BACKGROUND The degradation of the steppe of Inner Mongolia, due to overgrazing, has resulted in ecosystem damage as well as extensive reductions in sheep production. The growth performance of sheep is greatly reduced because of overgrazing, which triggers massive economic losses every year. The liver is an essential organ that has very important roles in multiple functions, such as nutrient metabolism, immunity and others, which are closely related to animal growth. However, to our knowledge, no detailed studies have evaluated hepatic metabolism adaption in sheep due to overgrazing. The molecular mechanisms that underlie these effects remain unclear. METHODS In the present study, our group applied isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic analysis to investigate changes in the protein profiles of sheep hepatic tissues when nutrition was reduced due to overgrazing (12.0 sheep/ha), with the goal of characterizing the molecular mechanisms of hepatic metabolism adaption in sheep in an overgrazing condition. RESULTS The body weight daily gain of sheep was greatly decreased due to overgrazing. Overall, 41 proteins were found to be differentially abundant in the hepatic tissue between a light grazing group and an overgrazing group. Most of the differentially expressed proteins identified are involved in protein metabolism, transcriptional and translational regulation, and immune response. In particular, the altered abundance of kynureninase (KYNU) and HAL (histidine ammonia-lyase) involved in protein metabolic function, integrated with the changes of serum levels of blood urea nitrogen (BUN) and glucose (GLU), suggest that overgrazing triggers a shift in energy resources from carbohydrates to proteins, causing poorer nitrogen utilization efficiency. Altogether, these results suggest that the reductions in animal growth induced by overgrazing are associated with liver proteomic changes, especially the proteins involved in nitrogen compounds metabolism and immunity. CONCLUSIONS This provides new information that can be used for nutritional supplementation to improve the growth performance of sheep in an overgrazing condition.

中文翻译：

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过度放牧导致绵羊肝蛋白组（Ovis aries）发生改变：基于iTRAQ的定量蛋白质组学分析。

背景技术由于过度放牧，内蒙古草原的退化已导致生态系统破坏以及绵羊生产的大量减少。过度放牧极大地降低了绵羊的生长性能，每年引发大量的经济损失。肝脏是重要的器官，在多种功能（例如营养代谢，免疫力和其他功能）中具有非常重要的作用，而这些功能与动物的生长密切相关。然而，据我们所知，尚无详尽的研究评估过度放牧对绵羊肝脏代谢的适应性。这些作用的分子机制尚不清楚。方法在本研究中，我们的小组应用等压标记进行基于相对和绝对定量（iTRAQ）的定量蛋白质组分析，以研究因过度放牧而减少营养（12.0羊/公顷）时绵羊肝组织蛋白质谱的变化，目的是表征分子放牧条件下绵羊肝脏代谢适应的机制 结果由于过度放牧，绵羊的体重日增重大大降低。总体而言，轻度放牧组和过度放牧组之间在肝组织中发现有41种蛋白质差异丰富。鉴定出的大多数差异表达蛋白质都参与蛋白质代谢，转录和翻译调节以及免疫反应。特别是，参与蛋白质代谢功能的犬尿尿素酶（KYNU）和HAL（组氨酸氨裂合酶）的丰度变化，以及血清尿素氮（BUN）和葡萄糖（GLU）的变化，提示过度放牧会触发能量转移从碳水化合物到蛋白质的资源不足，导致氮利用效率低下。总之，这些结果表明，过度放牧引起的动物生长减少与肝脏蛋白质组学变化有关，尤其是与氮化合物代谢和免疫有关的蛋白质。结论这提供了可用于营养补充的新信息，以改善过度放牧条件下绵羊的生长性能。结合血清尿素氮（BUN）和葡萄糖（GLU）的水平变化，表明过度放牧触发了能源资源从碳水化合物到蛋白质的转移，从而导致氮利用效率降低。总之，这些结果表明，过度放牧引起的动物生长减少与肝脏蛋白质组学变化有关，尤其是与氮化合物代谢和免疫有关的蛋白质。结论这提供了可用于营养补充的新信息，以改善过度放牧条件下绵羊的生长性能。结合血清尿素氮（BUN）和葡萄糖（GLU）的水平变化，表明过度放牧触发了能源资源从碳水化合物到蛋白质的转移，从而导致氮利用效率降低。总之，这些结果表明，过度放牧引起的动物生长减少与肝脏蛋白质组学变化有关，尤其是与氮化合物代谢和免疫有关的蛋白质。结论这提供了可用于营养补充的新信息，以改善过度放牧条件下绵羊的生长性能。这些结果表明，过度放牧引起的动物生长减少与肝脏蛋白质组学变化有关，尤其是与氮化合物代谢和免疫有关的蛋白质。结论这提供了可用于营养补充的新信息，以改善过度放牧条件下绵羊的生长性能。这些结果表明，过度放牧引起的动物生长减少与肝脏蛋白质组学变化有关，尤其是与氮化合物代谢和免疫有关的蛋白质。结论这提供了可用于营养补充的新信息，以改善过度放牧条件下绵羊的生长性能。