Whole-genome profiling of native 5-hydroxymethylation in human neurons with long-read sequencing

The 5-hydroxymethylcytosine (5hmC) modification of DNA is particularly prevalent in neurons and thereby a hallmark of the brains epigenetic landscape. While 5mC DNA methylation is a well-known player in genome stability and transcriptional regulation, the role of 5hmC remains largely unknown. Here, we used long-read Oxford Nanopore Technology (ONT) to profile whole-genome, native 5mC and 5hmC levels in sorted neuronal nuclei samples from human post-mortem brain tissue. We applied different models for DNA modification calling and compared with array-based 5mC and 5hmC levels derived from the same samples, demonstrating high sample-wise correlations. Annotation across genomic and regulatory features, as well as chromatin states, generated by the International Human Epigenome Consortium, revealed high levels of 5hmC in introns, actively transcribed genes and (distal) enhancers. Pathway analysis of genes with high levels of 5hmC (> 60%) were enriched in neuron-related terms, with functional variety when stratifying across chromatin states. Analysis of transcription factor motifs in highly methylated regions, demonstrated 5hmC- and 5mC-specific enrichment affecting downstream regulatory networks. Altogether, our study demonstrates the potential of ONT to characterize whole-genome, native 5hmC and 5mC DNA modifications in human neurons, specifically highlighting the enrichment of 5hmC in actively transcribed regions and enhancers in the human brain.