) . Ages: 5 and 8 months. Conditions: Naive (non-trained) and trained Differential binding analysis: Metadata_v8_edited_8.10.bed.gz (KI_c8 vs KI_tr8 (all the replicates merged)) Metadata_v8_edited_8.1.bed.gz (KI_c5 vs WT_c5 (all the replicates merged)) Metadata_v8_edited_8.2.bed.gz (KI_c8 vs WT_c8 (all the replicates merged)) Metadata_v8_edited_8.3.bed.gz (KI_tr5 vs WT_tr5 (all the replicates merged)) Metadata_v8_edited_8.4.bed.gz (KI_tr8 vs WT_tr8 (all the replicates merged)) Metadata_v8_edited_8.5.bed.gz (WT_c5 vs WT_tr5 (all the replicates merged)) Metadata_v8_edited_8.6.bed.gz (KI_c5 vs KI_tr5 (all the replicates merged)) Metadata_v8_edited_8.7.bed.gz (c5 vs tr5 (all the replicates merged)) Metadata_v8_edited_8.8.bed.gz (c8 vs tr8 (all the replicates merged)) Metadata_v8_edited_8.9.bed.gz (WT_c8 vs WT_tr8 (all the replicates merged))