An interdisciplinary approach to elucidate mechanisms of muscle lipotoxicity

我们正在目睹肥胖症患病率的急剧上升，这导致全球2型糖尿病的发病率惊人地上升。针对这种疾病连续体早期阶段的合理治疗方法需要全面了解胰岛素抵抗与过量热量消耗之间的联系机制。骨骼肌脂质积累、胰岛素抵抗和糖代谢受损之间的关联已被广泛认识，但其机制基础仍不明确。事实上，细胞内TAG的积累可以与改善肌肉性能和代谢灵活性有关。在R24种子基金支持期间，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。我们将验证心肌细胞脂质积累触发适应性和不适应（脂毒性）反应的中心假设，这些反应可以通过胰岛素信号依赖和独立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。该项目将利用公正的化学生物学和功能基因组学筛选的综合力量，由五个相互关联的特定目标组成。化学生物学（Aim 1）和功能基因组学（Aim 2）筛选将使用装载过量脂肪酸的培养骨骼肌细胞进行。为了有效地评估肌肉自主与非自主在体内的作用，肥胖的果蝇模型将被用来快速验证基因（目的3）。系统集成组将监督每个Aim研究产生的数据的收集、存储、过滤和分析，以建立基因、小分子修饰剂和相应目标途径的优先列表。在最初的代谢分类和优先排序之后，将进行深层细胞和代谢表征以及代谢组学、脂质组学和转录组学分析的迭代过程，以定义代表适应性和非适应性亚类别或相关肌细胞扰动“桶”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具有良好特征的人类志愿者的肌肉活检标本收集的相似特征进行比较（目的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设生成资源，并为针对胰岛素抵抗早期阶段的药物开发和生物标志物发现建立管道。

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.