Retrograde signaling pathways and changes in cardiac metabolism induced bymitochondrial dysfunction in Barth syndrome

Barth综合征（BTHS）是一种遗传性心肌病，由线粒体磷脂心磷脂（CL）生物合成缺陷引起。CL缺乏的心肌线粒体显示呼吸链的结构重塑，呼吸减少和活性氧（ROS）的产生增加。在这个项目中，我们将解决的假设，线粒体功能障碍是由一个逆行信号通路，并触发细胞代谢的适应性重塑。使用BTHS小鼠模型和患者来源的iPSC心肌细胞（iPSC-CM），我们将测试整合的应激反应途径（ISR）的诱导和应激诱导的转录因子ATF 5的稳定参与基因转录变化的假设。我们非常感兴趣的分子机制，如何逆行信号被功能失调的线粒体激活。我们将通过识别负责ISR通路激活的传感器激酶来剖析上游信号通路。通过干扰参与CL生物合成不同阶段的基因，我们将创建不同的CL库并监测ISR激活。为了分析ROS参与ISR激活，我们将通过表达植物替代氧化酶（AOX）来淬灭BTHS小鼠模型中的ROS。我们感兴趣的是稳定的逆行反应转录因子ATF 5的分子机制。ATF 5被输入到线粒体中，随后在线粒体未受影响的细胞中降解。使用体外输入试验，我们将测试假设，线粒体功能障碍诱导线粒体转运阻滞，允许ATF 5稳定和诱导核中的基因转录。我们将解决这些途径在心脏代谢重塑中的作用。脂肪酸在支持心脏组织的能量需求方面起着主导作用。我们的初步数据显示BTHS小鼠模型和患者来源的iPSC-CM中β-氧化的显著降低。我们将测试ISR信号诱导线粒体代谢重塑，从而减少脂肪酸氧化，这是特别容易ROS生成的假设。我们还测试了线粒体LONP 1蛋白酶在诱导呼吸链结构变化和交换细胞色素c氧化酶和呼吸链其他复合物的调节亚基中的作用。呼吸链重塑和ROS产生增加是许多呼吸系统疾病的常见现象。在这里，我们将阐明线粒体功能障碍如何通过逆行信号监测并触发适应性核反应的一般机制。

Barth syndrome (BTHS) is an inherited form of cardiomyopathy, caused by a defect in the biogenesis of the mitochondrial phospholipid cardiolipin (CL). CL deficient cardiac mitochondria show a structural remodeling of the respiratory chain, a decreased respiration and an increased generation of reactive oxygen species (ROS). In this project, we will address the hypothesis that mitochondrial dysfunction is sensed by a retrograde signaling pathway and triggers an adaptive remodeling of cellular metabolism. Using the BTHS mouse model and patient derived iPSC cardiomyocytes (iPSC-CM) we will test the hypothesis that the induction of the integrated stress response pathway (ISR) and the stabilization of the stress induced transcription factor ATF5 is involved in changes in gene transcription. We are highly interested in the molecular mechanism, how retrograde signaling is activated by dysfunctional mitochondria. We will dissect the upstream signaling pathways by identifying the sensor kinases, responsible for the activation of the ISR pathway. By interference with genes involved in different stages of CL biosynthesis, we will create different CL pools and monitor ISR activation. In order to analyze the involvement of ROS in ISR activation, we will quench ROS in the BTHS mouse model by the expression of the plant alternative oxidase (AOX). We are interested in the molecular mechanism of the stabilization of the retrograde response transcription factor ATF5. ATF5 is imported into mitochondria and subsequently degraded in cells with unaffected mitochondria. Using an in vitro import assay, we will test the hypothesis that mitochondrial dysfunction induces a block of mitochondrial transport allowing ATF5 to stabilize and induce gene transcription in the nucleus.We will address the role of these pathways in metabolic remodeling in the heart. Fatty acids play a predominant role in supporting the energy demand in cardiac tissue. Our preliminary data show a significant reduction in -oxidation in BTHS mouse model and patient derived iPSC-CM. We will test the hypothesis that ISR signaling induces a remodeling of mitochondrial metabolism, thereby reducing fatty acid oxidation, which is particularly prone to ROS-generation. We also test the role of the mitochondrial LONP1 protease in inducing structural changes in the respiratory chain and exchanging regulatory subunits of the cytochrome c oxidase and other complexes of the respiratory chain. Respiratory chain remodeling and increased ROS production are common to many mitochondriopathies. Here we will shed light into a general mechanism how mitochondrial dysfunction is monitored by retrograde signaling and triggers an adaptive nuclear response.