High-resolution Hi-C reveals increased chromatin looping with senescence associated with hypomethylation and retrotransposon derepression [Hi-C]

This study presents the highest-resolution chromatin map of cellular senescence to date, shedding light on how genomic architecture is altered with this damaging phenotype. Senescence, a driver of aging, is a pro-inflammatory state of proliferative arrest caused by DNA damage; it is associated with epigenetic changes, including those to chromatin organization. We created ~3kb Hi-C contact maps of proliferating, quiescent, and replicative senescent lung fibroblasts, and also compared these to oncogene-induced senescence. Our findings confirm a loss of heterochromatin, with a shift towards the A compartment and A subcompartments. We establish a novel loop analysis framework, revealing the ~six times more unique loops with senescence, which lose methylation at their anchors. Additionally, we present a custom long-read reference genome highlighting structural changes supporting retrotransposon derepression, particularly at a defined 'hotspot'. These architectural changes contribute to senescence, as they promote cell cycle arrest and inflammation, as well as epigenetic drift. Overall design: To investigate the role of genomic structure in cellular senescence we generated Hi-C data, total RNA-seq, and long-read DNA sequencing for proliferating and late replicative senescent human diploid lung fibroblasts (LF1). We also generated Hi-C and total RNA-seq for quiescent cells. We compared the proliferating, quiescent, and senescent cell data to determine characteristic architectural features of senescence.