Receptor-mediated glucose sensing and skeletal muscle function

项目摘要 骨骼肌是2型糖尿病（T2 D）期间代谢功能障碍发展的中心， 肥胖此外，这些条件往往伴随着加速肌肉损失，尽管存在 营养过剩。这表明营养感应机制与分子途径解偶联， 控制肌肉的可塑性例如，肌内烟酰胺腺嘌呤二核苷酸（NAD）的消耗是 与骨骼肌损失和功能障碍有关，而恢复或增加其水平的策略可以逆转 这个发病机制。特别地，聚（ADP-核糖）聚合酶1的遗传或药理学抑制 （PARP 1），一个主要的NAD消费者，通过增加NAD的可用性和增加肌肉的健康。 NAD依赖性去乙酰化酶sirtuin-1（SIRT 1）的活化。因此，识别连接 能量代谢对PARP 1活性的调节可以导致创新疗法的发展， 预防或治疗肌肉退化和代谢功能障碍。初步数据显示， 甜味受体（STR）对循环葡萄糖的直接感知调节PARP 1活性以控制 骨骼肌的适应潜能。具体地，T1 r2基因的全身或骨骼肌特异性缺失 STRs（T1 R2-KO）增强线粒体功能，氧化能力，运动耐量，并诱导轻度 肌纤维大小增加。这些改善与PARP 1活性减弱，NAD库增加， 并增强葡萄糖对核苷酸生物合成的利用。因此，T1 R2-KO小鼠受到保护， 与饮食引起的肥胖相关的代谢紊乱，包括肌肉质量损失。因此， 假设T1 R2受体是葡萄糖可用性的组成性传感器，以调节细胞内 控制骨骼肌可塑性代谢基础的途径。这一假设是通过 使用具有T1 r2基因的组成型或诱导型肌肉特异性缺失的小鼠的综合研究：1） 阐明T1 R2信号网络在肌肉生物能量学和功能调节中的作用。 具体而言，a）探测导致PARP 1调节和NAD生物利用度的信号传导途径，B）鉴定 SIRT 1和2的NAD依赖性激活的下游效应物，c）评估STR在SIRT 1和2中的作用， 调节底物利用，和d）确定STR信号传导和建立的 细胞内能量传感器（即AMPK、mTORC 1、Akt）。2)研究T1 R2介导的葡萄糖的作用 在肌肉质量的调节中的感知。具体地，a）评估诱导性缺失的生理效应， 成年骨骼肌中的STR信号传导以模拟靶向药物治疗的纵向效应 STR，B）定义STR信号传导对响应于治疗的肌肉质量适应的贡献， 诱导肌肉肥大或萎缩，c）肌肉发育过程中T1 r2基因时空表达 和生长，以及d）STR信号传导在出生后肌肉生长过程中的贡献。 通过评估形态学、信号传导和功能性肌肉适应性来评估生长。 .

PROJECT SUMMARY Skeletal muscle is central to the development of metabolic dysfunction during type 2 diabetes (T2D) and obesity. In addition, these conditions are often accompanied by accelerated muscle loss despite the presence of nutrient excess. This suggests uncoupling of nutrient sensing mechanisms with the molecular pathways that control muscle plasticity. For instance, depletion of intramuscular nicotinamide adenine dinucleotide (NAD) is linked to skeletal muscle loss and dysfunction, while strategies that restore or increase its levels can reverse this pathogenesis. Particularly, genetic or pharmacological inhibition of poly(ADP-ribose) polymerases 1 (PARP1), a major NAD consumer, improves muscle fitness through increases in NAD availability and the activation of NAD-dependent deacetylase sirtuin-1 (SIRT1). Thus, identifying physiological pathways that link energy metabolism to the regulation of PARP1 activity can lead to the development of innovative therapies for the prevention or treatment of muscle degeneration and metabolic dysfunction. Preliminary data suggest that direct sensing of circulating glucose by sweet taste receptors (STRs) regulates PARP1 activity to control the adaptive potential of skeletal muscle. Specifically, whole body or skeletal muscle-specific deletion of T1r2 gene of STRs (T1R2-KO) enhances mitochondrial function, oxidative capacity, exercise tolerance, and induces mild increases in myofiber size. These improvements are linked to attenuated PARP1 activity, increased NAD pool, and enhanced glucose utilization towards nucleotide biosynthesis. Consequently, T1R2-KO mice are protected from metabolic derangements associated with diet-induced obesity, including muscle mass loss. Thus, it was hypothesized that the T1R2 receptor is a constitutive sensor of glucose availability to adjust intracellular pathways that control the metabolic basis of skeletal muscle plasticity. This hypothesis is tested through comprehensive studies using mice with constitutive or inducible muscle-specific deletion of the T1r2 gene to: 1) Elucidate the role of T1R2 signaling network in the regulation of muscle bioenergetics and function. Specifically, a) probe signaling pathway leading to PARP1 regulation and NAD bioavailability, b) identify downstream effectors of NAD-dependent activation of SIRT1 and 2, c) assess contributions of STRs in the regulation of substrate utilization, and d) determine interactions between STR signaling and established intracellular energy sensors (i.e. AMPK, mTORC1, Akt). 2) Investigate contributions of T1R2-mediated glucose sensing in the regulation of muscle mass. Specifically, a) assess physiological effects of inducible deletion of STR signaling in adult skeletal muscle to mimic longitudinal effects of pharmacological treatments targeting STRs, b) define contributions of STR signaling to muscle mass adaptations in response to treatments that induce muscle hypertrophy or atrophy, c) spatiotemporal expression of T1r2 gene during muscle development and growth using muscle-specific reporter mice, and d) contributions of STR signaling during postnatal muscle growth through the assessment of morphological, signaling and functional muscle adaptations. .