Regulation of Fetal Skeletal Muscle Growth in IUGR

项目摘要 我们的目标是改善骨骼肌生长和身体组成的胎儿，新生儿，和成人受影响的 宫内生长受限（IUGR）。胎儿骨骼肌的生长是非常有限的，由于胎盘 不足，并导致终身减少肌肉质量（肌肉减少症）和代谢疾病的风险，使 在围产期恢复肌肉质量是一个高度优先事项。在项目前期，我们 在一个高度相关的IUGR绵羊模型中发现了胎儿骨骼肌生长的多种缺陷， 肌肉蛋白质合成（MPS）率，相对于大脑和全身重量的肌肉质量较低， 与正常生长的对照组相比，肌纤维的数量较低，总肌纤维较少。 根据我们的初步数据，我们已经确定了支链氨基酸（BCAA）内的适应性。 导致IUGR胎儿MPS较低的子宫内膜异位症。IUGR后肢的体重特异性BCAA摄取率 尽管循环中BCAA浓度正常，但Na + K +-ATP酶活性降低可能导致 驱动支链氨基酸进入肌细胞。支链氨基转移酶（BCAT）蛋白表达较高， BCAA催化的第一步，导致丙氨酸和谷氨酰胺的重新合成， 再生、补侧和能量生产。尽管我们最近取得了进展，但是， 关于胎盘功能不全对IUGR肌细胞的编程机制， 减少BCAA的摄入，增加BCAA的催化量。此外，不知道在IUGR期间， 妊娠这些机制成为内在的肌细胞或如何可以防止和/或逆转， 促进肌肉生长。我们组建了一支由高素质的新陈代谢专家组成的研究团队， 最先进的代谢组学和蛋白质组学技术来填补这些知识空白。我们将检验这个假设 低Na + K +-ATP酶和高BCAT活性是胎儿心肌细胞固有的， 并在IUGR妊娠结束时限制MPS，但靶向治疗（L-丙氨酰-L-谷氨酰胺，AG） 在关键的发展窗口将改善这些缺陷，以增加MPS。在目标1中，我们将确定 减少MPS的细胞机制，并测试这些适应性是内在的程度， 肌细胞和/或外源性循环因子诱导的IUGR胎儿。在目标2中，我们将解决MPS 在IUGR怀孕期间变得有限。此信息对于通知 怀孕期间的治疗旨在促进胎儿生长。在目标3中，我们将测试AG输注的能力 进入IUGR胎儿，激活Na + K +-ATP酶，刺激BCAA摄取，并逆转BCAA催化， 肌肉注射支链氨基酸治疗多磺酸粘多糖总之，该提案将解决有关BCAA如何 在胎盘功能不全的胎儿中，当肌纤维形成时， 生长和肥大率是生命周期中最高的。这些研究是必要的 这是设计新方法恢复肌肉生长的先决条件。

PROJECT ABSTRACT Our goal is to improve skeletal muscle growth and body composition in the fetus, neonate, and adult affected by intrauterine growth restriction (IUGR). Fetal skeletal muscle growth is profoundly limited as a result of placental insufficiency and leads to lifelong reductions in muscle mass (sarcopenia) and metabolic disease risk, making restoration of muscle mass during the perinatal period a high priority. During the previous project period, we found multiple defects in fetal skeletal muscle growth in a highly relevant sheep model of IUGR, including lower muscle protein synthesis (MPS) rates, lower muscle mass relative to brain and whole-body weights, smaller myofibers with lower myonuclear number, and fewer total myofibers compared to normally-growing controls. Based on our preliminary data, we have identified adaptations within branched-chain amino acid (BCAA) catabolism that result in lower MPS in the IUGR fetus. Weight-specific BCAA uptake rates by the IUGR hindlimb are reduced despite normal circulating BCAA concentrations, the likely result of lower Na+K+-ATPase activity to drive BCAA into the myocyte. Branched-chain aminotransferase (BCAT) protein expression is higher, which is the first step in BCAA catabolism and results in de novo alanine and glutamine synthesis to support gluconeogenesis, anapleurosis, and energy production. Despite our recent progress, however, critical knowledge gaps remain regarding the mechanisms by which placental insufficiency programs the IUGR myocyte to reduce BCAA uptake and increase BCAA catabolism. Furthermore, it is not known when during an IUGR gestation these mechanisms become intrinsic to the myocyte or how they may be prevented and/or reversed to improve muscle growth. We have assembled a research team of highly qualified experts in metabolism and state-of-the-art metabolomic and proteomic techniques to fill these knowledge gaps. We will test the hypothesis that lower Na+K+-ATPase and higher BCAT activity are intrinsic to the fetal myocyte to increase BCAA catabolism and limit MPS by the end of an IUGR gestation, but that a targeted therapy (L-alanyl-L-glutamine, AG) delivered during a critical developmental window will ameliorate these defects to increase MPS. In Aim 1, we will determine the cellular mechanisms that reduce MPS and test the extent to which these adaptations are intrinsic to the myocyte and/or induced by extrinsic circulating factors the IUGR fetus. In Aim 2, we will address when MPS becomes limited during the course of an IUGR pregnancy. This information is critical to inform the timing of therapies during pregnancy aimed to increase fetal growth. In Aim 3, we will test the capacity of an AG infusion into the IUGR fetus to activate Na+K+-ATPase, stimulate BCAA uptake, and reverse BCAA catabolism to increase intramuscular BCAA for MPS. In summary, this proposal will address gaps in knowledge about how BCAA utilization is regulated in the fetus exposed to placental insufficiency when myofibers are forming, myonuclei are accreting, and hypertrophy rates are some of the highest during the lifespan. These studies are a necessary prerequisite for designing novel approaches to restore muscle growth.