Nuclear expansion and chromatin structure remodeling in mouse aging neurons.

Aging, particularly in the brain, involves impairments in multiple cellular functions, many regulated at the nucleus. Chromatin structure plays a critical role in regulating gene expression and the maintenance of genomic stability. During differentiation, each cell type acquire their unique topology, this should be kept for a lifetime, but may deteriorate as we age. However, the effects of aging on the chromatin 3D structure of neurons remain largely unknown and much has been inferred from senescent cells. By combining chromosome conformation capture and microscopy techniques, we investigated cortical neurons of young and aged mice and discovered signs of neuronal nuclear expansion during neuronal aging, leading to increased distances between chromosomes. This expansion alters the topology of compartments, topologically associating domains (TADs) and chromatin loops. While larger TADs tend to dissociate, smaller TADs and loops exhibit strengthened interactions of chromatin in aged neurons. These topological changes impact the borders of TADs, resulting in weakening, this is parallel to Lamin-B weakening and nuclear envelope alterations. We attribute these alterations to changes in physical forces of an expanding nucleus, driving the distancing of chromosomes filling a growing nuclear area, affecting gene expression and topology, contributing to the functional declines observed during aging.