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

人类衰老和许多与年龄有关的疾病与蛋白质稳态的改变有关， 或蛋白质稳态。蛋白质稳态的关键调节因子之一是自噬，一种进化上保守的蛋白质自噬机制。 通过溶酶体降解多种细胞成分的膜运输过程。自噬 在饥饿和热量限制期间被诱导，并且对于维持细胞和组织的完整性至关重要。 虽然自噬是众所周知的降解细胞质材料，最近我做了令人惊讶的 发现哺乳动物自噬能够降解核成分（Dou等人，Nature，2015）。的 自噬蛋白LC 3存在于细胞核中并直接与核纤层蛋白核纤层蛋白B1相互作用， 并在全基因组水平上与染色质上的核纤层蛋白相关结构域（LAD）结合。这种相互作用 介导核纤层蛋白B1和相关异染色质的运输和降解，通过核- 细胞质转运过程，导致其在细胞质溶酶体中消化。这层和染色质 自身消化特别发生在细胞衰老期间，细胞周期停滞的稳定形式。衰老是一种 响应于癌基因激活的特化细胞状态，这有利于抑制肿瘤发生; 然而，衰老过程中也会引起衰老，这会导致与年龄有关的病理。我发现 抑制自噬或LC 3-核纤层蛋白B1相互作用可防止核纤层蛋白B1的降解， 细胞寿命这些发现首次证明了哺乳动物自噬具有功能性 在维持细胞核内稳态中的作用，为理解哺乳动物衰老提供了新的方向， 并引发了许多有待解决的问题。 在这个提议中，我计划从这个新的角度来研究核自噬，并研究它的影响 关于染色质和衰老。我的中心假设是，虽然染色质的自噬性变性是一种 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， 与年龄有关的疾病我还假设，对这种细胞核自噬途径的特异性操纵 有望治疗与年龄有关的疾病。对于K99期，我建议研究细胞质的作用， 自噬穿梭染色质介导衰老相关炎症（Aim 1）。我进一步提议 使用体内老化模型研究在人类老化中所见的慢性炎症中的该途径（目的2）。 在R 00阶段，我计划研究一种染色质修饰剂的自噬降解， 在长寿中的重要作用（目标3），并确定与细胞自噬相关的新的核底物。 自噬蛋白并调节衰老和衰老（目标4）。这项研究将作出开拓性的贡献 从核内稳态的角度来理解哺乳动物的衰老，并可能有助于 确定改善年龄相关疾病的新药物靶点。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职。

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.