Autophagy-mediated chromatin degeneration in aging and age-related diseases

人类衰老和许多与年龄相关的疾病都与蛋白质稳态改变有关， 或者蛋白质代谢。蛋白平衡的关键调节因子之一是自噬，这是一种进化上保守的 通过溶酶体降解多种细胞成分的膜运输过程。自噬 是在饥饿和卡路里限制期间诱导的，对维持细胞和组织的完整性是必不可少的。 虽然自噬降解细胞质是众所周知的，但最近我做了一个令人惊讶的 发现哺乳动物的自噬能够降解核成分(Dou等人，《自然》，2015)。这个 自噬蛋白Lc3存在于细胞核中，并直接与核层蛋白Lamin B1相互作用， 并在全基因组水平上与染色质上的层蛋白相关结构域(LADS)相关联。这种互动 调节Lamin B1和相关异染色质的运输和降解，通过一个核到- 细胞质运输过程，导致它们在细胞质溶酶体中被消化。这个薄层和染色质 自动消化专门发生在细胞衰老期间，这是细胞周期停滞的一种稳定形式。衰老是一种 响应癌基因激活的特化细胞状态，有利于抑制肿瘤的发生； 然而，衰老也是在衰老过程中诱导的，这导致了与年龄相关的病理。我发现 抑制自噬或Lc3-Lamin B1相互作用可阻止Lamin B1的降解并延长 手机寿命。这些发现首次证明了哺乳动物的自噬具有功能性。 在维持细胞核内稳态方面的作用，为理解哺乳动物的衰老提供了一个新的方向， 并引发了许多需要解决的问题。 在这项提案中，我计划调查核自噬的这一新视角，并研究其影响 染色质与衰老的关系。我的中心假设是，尽管染色质的自噬退化是一种 内在的肿瘤抑制机制，矛盾的是，它在衰老过程中不适当地适应，并有助于 与年龄相关的病理。我还假设，对自噬这一核途径的特定操纵 在治疗与年龄相关的疾病方面有希望。对于K99期，我建议研究细胞质的作用 染色质通过自噬在调节衰老相关炎症中穿梭(目标1)。我进一步建议 使用体内衰老模型，研究人类衰老过程中慢性炎症的这一途径(目标2)。 在R00阶段，我计划研究一种染色质修饰物的自噬降解，它扮演着一个 在长寿中的重要作用(目标3)，并确定与以下相关的新的自噬核底物 自噬蛋白和调节衰老和衰老(目标4)。本研究将做出开创性的贡献 有助于我们从核稳态的角度理解哺乳动物的衰老，并可能有助于 在改善年龄相关疾病方面确定新的药物靶点。拟议的培训和 研究将极大地促进我过渡到一个独立的终身教员职位。

Human aging and a number of age-related diseases are associated with altered protein homeostasis, or proteostasis. Among the critical regulators of proteostasis is autophagy, an evolutionarily conserved membrane trafficking process that degrades a variety of cellular constituents through the lysosome. Autophagy is induced during starvation and calorie restriction, and is essential for maintaining cell and tissue integrity. While autophagy is well-known to degrade cytoplasmic materials, recently I have made the surprising discovery that mammalian autophagy is able to degrade nuclear constituents (Dou et al, Nature, 2015). The autophagy protein LC3 is present in the nucleus and directly interacts with the nuclear lamina protein Lamin B1, and associates with lamin-associated domains (LADs) on chromatin at the genome-wide level. This interaction mediates trafficking and degradation of Lamin B1 and associated heterochromatin, through a nucleus-to- cytoplasm transport process, leading to their digestion in cytoplasmic lysosomes. This lamina and chromatin autodigestion specifically occurs during cellular senescence, a stable form of cell-cycle arrest. Senescence is a specialized cell state in response to oncogene activation, which is beneficial in restraining tumorigenesis; however, senescence is also induced during aging, which contributes to age-related pathologies. I found that inhibiting autophagy or the LC3-Lamin B1 interaction prevents the degradation of Lamin B1 and extends cellular lifespan. These findings provide the first demonstration that mammalian autophagy has functional roles in maintaining homeostasis of the nucleus, suggests a new direction in understanding mammalian aging, and provokes numerous questions to be addressed. In this proposal, I plan to investigate this new perspective of nuclear autophagy, and to study its impact on chromatin and aging. My central hypothesis is that while autophagic degeneration of chromatin is an intrinsic tumor suppressive mechanism, paradoxically it is improperly adapted during aging and contributes to age-related pathologies. I also hypothesize that specific manipulation of this nuclear pathway of autophagy holds promise in treating age-related diseases. For the K99 phase, I propose to study the role of cytoplasmic chromatin shuttled by autophagy in mediating senescence-associated inflammation (Aim 1). I further propose to investigate this pathway in chronic inflammation as seen in human aging, using in vivo aging models (Aim 2). In the R00 phase, I plan to investigate the autophagic degradation of a chromatin modifier that plays an essential role in longevity (Aim 3), and to identify novel nuclear substrates of autophagy that associate with autophagy proteins and regulate senescence and aging (Aim 4). This study will make pioneering contributions to our understanding of mammalian aging from the perspective of nuclear homeostasis, and may help to identify new pharmaceutical targets in ameliorating age-associated disorders. The proposed training and research will greatly facilitate my transition to an independent tenured-track faculty position.