# Senescent cells secrete chromatin components via senescence-associated extracellular particles

## TL;DR

Senescent cells release chromatin fragments through unique particles, which may trigger inflammation in other cells.

## Contribution

Discovery of a novel extracellular signaling mechanism by senescent cells involving chromatin components.

## Key findings

- Senescent cells secrete γH2AX and dsDNA via popcorn-like extracellular particles.
- Autophagy inhibition increases secretion of chromatin components.
- CCF-containing particles activate cGAS-STING signaling in non-senescent cells.

## Abstract

Senescent cells influence their surroundings through the senescence-associated secretory phenotype (SASP), an assortment of secreted molecules and macromolecular complexes. Among SASP’s intracellular drivers are cytoplasmic chromatin fragments (CCFs), nuclear-derived DNA that activates the pro-inflammatory cGAS/STING pathway. While autophagy contributes to CCFs degradation, the full repertoire of CCF fates and signaling functions remains unclear. Here, we show that senescent cells release CCF components, γH2AX and double-stranded DNA (dsDNA), into the extracellular space via an ESCRT-independent multivesicular body pathway. Secreted CCF components localize to extracellular particles exhibiting an unusual “popcorn”-like morphology, distinct from canonical small extracellular vesicles. Notably, inhibition of autophagy enhances secretion of CCF components and particles, suggesting an inverse relationship between intracellular clearance and extracellular release. A fraction of CCF-containing extracellular particles activates cGAS-STING signaling in non-senescent proliferating cells and is enriched in the circulation of aged mice, pointing to a previously unrecognized mode of extracellular signaling by senescent cells.