Secretion of mitochondria as a cellular quality control mechanism

项目摘要 在心脏中，线粒体的首要功能是满足跳动的高能量需求 通过氧化磷酸化提供ATP。然而，线粒体可以迅速变成 促死细胞器毫不奇怪，细胞已经发展出多种防御机制， 异常的线粒体会对细胞造成伤害。消除功能失调的线粒体的能力， 防止不必要的死亡在不能轻易替换的有丝分裂后肌细胞中尤其重要。是 众所周知，功能失调的线粒体被自噬体迅速隔离， 递送至溶酶体进行降解。最近的研究已经确定了细胞，也可以消除线粒体 通过Rab 9依赖的替代性自噬途径或通过Rab 5依赖的早期内体途径。 线粒体也可以直接被溶酶体摄取。很明显，多种线粒体清除途径 存在于细胞中，以防止其积累并确保存活。然而，这些降解途径 收敛于溶酶体水平，目前尚不清楚是否替代线粒体质量控制 当溶酶体功能受到损害时，存在通路。我们发现功能失调的线粒体 也可以在内部降解途径被淹没或受损时从细胞中分泌。我们 初步数据表明，具有受损的溶酶体降解的Rab 7-/-和LAMP 2-/-细胞仍然是 能够有效地消除去极化的线粒体。我们还发现循环细胞外 心肌梗死后血浆中含有线粒体的囊泡（EV），以及心脏特异性 基线时Rab 7和LAMP 2缺陷小鼠。EV的蛋白质组学分析结合Western blot分析 这表明线粒体位于源自内体途径的囊泡中。在本提案中，我们 将调查这一假设，即功能失调的线粒体是从电动汽车的细胞分泌的，这是一个假设， 代表心脏中的一个重要质量控制途径，可以在溶酶体被破坏时进行补偿。 不知所措或妥协这一假设将以两个具体目标进行检验。具体目标1将确定 含有线粒体的细胞外囊泡的起源和命运，并决定病理生理 诱导它们从肌细胞释放的条件。具体目标2将剖析分子机制 调节EV中线粒体的分泌。总的来说，这些研究将提供重要的新见解， 心肌线粒体消除的新替代机制。这些研究还将提供 深入了解这些EV是否可以作为心脏应激的早期诊断生物标志物， 疾病的发展。

Project summary In the heart, the primary function of mitochondria is to meet the high energy demand of the beating myocytes by providing ATP through oxidative phosphorylation. However, mitochondria can quickly change into death-promoting organelles. Not surprisingly, cells have developed multiple defense mechanisms against aberrant mitochondria that can cause harm to the cell. The ability to eliminate dysfunctional mitochondria and prevent unnecessary death is particularly important in post-mitotic myocytes that cannot be easily replaced. It is well established that dysfunctional mitochondria are rapidly sequestered by autophagosomes and subsequently delivered to lysosomes for degradation. Recent studies have identified cells that can also eliminate mitochondria via a Rab9-dependent alternative autophagy pathway or via a Rab5-dependent-early endosomal pathway. Mitochondria can also be directly taken up by lysosomes. Clearly, multiple pathways of mitochondrial elimination exist in cells to prevent their accumulation and ensure survival. However, these degradation pathways all converge at the level of the lysosomes and it is not clear whether alternative mitochondrial quality control pathways exists when lysosomal function is compromised. We have discovered that dysfunctional mitochondria can also be secreted from cells when internal degradation pathways are overwhelmed or impaired. Our preliminary data demonstrate that Rab7-/- and LAMP2-/- cells that have impaired lysosomal degradation are still able to efficiently eliminate depolarized mitochondria. We also found increased levels of circulating extracellular vesicles (EVs) containing mitochondria in plasma after a myocardial infarction, as well as in cardiac specific Rab7- and LAMP2-deficient mice at baseline. Proteomics analysis of EVs combined with Western blot analysis suggest that the mitochondria are in vesicles that originate from the endosomal pathway. In this proposal, we will investigate the hypothesis that dysfunctional mitochondria are secreted from cells in EVs and that this represent an important quality control pathway in the heart that can compensate when lysosomes are overwhelmed or compromised. This hypothesis will be tested with two specific aims. Specific aim 1 will identify the origin and fate of the extracellular vesicles containing mitochondria and determine the pathophysiological conditions that induce their release from myocytes. Specific aim 2 will dissect the molecular mechanisms regulating secretion of mitochondria in EVs. Overall, these studies will provide important new insights into a novel alternative mechanism of mitochondrial elimination in the myocardium. The studies will also provide insights into whether these EVs can potentially function as early diagnostic biomarkers of cardiac stress prior to development of disease.