Signaling from sarcomere to mitochondria: a new paradigm for optimal muscle performance

肌肉的功能使动物能够移动，保持姿势，并进行心脏跳动。肌肉活动所需的大部分能量，由一种叫做ATP的小化学物质储存和释放，由细胞的“发电站”——线粒体提供。预计在这些线粒体和产生肌肉力量的分子机制肌原纤维之间存在着通信，从而使能量产生满足能量需求。但是，到目前为止，还没有这种来文的报告。参与该项目的实验室研究人员已经为这种交流提供了证据，他们现在正试图了解潜在的分子机制。为了增加非科学家对科学的理解，该项目还将：(1)开设一门本科课程，“音乐和生物的结构”，该课程将研究音乐和生物系统中结构和形式的相似性；(2)每年举办一次为期一天的研讨会，向全校开放，音乐/科学双学位学生将(a)发表非科学家可以理解的研究报告；(b)表演一篇受科学研究启发而写的作文。在横纹肌中，肌肉收缩需要大量的ATP，而这些ATP主要由线粒体提供。线粒体形成一个复杂的3D网络，紧挨着肌原纤维/SR/ t小管。然而，线粒体网络与收缩机制的结构协调机制，以及将收缩的能量需求整合到能量生产机制的机制尚不清楚。研究人员关于秀丽隐杆线虫巨肌合成蛋白UNC-89（人体内的隐蛋白）的数据提供了新的见解。unc-89突变虫整体运动能力下降，肌节和肌浆网（SR）组织紊乱。UNC-89蛋白定位于肉瘤m系，是具有两个蛋白激酶结构域（PK1和PK2）的多结构域蛋白。使用CRISPR/Cas9构建表达正常水平的UNC-89的线虫，其PK2激酶结构域失活。与所有其他unc-89突变体不同，unc-89 PK2激酶死亡突变体具有正常的肌节结构、正常的SR组织以及正常的全身运动和力产生。令人惊讶的是，UNC-89 PK2激酶死亡突变的肌肉线粒体碎片化，产生更多的ATP，并且它们的线粒体呼吸水平高于野生型。这些结果表明：(1)来自肉瘤蛋白UNC-89的激酶活性调节线粒体形态和能量学；(2)与疾病或衰老中观察到的线粒体断裂和功能障碍不同，这种断裂改善了线粒体功能。据推测，UNC-89作为一个信号平台，通过线粒体形态和能量输出协调肌肉结构和活动，而UNC-89 PK2磷酸化了该信号传导中的一个关键蛋白。为了验证这些假设，本研究将：(1)确定UNC-89激酶死亡突变体中线粒体片段化和功能增强的机制；(2)确定UNC-89蛋白激酶肉瘤-线粒体信号网络。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Muscle function allows an animal to move, to maintain posture, and to perform heart pumping. Most of the energy required for muscle activity, stored and released from the small chemical called ATP, is provided by the “powerhouses” of cells, the mitochondria. It is expected that there is communication between these mitochondria and the molecular machinery that produces muscle force, the myofibrils, so that energy production meets energy demand. However, to date, such communication has not been reported. Investigators from the laboratory engaged in this project have provided evidence for this communication, and they now seek to understand the underlying molecular mechanisms. To increase the understanding of science by non-scientists, the project will also: (1) create an undergraduate course, “Structure in Music and Biology”, which will examine similarities in structure and form in music and in biological systems, and (2) conduct an annual day-long symposium open to the entire university, in which music/science double majors will (a) present a talk about their research understandable by non-scientists; and (b) perform a composition that they have written that was inspired by their scientific research.In striated muscle, large amounts of ATP are required for muscle contraction and this ATP is mostly supplied by mitochondria. The mitochondria form a complex 3D network closely apposed to the myofibril/SR/T-tubules. The mechanisms, however, underlying the structural coordination of the mitochondrial network with the contractile machinery, and mechanisms that integrate the energetic demands of contraction to the energy production machinery are unknown. The investigator’s data on the C. elegans giant sarcomeric protein UNC-89 (obscurin in humans), provide novel insight. unc-89 mutant worms show reduced whole worm locomotion and have disorganized sarcomeres and sarcoplasmic reticulum (SR). UNC-89 proteins localize to sarcomeric M-lines, and are multidomain proteins having two protein kinase domains (PK1 and PK2). CRISPR/Cas9 was used to create nematodes that express normal levels of UNC-89 with an inactive PK2 kinase domain. Unlike all other unc-89 mutants, UNC-89 PK2 kinase dead mutants have normal sarcomere structure, normal SR organization, and normal whole-body locomotion and force production. Surprisingly, UNC-89 PK2 kinase dead mutant muscle have fragmented mitochondria, produce more ATP, and their mitochondria respire at higher than wild type levels. These results suggest: (1) the kinase activity from sarcomeric protein UNC-89 modulates mitochondrial morphology and energetics, and (2) unlike mitochondrial fragmentation and dysfunction observed in disease or aging, this fragmentation improves mitochondrial function. It is hypothesized that UNC-89 serves as a signaling platform to coordinate muscle structure and activity with mitochondrial morphology and energy output, and that UNC-89 PK2 phosphorylates a key protein in this signaling. To test these hypotheses, the research will: (1) Determine the mechanism(s) by which mitochondria are fragmented and are functionally enhanced in UNC-89 kinase dead mutants, and (2) Determine the UNC-89 protein kinase sarcomere-to-mitochondria signaling network.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.