Autophagy and Megamitochondria in Cardiac Aging and Heart Failure

项目摘要 随着发达国家的平均预期寿命持续增长，与年龄相关的疾病正在增加。 越来越普遍。衰老是心血管疾病的主要危险因素， 衰老包括肌细胞损失、纤维化和肥大，所有这些都导致 心脏病在分子水平上，细胞老化的特征是活性氧增加 (ROS)生产，线粒体功能障碍和受损蛋白质和细胞器的积累。心脏 肌细胞依靠自噬（一种溶酶体介导的降解途径）来清除毒性蛋白 从细胞环境中聚集和损坏的细胞器。越来越多的证据表明 相关的肌细胞自噬减少，对心脏功能和 健康然而，目前还不清楚为什么自噬会随着年龄的增长而下降，以及是否有特定的蛋白质或途径， 参与调节自噬的基因随着年龄而改变。线粒体功能障碍也是衰老的一个关键标志 并与包括心力衰竭在内的许多与年龄相关的病理学有关。此外，扩大或 巨线粒体通常存在于衰老的组织中，但它们对衰老过程的潜在贡献， 疾病的发展仍然未知。我们已经证实，自噬活性在老年小鼠中降低， 心脏与泛素化线粒体的积累有关。我们的初步数据还表明， 老年心脏自噬活性的降低是由于Atg9b表达的改变，Atg9b是心脏自噬的关键调节因子， 自噬体的形成和延伸。我们还发现，老年小鼠的心脏含有大量的 线粒体数量增多。为什么这些巨线粒体在心脏中随着年龄的增长而形成， 导致衰老的原因目前尚不清楚。在这个建议中，我们将检验一个假设， 衰老心脏中自噬体形成和线粒体清除的下降导致融合增加 在功能失调和健康的线粒体之间建立联系，试图稀释受损的成分。随着时间的推移， 这些巨线粒体积累了更高水平的损伤。它们的功能变得更弱， 增加的ROS，这直接导致心脏衰老过程。这一假设将用两个 具体目标。具体目标1将剖析与年龄相关的自噬下降的机制。 具体目标2将描述衰老过程中线粒体形态与自噬之间的相互作用。 我们还将研究恢复Atg9b是否会增强老年心脏中的基线自噬，以及是否 减少线粒体ROS的产生将防止或延迟与年龄相关的自噬下降， 消除有害的巨线粒体的形成。总的来说，这些研究将进一步加深我们对 衰老过程的分子机制，并帮助确定干预措施，以保护线粒体 体内平衡和防止疾病发展。

Project summary As average life expectancy continues to rise in the developed world, age associated pathologies are increasingly prevalent. Aging is a major risk factor for cardiovascular diseases and the hallmarks of cardiac aging include loss of myocytes, fibrosis and hypertrophy, all of which contribute to increased incidence of cardiac disease. At the molecular level, cellular aging is characterized by increased reactive oxygen species (ROS) production, mitochondrial dysfunction and accumulation of damaged proteins and organelles. Cardiac myocytes rely upon autophagy, a lysosome-mediated degradation pathway, to remove toxic protein aggregates and damaged organelles from the cellular milieu. Increasing lines of evidence point to an age- associated decrease in myocyte autophagy, with predictably negative consequences for cardiac function and health. However, it is still unclear why autophagy declines with age and whether specific proteins or pathways involved in regulating autophagy are altered with age. Mitochondrial dysfunction is also a key hallmark of aging and has been linked to a number of age-related pathologies, including heart failure. In addition, enlarged or megamitochondria are often present in aged tissues, but their potential contribution to the aging process and disease development remain unknown. We have confirmed that autophagic activity is reduced in aged mouse hearts which correlates with accumulation of ubiquitinated mitochondria. Our preliminary data also suggest that the decrease in autophagic activity in the aged heart is due to altered expression of Atg9b, a key regulator of autophagosome formation and elongation. We also found that the aged mouse heart contains a substantial number of enlarged mitochondria. Why these megamitochondria form with age in the heart and whether they contribute to the aging process are currently unknown. In this proposal, we will examine the hypothesis that a decline in autophagosome formation and mitochondrial clearance in the aging heart leads to increased fusion between dysfunctional and healthy mitochondria in an attempt to dilute damaged components. Over time, these megamitochondria accumulate increased levels of damage. They become less functional and generate increased ROS, which directly contribute to the cardiac aging process. This hypothesis will be tested with two specific aims. Specific aim 1 will dissect the mechanism underlying the age-associated decline in autophagy. Specific aim 2 will characterize the interplay between mitochondrial morphology and autophagy during aging. We will also investigate if restoring Atg9b will enhance baseline autophagy in the aged hearts and whether reduced mitochondrial ROS production will prevent or delay the age associated decline in autophagy and abrogate formation of harmful megamitochondria. Overall, these studies will further our understanding of the molecular mechanism underlying the aging process and help identify interventions to preserve mitochondrial homeostasis and prevent development of disease.