ACSS2 drives senescence-associated secretory phenotype by limiting purine biosynthesis through PAICS acetylation

Senescence-associated secretory phenotype (SASP), an established feature of cellular senescence, mediates the biological effects of senescent cell on tissue microenvironment and contributes to aging-associated disease progression. The metabolic enzyme ACSS2 produces acetyl-CoA from acetate and epigenetically regulates gene expression through histone acetylation. Whether and how ACSS2 regulates cellular senescence through non-histone acetylation mechanisms remain unclear. Here we show that ACSS2 drives SASP by promoting PAlCS acetylation to restrain purine metabolism. Genetic and pharmacological inhibition, as well as deletion of Acss2 in mice blunts SASP gene expression and abrogates the pro-tumorigenic and immune surveillance functions of senescent cells. Mechanistically, ACSS2 directly interacts and promotes acetylation of PAlCS, a key enzyme for purine metabolism. The acetylation of PAlCS promotes autophagy-mediated degradation of PAlCS to limit purine metabolism and reduces dNTP pools for DNA repair, which exacerbates cytoplasmic chromatin fragment (CCF) accumulation and SASP. Altogether, our work links ACSS2-mediated local acetyl-CoA generation to purine metabolism through PAlCS acetylation that dictates the functionality of SASP, and identify ACSS2 as a potential senomorphic target for healthy aging and to prevent senescence-associated diseases. To investigate how ACSS2 regulates cellular senescence, we established oncogene-induced senescent IMR90 cells in which ACSS2 has been knocked down by shRNA. We then performed transcriptomic profiling using RNA-seq data of 3 groups of cells including proliferating, senescent cells with and without ACSS2 knockdown.

衰老相关分泌表型 (Senescence-associated secretory phenotype, SASP) 是细胞衰老的公认特征，可介导衰老细胞对组织微环境的生物学效应，并促进衰老相关疾病的进展。代谢酶ACSS2可利用乙酸盐合成乙酰辅酶A，并通过组蛋白乙酰化表观遗传调控基因表达。目前尚不清楚ACSS2是否以及如何通过非组蛋白乙酰化机制调控细胞衰老。本研究发现，ACSS2通过促进PAlCS的乙酰化以抑制嘌呤代谢，从而驱动SASP的产生。遗传与药理学抑制手段，以及在小鼠中敲除Acss2基因，均可削弱SASP基因的表达，并消除衰老细胞的促瘤及免疫监视功能。机制层面，ACSS2可直接与嘌呤代谢关键酶PAlCS结合，并促进其乙酰化；PAlCS的乙酰化可通过自噬介导其降解，进而限制嘌呤代谢，同时减少用于DNA修复的脱氧核糖核苷三磷酸 (deoxyribonucleoside triphosphate, dNTP) 池，最终加剧细胞质染色质片段 (cytoplasmic chromatin fragment, CCF) 的积累与SASP的产生。综上，本研究通过PAlCS乙酰化将ACSS2介导的局部乙酰辅酶A生成与嘌呤代谢关联起来，该通路可调控SASP的功能，并将ACSS2鉴定为健康衰老及预防衰老相关疾病的潜在衰老修饰靶点。为探究ACSS2如何调控细胞衰老，我们构建了经短发夹RNA (short hairpin RNA, shRNA) 敲低ACSS2的癌基因诱导衰老IMR90细胞模型，随后对三组细胞（增殖组、衰老组、衰老且ACSS2敲低组）进行RNA测序转录组分析。