Senescence-specific translation dysregulation desensitizes cells to stress by inhibiting activation of the integrated stress response

Senescence is a state of indefinite cell cycle arrest associated with aging, cancer, and age-related diseases. Here we find that translational deregulation and a corresponding maladaptive integrated stress response (ISR) is a hallmark of senescence that desensitizes senescent cells to stress. We present evidence that senescent cells maintain high levels of eIF2? phosphorylation, typical of ISR activation, but translationally repress production of the stress response transcription factor 4 (ATF4) by ineffective bypass of the inhibitory upstream open reading frames (uORFs). Surprisingly, ATF4 translation remains inhibited even after acute proteotoxic and amino acid starvation stressors, resulting in a highly diminished stress response. We also find that stress augments the senescence associated secretory phenotype with sustained remodeling of inflammatory factors expression that is suppressed by non-uORF carrying ATF4 mRNA expression. Our results thus show that senescent cells possess a unique response to stress that entails an increase in their inflammatory profile. Overall design: Ribosome sequencing analysis of cycling, senescent, quiescent, and Tg-stressed IMR90 fibroblasts. RNA and Ribo-seq material harvested in parallel. Ribo-seq footprints generated by incubating RNA with RNAse I at 4C for 20 minutes.

细胞衰老是一种与衰老、癌症及年龄相关疾病相关的不可逆细胞周期阻滞状态。本研究发现，翻译调控紊乱以及与之对应的适应不良型整合应激反应（integrated stress response, ISR）是衰老细胞的标志性特征，该特征可使衰老细胞对应激产生脱敏。我们的研究证据表明，衰老细胞维持高水平的eIF2?磷酸化——这是ISR激活的典型特征，但通过无效绕过抑制性上游开放阅读框（upstream open reading frames, uORFs）的方式，在翻译层面抑制了应激响应转录因子4（ATF4）的产生。令人意外的是，即便在急性蛋白毒性应激与氨基酸饥饿应激刺激后，ATF4的翻译仍处于抑制状态，这导致应激响应能力大幅减弱。我们还发现，应激会加剧衰老相关分泌表型，伴随炎症因子表达的持续性重塑，而该重塑可通过表达不含uORFs的ATF4 mRNA得以抑制。综上，我们的研究结果显示，衰老细胞拥有独特的应激响应机制，该机制会使其炎症特征增强。实验整体设计：对增殖期、衰老期、静息期以及经Tg应激处理的IMR90成纤维细胞开展核糖体测序分析。同步收集RNA与Ribo-seq样本。Ribo-seq足迹通过将RNA与RNA酶I在4℃下孵育20分钟生成。