Calcium homeostasis and cellular fitness in sepsis

摘要 每年有200万美国人因败血症住院，三分之一的人死亡。然而，那些幸存下来的， 没有治愈。神经认知障碍的发生率高达50%，认知能力下降持续长达8年。 脓毒症住院治疗占计划外再入院的比例高于心肌梗死患者。 梗塞、心力衰竭和COPD。败血症幸存者的五年死亡率超过心力衰竭， 中风这种持续健康损失的机制仍有待确定。我们假设 在脓毒症的早期，作为一种适应性机制， 未来的环境压力，如复发性败血症。这些结构性变化给我们带来了持久的变化， 支持细胞表型所必需的线粒体钙（Ca 2+）稳态和代谢， 对于多细胞生物体来说，这些是难以耐受的，并且是健康持续丧失的基础。 我们的实验室花了近二十年的时间研究脓毒症，以阐明钙依赖性机制， 调节线粒体生物学以平衡Ca 2+稳态和ATP生成并保持细胞健康。 我们已经证明，在脓毒症后早期，线粒体去极化产生Ca 2+信号。成员 Ca 2 + /钙调素依赖性蛋白激酶（CaMK）家族参与这些Ca 2+信号的传递， 串联介导线粒体分裂，线粒体自噬和氧化代谢的适应性变化，以减少 细胞损伤最近，我们观察到脓毒症重组线粒体钙单向转运体 (MCU)复杂，对线粒体和细胞Ca 2+稳态造成持久的变化， 代谢，扰乱整个生物体的细胞和组织功能。我们建议， 对脓毒症的“学习”反应，细胞重构MCU复合物以对抗Ca 2+的潜力 超负荷与未来的侮辱;这赋予持久的改变Ca 2+稳态，氧化 代谢和组织表型。采用下呼吸道和腹腔感染模型， 相关人体样本，我们提出以下目标： 目标1.在小鼠和人类中研究重组的MCU复合物如何改变Ca 2+稳态， 氧化代谢，从而包括生物体的每个组织的表型。 目标二。明确线粒体自噬和蛋白质通过溶酶体降解的机制， 蛋白酶体作为小鼠模型中MICU 1表达持续缺失的根本原因 脓毒症和人脓毒症幸存者。 这项新的实验工作将提供基础知识，以了解如何控制机制， 线粒体Ca 2+和代谢在脓毒症期间被重构，从而成为细胞内Ca 2+持续丧失的基础。 表型，导致健康状况逐渐丧失和生存期缩短。

ABSTRACT Two million Americans are hospitalized for sepsis each year, and 1 in 3 die. Those that survive, however, are not cured. Neurocognitive disorders occur in up to 50%, and cognitive decline continues for up to 8 years. Sepsis hospitalizations account for a higher proportion of unplanned readmissions than those for myocardial infarction, heart failure, and COPD. Five-year mortality for sepsis survivors exceeds that for heart failure and stroke. The mechanisms underlying this persistent loss of health remain to be defined. We hypothesize that early during sepsis the mitochondrion is restructured as an adaptive mechanism to protect the cell against any future environmental stress, such as recurrent sepsis. These structural changes impart lasting alterations to the mitochondrial calcium (Ca2+) homeostasis and metabolism necessary to support a cellular phenotype, which for a multicellular organism are poorly tolerated and underlie a persistent loss of health. Our lab has spent nearly two decades studying sepsis to elucidate the Ca2+-dependent mechanisms that regulate mitochondrial biology to balance Ca2+ homeostasis and ATP generation and preserve cellular health. We have shown that early after sepsis, mitochondrial depolarization generates a Ca2+ signal. Members of the family of Ca2+ /calmodulin-dependent protein kinases (CaMK) transduce these Ca2+ signals and work in tandem to mediate adaptive changes in mitochondrial fission, mitophagy, and oxidative metabolism to lessen cellular damage. More recently, we observed that sepsis restructures the mitochondrial calcium uniporter (MCU) complex, imposing long-lasting changes to mitochondrial and cellular Ca2+ homeostasis and metabolism that perturb cellular and tissue function across the entire organism. We propose that as a ‘learned’ response to sepsis, the cell restructures the MCU complex to counter the potential for Ca2+ overload with future insult; this imparts long-lasting alterations in Ca2+ homeostasis, oxidative metabolism, and tissue phenotype. Using models of lower-respiratory tract and intraperitoneal infection and correlative human samples, we propose the following aims: Aim 1. To study in mice and humans how a restructured MCU complex alters Ca2+ homeostasis and oxidative metabolism and thereby, the phenotype of each tissue comprising the organism. Aim 2. To define the mechanisms of mitophagy and protein degradation through the lysosome and proteasome as underlying causes of the persistent loss of MICU1 expression in murine models of sepsis and in human sepsis survivors. This new experimental work will provide foundational knowledge as to how the mechanisms governing mitochondrial Ca2+ and metabolism are restructured during sepsis to underlie a persistent loss of cellular phenotype that leads to a progressive loss of health and shortened survival.