An interdisciplinary approach to elucidate mechanisms of muscle lipotoxicity

我们目睹了肥胖症患病率的急剧上升，肥胖症正推动全球2型糖尿病人数惊人地增加。针对这种疾病的早期阶段的合理治疗方法需要全面了解将胰岛素抵抗与过量热量消耗联系起来的机制。骨骼肌脂类蓄积、胰岛素抵抗和糖代谢受损之间的联系已被广泛认识，但这种联系的机制基础仍然难以捉摸。事实上，细胞内标签的积累可以与肌肉性能和代谢灵活性的改善相关。在R24种子资助期间，我们建立了一个统一的跨学科研究团队，进行了可行性和概念验证研究，并设计了一个完整的R24项目来解决这个问题。我们将验证一个中心假设，即心肌细胞脂肪堆积触发适应性和非适应性(脂毒性)反应，这些反应可以通过胰岛素信号依赖和非依赖性机制影响葡萄糖利用，这些反应之间的动态平衡决定了肌肉胰岛素抵抗的演变。该项目将利用无偏见的化学生物学和功能基因组学筛选的综合力量，由五个相互关联的具体目标组成。化学生物学(AIM 1)和功能基因组(AIM 2)筛查将使用富含过量脂肪酸的培养骨骼肌细胞进行。为了在体内有效地评估肌肉自主和非自主的影响，将使用肥胖的果蝇模型来快速验证这些基因(目标3)。系统集成组将监督对每个目标的研究产生的数据的收集、存储、过滤和分析，以建立基因、小分子修饰物和相应的靶途径的优先列表。在最初的代谢分类和优先排序之后，将进行深入的细胞和代谢特征的迭代过程以及代谢组、脂组和转录组分析，以确定代表相关心肌细胞扰动的适应性和非适应性亚类或“箱”的表型指纹或特征(目标4)。然后，将表型特征与从一系列健康和代谢性疾病队列中特征良好的人类志愿者那里收集的肌肉活检样本的相似特征进行比较(目标5)。该项目的长期目标是确定与肌肉脂肪毒性相关的新基因、途径和分子探针，为该领域提供有价值的假说资源，并建立针对胰岛素抵抗早期阶段的药物开发和生物标记物发现的管道。

We are witnessing a dramatic increase in the prevalence of obesity, which is driving an alarming increase in type 2 diabetes worldwide. Rational therapeutic approaches targeting the early stages of this disease continuum requires a comprehensive understanding of the mechanisms that link insulin resistance to excess caloric consumption. An association between skeletal muscle lipid accumulation, insulin resistance, and impaired glucose metabolism is widely recognized, yet the mechanistic underpinnings of the association remain elusive. Indeed, intramyocellular TAG accumulation can be associated with improved muscle performance and metabolic flexibility. During a period of R24 seed grant support, we have built a unified interdisciplinary research team, conducted feasibility and proof-of-concept studies, and designed a full R24 project to address this problem. We will test the central hypothesis that myocellular lipid accumulation triggers both adaptive and maladaptive (lipotoxic) responses, that these can influence glucose utilization via insulin signaling-dependent and -independent mechanisms, and that a dynamic balance between these responses determines the evolution of muscle insulin resistance. This project, which will harness the combined powers of unbiased chemical biology and functional genomics screening, is composed of five inter-connected Specific Aims. Chemical biology (Aim 1) and functional genomic (Aim 2) screens will be conducted using cultured skeletal myocytes loaded with excess fatty acid. To efficiently assess muscle autonomous vs. non-autonomous effects in vivo, a Drosophila model of obesity will be used to rapidly validate the genes (Aim 3). A Systems Integration Group will oversee the collection, storage, filtering, and analysis of the data generated by the studies of each Aim, to establish prioritized lists of genes, small molecule modifiers, and corresponding target pathways. After initial metabolic classification and prioritization, an iterative process of deep cellular and metabolic characterization together with metabolomic, lipidomic, and transcriptomic profiling, will be conducted to define phenotypic fingerprints or signatures representing adaptive and maladaptive sub-categories or "bins" of relevant myocyte perturbations (Aim 4). The phenotypic signatures will then be compared with similar profiles collected for muscle biopsy specimens from well-characterized human volunteers across a range of fitness and metabolic disease cohorts (Aim 5). The long-term goal of this project is to identify new genes, pathways, and molecular probes relevant to muscle lipotoxicity, serving as a valuable hypothesis-generating resource for the field and establishing a pipeline for drug development and biomarker discovery aimed at the earliest stages of insulin resistance.