调节NF-kappaB在衰老进程中转录激活功能的表观遗传学机制研究

Aging and cellular senescence are featured by arrays of distinctive phenotypes and biomarkers. Among them, there was a burst of investigations on secretory factors associated with inflammation and malignancy, which were designed as "senescence-associated secretory phenotype" (SASP) owing to their induction by replicative or stress-triggered senescence. These myriad factors, including IGFBPs, PAI1, TGF-beta, WNT, and panels of cytokines, chemokines and interferons, contribute to aging process in an autocrine, paracrine and even endocrine fashion via their collaborations with DNA damage response. Manipulations of SASP and DNA damage coordinately accelerate and reinforce development of aging through activation of p53- and p16- centered tumor suppressor networks. Nuclear factor-kappaB (NF-kappaB) is the master regulators responsible for transcriptional activation of inflammation machinery, and subunit of this family was identified as major transcription factor accumulated on chromatin of senescent cells. Further evidence suggested the causal relationship between NF-kappaB activity and SASP during senescence. The nuclear activity of NF-kappaB is shaped by various histone modifications and ATP dependent remodeling complexes beyond its affinity toward cis- DNA elements. These combinational epigenetic strategies could be devised to control selective activation of pro-inflammatory gene transcription and maintain response to stresses along with aging taking place. However, in comparison to well-established epigenetic mechanisms for NF-kappaB activation in immune system, specific histone modifications and chromatin structure favoring NF-kappaB action in senescence remains elusive. In our pilot experiments, a group of active histone modification marks and accompanying BCL3/Tip60 complex were found to be tightly associated with specialized subsets of secreting factors which could be induced in a NF-kappaB dependent manner during SASP. Ablation of WDR5 (a critical component to establish active histone modification) severely impaired the recruitment of BCL3/Tip60 complex and resulted in alleviation of secretory phenotype in senescence. In order to expanded this observation and explore more underlying epigenetic infrastructures, we intend to equip genomic high throughout technique and conventional biochemical and molecular biological methodologies to systemically evaluate combinational histone code and chromatin structures impacting the transcriptional outcome of NF-kappaB during senescence. We believe the elucidation of mechanistic details for epigenetic regulation on NF-kappaB-cis-DNA-elements transactions would not only contribute to the molecular dissection of aging, but also provide novel pharmatheutical target with the aim of ameliorating functional decline caused by SASP.

衰老相关的分泌表型(senescence-associated secretory phenotype, SASP)是新近发现的一种机体在衰老时所呈现出的分子特征。参与SASP的分子包括干扰素、白介素等致炎因子，而 NF-kappaB作为调控诸多炎性分泌蛋白基因表达的转录因子，在SASP的发生和发展过程中起着重要作用。目前，影响NF-kappaB活性的衰老相关机体环境究竟如何尚属未知。我们的前期工作中发现特定组蛋白修饰和染色质构象决定了衰老过程中NF-kappaB调节下游基因激活的选择性和特异性。我们相信进一步在基因组水平上验证并拓展该结论，将有助于我们理清SASP发生的分子机制，阐明影响衰老发生的表观遗传学特征及其生理意义。此外我们还将对组蛋白修饰的特定抑制剂进行筛选，以期寻找到可以通过抑制NF-kappaB介导的SASP延缓细胞衰老的药物靶点，为临床相关的衰老疾病治疗提供新思路。

此项目的经费用于衰老和肿瘤发生的表观遗传学机制研究。在研期间共发表论文三篇，总影响因子约35分。其中影响因子最高的论文发表在Nature Genetics上（IF:31.6），这篇论文聚焦于调控细胞状态的表观遗传学机制，展示了转录因子在表观遗传重编程和细胞功能可塑性中的新颖机制。剩余两篇论文或阐明了衰老相关转录因子和衰老关键蛋白p16的表达变化在肿瘤发生中的作用；或者探索了组蛋白修饰酶在基因转录调控中的作用方式。在本课题执行过程中，我们筛选出一些新颖的组蛋白修饰结合蛋白。它们中间有一些参与衰老相关分泌表型的调控，与衰老发生密切相关。这些组蛋白修饰可以调节细胞衰老过程中NF-kappaB激活的组织特异性和基因特异性；它们通过与环境应激相互作用，改变细胞衰老的微环境，影响细胞周期进展和其正常的生理功能。这些发现为我们下一步工作打下了良好的基础。