端粒结合蛋白TRF2通过调控端粒脱帽参与血管内皮细胞衰老的机制研究

The integrity of telomere t-loop is fundamental for maintaining the homeostasis of chromosome. As a key component of Shelterin family, the TTAGGG repeat binding factor-2 (TRF2) protects telomeres and maintain the t-loop. Breakdown of the t-loop structure, or telomere uncapping, caused by critically genotoxic stressors will induce a sustained double-stranded DNA breaks (DSBs), which contributes to the senescence-associate phenotype change. Recent evidence and our previous work have indicated that telomere uncapping induced by dysfunction of TRF2 per se, independent of telomere shortening, function as the key mechanism for p53-mediated senescence-associated arterial dysfunction. However, due to lacking of ideal animal models, the precise role of TRF2 in endothelial cell senescence is still poorly understood. In the present study, we aim to further evaluate the TRF2/telomere uncapping on endothelial cell senescence based on a conditional knock-out mice strain Trf2 f/f-VE-Cadherin-Cre+. After 5 days treatment of tamoxifen, we plan to perform the aging-related vascular function test to evaluate the physiological role of TRF2. In addition, we isolate and culture the primary mouse pulmonary artery endothelial cells to further explore the mechanism and downstream signaling of TRF2. Based on replicative senescence and stress-induced senescence model, we employ lentivirus transfection system to induce overexpression/silence TRF2 in primary HUVEC, which will provide direct evidence to show which domain of TRF2 is responsible for the telomere uncapping-dependent phenotype during endothelial cell senescence. We believe that our study would identify novel pharmaceutical targets for the prevention/treatment of age-related arterial dysfunction, which is a significant goal given the increasing number of older adults and their high risk for CVD and the associated health care burden.

端粒帽结构是染色体稳态的重要调控机制，TRF2作为维系帽结构的核心因子，其功能异常将诱导端粒脱帽，并与衰老相关DNA损伤应答密切相关。我们前期的研究以及最新文献均表明在血管生理性衰老中，TRF2失活所诱导的端粒脱帽可能是独立于端粒缩短的重要调控机制。然而，由于缺乏理想的动物模型，国内外对于TRF2在内皮细胞衰老中的研究仍处于起步阶段。本项目将运用内皮细胞条件性敲除小鼠Trf2fl/fl-VE-Cadherin-Cre+，系统观察评估TRF2对衰老相关血管功能的影响；通过分离培养原代小鼠内皮细胞，离体水平验证TRF2在内皮细胞衰老中的作用；基于多种体外衰老模型，通过慢病毒转染技术敲除/敲入野生型及突变型TRF2，阐明内皮衰老过程中TRF2及端粒脱帽的具体作用机制和关键结构域，探索以TRF2为靶点稳定端粒帽结构的作为抗血管衰老策略的潜在价值，为未来临床上预防和延缓血管衰老提供新的突破口。

端粒帽结构是染色体稳态的重要调控机制，TRF2作为维系帽结构的核心因子，其功能异常将诱导端粒脱帽，并与衰老相关DNA损伤应答密切相关。在血管生理性衰老中，TRF2失活所诱导的端粒脱帽可能是独立于端粒缩短的重要调控机制。然而，由于缺乏理想的动物模型，国内外对于TRF2在内皮细胞衰老中的研究仍处于起步阶段。本研究从以下3个方面展开：1) 评估内皮细胞条件性敲除Trf2小鼠模型的衰老相关血管功能；2）探索原代小鼠内皮细胞沉默Trf2基因对表型及功能的影响；3）利用慢病毒转染技术，建立过表达及沉默TRF2的原代内皮细胞，以此为模型探索TRF2调控内皮细胞衰老的核心分子机制。课题基本按照研究计划进行。首先顺利完成了转基因模式动物的培育与鉴定，多批次摸索Cre-LoxP的激活条件，最终确定有效诱导条件。初步探索了条件性诱导内皮细胞TRF2基因敲除可导致血管内皮舒张功能障碍，血管硬度增加等血管衰老相关表型，伴随运动耐力减低；通过延长培育周期，进一步证实内皮细胞敲除TRF2可以累积DNA损伤，导致血管内皮舒张功能进一步下降。通过分别提取年轻及自然衰老小鼠的原代内皮及平滑肌细胞进行功能学检测，提示血管退行性病变的主要原因之一可能是内皮细胞功能受损相关。随增龄内皮细胞明显受损，并伴随着端粒脱帽现象；而平滑肌细胞随增龄其表型或端粒帽结构未发生明显变化。通过离体培养Trf2f/f-VE-Cadherin-Cre+小鼠的原代内皮细胞，体外诱导Cre-LoxP系统激活，证实内皮细胞特异性诱导TRF2敲除可导致增殖及迁移能力降低，伴随着衰老细胞比例的增高。通过以上实验，我们证实TRF2所调控的端粒帽结构是维系衰老相关内皮功能稳态的核心因子之一，TRF2表达降低所诱导的端粒脱帽可能是血管内皮细胞衰老的重要机制之一，明确端粒脱帽机制在血管内皮细胞衰老中的作用和地位。