Many animals lower their metabolic rate in response to low temperatures and scarcity of food in the winter in phenomena called hibernation or overwintering. Living at high altitude on the Tibetan Plateau where winters are very cold, the frog Nanorana parkeri, survives in one of the most hostile environments on Earth but, to date, relatively little is known about the biochemical and physiological adjustments for overwintering by this species. The present study profiled changes in plasma metabolites of N. parkeri between winter and summer using UHPLC-QE-MS non-target metabolomics in order to explore metabolic adaptations that support winter survival. The analysis showed that, in total, 11 metabolites accumulated and 95 were reduced in overwintering frogs compared with summer-active animals. Metabolites that increased included some that may have antioxidant functions (canthaxanthin, galactinol), act as a metabolic inhibitor (mono-ethylhexylphthalate), or accumulate as a product of anaerobic metabolism (lactate). Most other metabolites in plasma showed reduced levels in winter and were generally involved in energy metabolism including 11 amino acids (proline, isoleucine, leucine, valine, phenylalanine, tyrosine, arginine, tryptophan, methionine, threonine and histidine) and 4 carbohydrates (glucose, citrate, succinate, and malate). Pathway analysis indicated that aminoacyl-tRNA biosynthesis, phenylalanine, tyrosine and tryptophan biosynthesis, and nitrogen metabolism were potentially the most prominently altered pathways in overwintering frogs. Changes to these pathways are likely due to fasting and global metabolic depression in overwintering frogs. Concentrations of glucose and urea, commonly used as cryoprotectants by amphibians that winter on land, were significantly reduced during underwater hibernation in N. parkeri. In conclusion, winter survival of the high-altitude frog, N. parkeri was accompanied by substantial changes in metabolomic profiles and this study provides valuable information towards understanding the special adaptive mechanisms of N. parkeri to winter stresses.

中文翻译：

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越冬藏蛙Naorana parkeri血浆对极端环境的代谢反应：代谢组学综合分析

许多动物在冬季因低温和食物短缺而降低代谢率，这种现象称为冬眠或越冬。生活在冬季非常寒冷的青藏高原高海拔地区，青蛙 Nanorana parkeri 在地球上最恶劣的环境之一中生存，但迄今为止，对该物种越冬的生化和生理调整知之甚少。本研究使用 UHPLC-QE-MS 非目标代谢组学分析了冬季和夏季之间 N. parkeri 血浆代谢物的变化，以探索支持冬季生存的代谢适应性。分析表明，与夏季活跃的动物相比，越冬青蛙总共积累了 11 种代谢物，减少了 95 种代谢物。增加的代谢物包括一些可能具有抗氧化功能（角黄素、半乳糖苷）、作为代谢抑制剂（邻苯二甲酸单乙基己酯）或作为厌氧代谢产物（乳酸）积累的代谢物。血浆中的大多数其他代谢物在冬季显示水平降低，并且通常参与能量代谢，包括 11 种氨基酸（脯氨酸、异亮氨酸、亮氨酸、缬氨酸、苯丙氨酸、酪氨酸、精氨酸、色氨酸、蛋氨酸、苏氨酸和组氨酸）和 4 种碳水化合物（葡萄糖、柠檬酸盐、琥珀酸盐和苹果酸盐）。通路分析表明，氨酰-tRNA 生物合成、苯丙氨酸、酪氨酸和色氨酸生物合成以及氮代谢可能是越冬蛙最显着改变的通路。这些途径的变化可能是由于越冬青蛙的禁食和整体代谢抑制。在陆地上越冬的两栖动物通常用作冷冻保护剂的葡萄糖和尿素的浓度在 N. parkeri 的水下冬眠期间显着降低。总之，高海拔青蛙 N. parkeri 的冬​​季生存伴随着代谢组学的重大变化，这项研究为了解 N. parkeri 对冬季压力的特殊适应机制提供了宝贵的信息。