研究细胞/组织器官衰老与机体衰老关联机制的条件性敲入小鼠模型的建立与分析

Aging is a lifetime-long progressive decline of physiological functions, characterized with cellular senescence and reduced tissue regeneration capacity. Understanding the mechanisms of aging will help to lessen the impact of aging population via developing interventions to prevent the development or slow down the progression of age-related diseases, like cardiovascular diseases, type 2 diabetes mellitus and cancer etc. However aging process is rather complicated and many fundamental questions are still poorly understood, like what is the contributing role of cellular senescence during organism aging? Which tissues/organs are critical for organism aging?..Hutchinson-Gilford progeria syndrome (HGPS) caused by a Lamin A mutant, i.e. Progerin, is a rare premature ageing genetic disorder. Patients suffering from HGPS have a mean age of 13.4 years and are clinically characterized with early growth retardation, short stature, lipodystrophy, alopecia, stiff joints, osteoporosis, dilated cardiomyopathy and atherosclerosis. Mouse models harboring the same mutation recapitulates many progeroid features of HGPS. Moreover, low level of progerin is also expressed in normal human cells. The level and the number of positive cells increase along with age-related telomere attrition. Given its close resemblance to normal aging, HGPS is extensively studied during the last decade as an ideal model to understand human aging. Previously, we have found that progeria cells undergo early senescence owing to delayed chromatin remodeling and defective DNA repair (Nature Medicine 2005, PNAS 2011, Nature Communications 2013 and Aging Cell 2013). We found that resveratrol, a small molecule mimic of caloric restriction, enhances mesenchymal stem cell self-renewal, ameliorates premature aging features and extends lifespan in a progeria mouse model (Cell Metabolism 2012). However, studies based on conventional knock-out or knock-in mouse models are difficult to answer basic questions like the causal links between cellular/tissue aging and organism aging. Here we propose to generate a progerin conditional knock-in (Pro-CKI) mouse model. Together with tissue specific Cre transgenic mice, Pro-CKI mice can be used to investigate tissues or organs that are critical for organism aging, and the causal role of cellular senescence in organism aging. In this project, we will take vascular smooth muscle and mesenchymal stem cell aging as examples to investigate their contributions to accelerated aging.

细胞衰老是机体衰老的原因还是结果？哪些组织器官衰老加速机体老化？这些衰老研究的重大科学问题亟待解决。Lamin A突变（Progerin）加速人体老化，导致HGPS早老症，为衰老研究提供了极具特色的疾病模型。我们过往以全身性基因敲除早衰小鼠为模型，从基因组不稳定性、表观遗传、染色质重塑、干细胞衰老等角度对早老症的致病机制与治疗策略进行了广泛研究。然而，现有全身性敲除模型难以回答“细胞衰老和组织器官退化是机体衰老的因还是果”这一“鸡先还是蛋先”的科学难题。本项目拟构建条件性敲入Progerin（Pro-CKI）小鼠，若借助组织特异的Cre小鼠，可用于研究特定组织器官衰老的分子机制与生理特性，揭示组织器官衰老与机体老化之间的互作机制，验证细胞衰老加速机体衰老这一重大科学假说。我们将举例探讨血管平滑肌或干细胞衰老与机体衰老的关联机制及干细胞抗衰老治疗的可行性。

衰老是老年慢病的最大危险因子；理解衰老机制，是从根本上实现老年慢病的早期预警与治疗，实现健康老龄化的关键所在。本项目旨在构建一个可用于研究组织器官衰老与机体衰老之间关联机制的条件性敲入早衰小鼠模型。项目成功构建了LmnaG609G条件性敲入小鼠模型（Lmnaflox/flox），借助EIIA-Cre工具鼠，获得了全身性敲入小鼠模型（LmnaG609G/G609G），整体表现为系统性衰老。利用血管内皮特异工具鼠—Tie2-Cre，获得了血管内皮特异衰老/功能紊乱的小鼠模型，进一步研究发现：血管内皮功能紊乱足以加速整体衰老。原因是Lamin A异常导致SIRT7蛋白稳定性下降引发系统性的炎症反应。靶向血管内皮、AAV介导的SIRT7基因治疗可显著延长寿命（加倍）（Science Advances，接收发表）。此外，本项目也构建了SIRT7全敲除和条件性敲除模型，利用此模型发现了中央生物节律钟通过光-体温-HSP70-SIRT7-CRY1轴同步化肝脏生物节律钟的分子机制（Nature Metabolism 2019）。本项目的研究成果发现血管内皮衰老显著加速系统衰老，阐释了SIRT7调控血管内皮衰老与肝脏生物节律和糖代谢的机制，对于早期预防与临床治疗老年相关疾病具有重要的理论指导意义。