Senescence-induced Spatio-temporal Re-organization of the Nuclear Lamina Dynamic Landscape at Single-molecule Level in Live Human RPE Cells

A defining hallmark of cellular senescence is the extensive remodeling of the nuclear lamina (NL) in both structure, composition, and its interactions with lamina-associated genomic domains. However, how such senescence-induced changes could quantitatively impact the spatio-temporal dynamics of NL interactions at the single-molecule level remain poorly understood. Herein, using human retinal pigment epithelium (RPE) cells as model system, we establish a robust, chemically inducible cellular senescence model capable of recapitulating key signatures of the senescence-associated phenotype. Senescent RPE cells exhibit distinct alteration patterns in the expression of various NL components, including lamin B receptor (LBR) and emerin, two key mediators of NL-chromatin interactions. Importantly, live-cell diffusion measurements via imaging FCS reveal globally enhanced mobility for both LBR and emerin, indicative of weakened NL anchoring in senescent cells. Single-molecule tracking and super-resolved STAR mapping further unveil distinct, multi-modal re-organization of their NL-binding dynamics in both space and time (especially in the form of LBR binding "hotspots" where multiple stable binding events cluster to effect more extended and prolonged interaction), in line with their respective expression-level alterations and differential lamin interactions. Moreover, correlative mapping uncovers a strong spatial coupling between reduced LBR mobility and highly condensed constitutive heterochromatin domains at the NL, which become dispersed during senescence. Collectively, these findings demonstrate the re-organization of NL dynamic landscape at single-molecule level as a critical and previously under-explored facet of senescence-induced NL remodeling, and point to a synergistic interplay between physical de-anchoring, dynamic attenuation of stable NL-binding and spatial restructuring of chromatin architecture in modulating NL-heterochromatin contacts to potentially effect global changes in senescence-associated gene expression.