Extranuclear DNA accumulates in aged cells and contributes to senescence and inflammation.

Yuk Yuen Lan,Nir Hacohen,James M Heather,Thomas Eisenhaure,Christopher Stuart Garris,Raktima Raychowdhury,David Lieb

doi:10.1111/acel.12901

Abstract

Systemic inflammation is central to aging‐related conditions. However, the intrinsic factors that induce inflammation are not well understood. We previously identified a cell‐autonomous pathway through which damaged nuclear DNA is trafficked to the cytosol where it activates innate cytosolic DNA sensors that trigger inflammation. These results led us to hypothesize that DNA released after cumulative damage contributes to persistent inflammation in aging cells through a similar mechanism. Consistent with this notion, we found that older cells harbored higher levels of extranuclear DNA compared to younger cells. Extranuclear DNA was exported by a leptomycin B‐sensitive process, degraded through the autophagosome–lysosomal pathway and triggered innate immune responses through the DNA‐sensing cGAS‐STING pathway. Patient cells from the aging diseases ataxia and progeria also displayed extranuclear DNA accumulation, increased pIRF3 and pTBK1, and STING‐dependent p16 expression. Removing extranuclear DNA in old cells using DNASE2A reduced innate immune responses and senescence‐associated (SA) β‐gal enzyme activity. Cells and tissues of Dnase2a− / − mice with defective DNA degradation exhibited slower growth, higher activity of β‐gal, or increased expression of HP‐1β and p16 proteins, while Dnase2a− / −;Sting− / − cells and tissues were rescued from these phenotypes, supporting a role for extranuclear DNA in senescence. We hypothesize a direct role for excess DNA in aging‐related inflammation and in replicative senescence, and propose DNA degradation as a therapeutic approach to remove intrinsic DNA and revert inflammation associated with aging.

Highlights

Aging is associated with increased risk of heart disease, cancer, diabetes, cognitive decline, and many other pathological conditions.While numerous mechanisms are likely to be relevant, systemic changes in the inflammatory response with aging are likely to impact the risk of these diverse conditions
Consistent with our original model of extranuclear DNA being processed by autophagy and stimulating the STING pathway, we found that olds cells treated with bafilomycin A1 showed increased levels of MX1 and CXCL10, while cells treated with rapamycin reduced MX1 expression (Figure 2f)
We focused on two genetic disorders, ataxia telangiectasia (AT), a severe neurodegenerative syndrome caused by gene defects in ATM which is essential for double‐stranded breaks (DSBs) repair, and Hutchinson–Gilford progeria (HGPS or PS), which exhibits premature aging symptoms due to a mutation in LAMIN A (LMNA) that maintains nuclear architecture

Summary

| INTRODUCTION

Aging is associated with increased risk of heart disease, cancer, diabetes, cognitive decline, and many other pathological conditions. Heightened inflammation is observed in aging tissues, and in the blood of older adults in large epidemiologic studies, with consistently higher basal levels of C‐reactive protein and abundant pro‐ inflammatory cytokines like IL‐6, IFN‐β, and TNF‐α (Fagiolo et al, 1993; Roubenoff et al, 2003; Singh & Newman, 2011) Such alteration is often viewed as noncell autonomous, for example senescent cells, which increase with aging, may modulate inflammation through secretion of cytokines (i.e., senescence‐associated secretory phenotype, SASP (Coppé et al, 2010)). We test our original model in the context of aging, observing how nuclear DNA connects the intrinsic processes of damage, autophagy, sensing, degradation, and the induction of innate immune responses.

| RESULTS

| DISCUSSION

| EXPERIMENTAL PROCEDURES

Findings

CONFLICT OF INTEREST