HORMONAL REGULATION OF NEONATAL MUSCLE PROTEIN SYNTHESIS

长期目标是确定激素和营养素相互作用调节新生儿骨骼肌蛋白沉积高速率的机制，并确定败血症如何改变这些机制。 其目标是确定新的策略，以优化营养利用的生长迟缓和败血症婴儿的成长。骨骼肌质量的快速增长是新生儿生长的一个特别重要的特征。 先前的研究表明，正常新生儿中喂养诱导的肌肉蛋白质合成刺激涉及胰岛素和氨基酸的调节。 然而，由于正常新生儿肌肉蛋白质合成对胰岛素和氨基酸非常敏感，因此无法辨别这两种合成代谢药物是否相互作用以调节肌肉蛋白质合成。 脓毒症对新生儿的发病率和死亡率有很大的影响，而新生儿是一个肌肉蛋白储备有限的群体。激素变化和底物缺乏可能导致脓毒症发生的肌肉萎缩。假设是：1）氨基酸增强新生儿肌肉蛋白质合成对胰岛素水平的敏感性，2）氨基酸和胰岛素的相互作用反映了它们对真核起始因子（eIF）和信号激酶活性的独立作用，3）脓毒症通过肿瘤坏死因子α（TNF α）的相互作用抑制新生儿肌肉蛋白质合成。（TNF α）与胰岛素介导的蛋白质合成有关，这种作用可以通过氨基酸来规避。提出以下目标来解决这些假设：在目标1中，肌肉蛋白质合成胰岛素的剂量反应和氨基酸对这种反应的影响将在正常新生儿中确定。 为了实现这一目标，将在7日龄猪中进行研究，使用肌肉蛋白质合成的直接动力学测量和新型酶-底物钳技术的改进。 在目标2中，将确定胰岛素和氨基酸对关键eIF活性的影响。 为了实现这一点，将使用来自目标1中实验的肌肉来确定蛋白质合成速率、参与Met-tRNA和mRNA与40 S核糖体亚基结合的eIF的活性以及信号传导激酶的活化之间的定量关系。 这将确定体内胰岛素和氨基酸调节的特定翻译过程。 在目标3中，将确定施用内毒素、TNF α、抗细胞因子治疗和增强氨基酸供应后肌肉蛋白质合成对胰岛素的反应。 这些研究将确定激素、细胞因子和营养素在新生儿败血症诱导的肌肉萎缩中的作用。 氨基酸管理规避败血症诱导的胰岛素抵抗的肌肉蛋白质合成的实际效果将被确定。

The long-term objectives are to identify the mechanisms by which hormones and nutrients interact to regulate the high rate of skeletal muscle protein deposition in the neonate, and to determine how these mechanisms are altered by sepsis. The goal is to identify new strategies to optimize nutrient utilization for growth in growth-retarded and septic infants. Rapid accretion of skeletal muscle mass is a particularly important characteristic of neonatal growth. Previous work has shown that the feeding-induced stimulation of muscle protein synthesis in normal neonates involves regulation by both insulin and amino acids. However, because of the exquisite sensitivity of muscle protein synthesis to insulin and amino acids in the normal neonate, it could not be discerned whether both anabolic agents interact to regulate muscle protein synthesis. Sepsis contributes substantially to the morbidity and mortality of neonates, a population with limited muscle protein stores. Hormonal changes and substrate deficiency likely contribute to the muscle wasting that occurs with sepsis. The hypotheses are: 1) amino acids enhance the sensitivity of muscle protein synthesis to insulin levels in neonates, 2) the interaction of amino acids and insulin reflects their independent effects on the activity of eukaryotic initiation factors (eIFs) and signaling kinases, and 3) sepsis inhibits muscle protein synthesis in neonates via an interaction of tumor necrosis factor alpha (TNFalpha) with insulin-mediated protein synthesis, an effect that can be circumvented by amino acids. The following aims are proposed to address these hypotheses: In Aim 1, the dose response of muscle protein synthesis to insulin and the effect of amino acids on this response will be determined in normal neonates. To achieve this, studies will be performed in 7-d-old pigs using direct kinetic measurement of muscle protein synthesis and refinements of a novel hormone-substrate clamp technique. In Aim 2, the effects of insulin and amino acids on the activity of key eIFs will be determined. To achieve this, muscles from the experiments in Aim 1 will be used to determine the quantitative relationships among protein synthesis rates, the activity of the eIFs that are involved in the binding of Met-tRNA and mRNA to the 40S ribosomal subunit, and the activation of signaling kinases. This will identify the specific translational processes regulated by insulin and amino acids in vivo. In Aim 3, the response of muscle protein synthesis to insulin following administration of endotoxin, TNFalpha, anti-cytokine therapy, and enhanced amino acid supply will be determined. These studies will identify the role of hormones, cytokines, and nutrients in the sepsis-induced muscle wasting in neonates. The practical efficacy of amino acid administration to circumvent the sepsis-induced insulin resistance of muscle protein synthesis will be identified.