Locus-specific induction of gene expression from heterochromatin loci during cellular senescence

Abstract

Abstract Cellular senescence is a fate-determined state, accompanied by reorganization of heterochromatin. While lineage-appropriate genes can be temporarily repressed through facultative heterochromatin, stable silencing of lineage-inappropriate genes often involves the constitutive heterochromatic mark, histone H3K9me3. The fate of these heterochromatic genes during the chromatin reorganization accompanying senescence is unclear. Here we show a small number of lineage-inappropriate genes are derepressed in senescent cells from H3K9me3 regions that gain open chromatin marks. DNA FISH experiments reveal that these gene loci, which are tightly condensed at the nuclear periphery in proliferative cells, are physically decompacted during senescence. Among these gene loci, NLRP3 is predominantly expressed in immune cells, such as macrophages, where it resides within an open topologically associated domain (TAD). In contrast, NLRP3 is derepressed in senescent fibroblasts, potentially due to the local disruption of the H3K9me3-rich TAD that contains it. The role of NLRP3 has been implicated in the amplification of inflammatory cytokine signalling in senescence and aging, underscoring the functional relevance of gene induction from ‘permissive’ H3K9me3 regions in senescent cells.