SIRT1 Suppresses the Senescence-Associated Secretory Phenotype through Epigenetic Gene Regulation

Tomohisa Hayakawa,Noboru Motoyama,Wakako Maruyama,Mitsuo Maruyama,Mika Iwai,Koichi Takimoto,Satoshi Aoki,Alexander James Roy Bishop

doi:10.1371/journal.pone.0116480

Abstract

Senescent cells develop a pro-inflammatory response termed the senescence-associated secretory phenotype (SASP). As many SASP components affect surrounding cells and alter their microenvironment, SASP may be a key phenomenon in linking cellular senesence with individual aging and age-related diseases. We herein demonstrated that the expression of Sirtuin1 (SIRT1) was decreased and the expression of SASP components was reciprocally increased during cellular senescence. The mRNAs and proteins of SASP components, such as IL-6 and IL-8, quickly accumulated in SIRT1-depleted cells, and the levels of these factors were also higher than those in control cells, indicating that SIRT1 negatively regulated the expression of SASP factors at the transcriptional level. SIRT1 bound to the promoter regions of IL-8 and IL-6, but dissociated from them during cellular senescence. The acetylation of Histone H3 (K9) and H4 (K16) of the IL-8 and IL-6 promoter regions gradually increased during cellular senescence. In SIRT1-depleted cells, the acetylation levels of these regions were already higher than those in control cells in the pre-senescent stage. Moreover, these acetylation levels in SIRT1-depleted cells were significantly higher than those in control cells during cellular senescence. These results suggest that SIRT1 repressed the expression of SASP factors through the deacetylation of histones in their promoter regions.

Highlights

Cellular senescence is a state of irreversible cell cycle arrest that is caused by various cellular stresses, such as telomere shortening, oxidative stress, DNA damage, and the aberrant activation of oncogenes [1,2]
IL-8 mRNA, one of the senescence-associated secretory phenotype (SASP) components, was highly induced in senescent MRC-5 cells that had exposed to x-radiation.Consistent with previous reports [12,36,37,38,39], the human telomerase reverse transcriptase (hTERT)-mediated immortalized MRC-5 (MRC-5/TERT) and BJ (BJ/TERT) cell lines underwent senescence and the induction of IL-8 mRNA was observed upon x-radiation (Fig. 1A)
Expression of the SIRT1 protein was decreased 3 days after the induction of senescence (Fig. 1B). These results indicated that the reduction in the SIRT1 protein preceded the induction of SASP components, regardless of the expression of hTERT

Summary

Introduction

Cellular senescence is a state of irreversible cell cycle arrest that is caused by various cellular stresses, such as telomere shortening, oxidative stress, DNA damage, and the aberrant activation of oncogenes [1,2]. SIRT1 has been shown to repress gene expression by silencing the chromatin structure through its histone deacetylation activity [32]. SIRT1 bound to the promoter regions of SASP components, but dissociated from these regions in response to DNA damage, a key senescence stimulus. The depletion of SIRT1, but not its overexpression, enhanced the acetylation levels of histone H3 and H4 on the promoter regions of SASP components even in cells at the pre-senescence stage and those undergoing senescence. These results demonstrated that SIRT1 regulated the expression of SASP components through epigenetic gene regulation

Materials and Methods

Results

Discussion