Zhang Yichi, Al-Attar Rasha, Storey Kenneth B
Institute of Biochemistry, Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada.
Institute of Biochemistry, Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada.
Cryobiology. 2017 Dec;79:43-49. doi: 10.1016/j.cryobiol.2017.09.003. Epub 2017 Sep 22.
Rana sylvatica, known as the wood frog, can survive extremely cold temperatures during winter by undergoing full-body freezing, where it tolerates freezing of 65-70% of its total body water. During freezing, cellular dehydration decreases damage to the cell by preventing ice crystallization. Challenged with many stresses, these animals are forced to develop physiological adaptations to osmoregulation and osmoprotection that are necessary to ensure their survival. The purpose of this study was to elucidate a potential mechanism by which the transcription factor, NFAT5, regulates the expression of three osmoregulatory proteins (aldose reductase, SMIT, and BGT-1). These three proteins control cellular concentrations of the organic osmolytes: betaine (BGT-1), myo-inositol (SMIT), and sorbitol (aldose reductase). We studied this mechanism during the freeze-thaw stress in R. sylvatica liver, kidney, and skeletal muscle. Protein expression of BGT-1, SMIT, aldose reductase, and NFAT5 were examined using immunoblotting. We identified that the NFAT5 pathway facilitated osmoregulation in a tissue-specific manner during freezing. In skeletal muscle, we demonstrated that NFAT5 upregulation in thawing led to increases in the protein levels of BGT-1. In liver, NFAT5 was upregulated during freezing, along with aldose reductase. Furthermore, neither of these patterns of expression were observed in kidney as none of these four proteins showed differential expression during freezing or thawing. Therefore, the NFAT5 osmoregulatory pathway appears to be tissue-specific. Our novel findings on a mechanism of osmoregulation in R. sylvatica highlight the importance of studying naturally stress-tolerant animals to identify novel pro-survival pathways.
林蛙（Rana sylvatica），也被称为木蛙，在冬季能够通过全身冻结来抵御极低的温度，在此过程中它能耐受全身65% - 70%的水分冻结。在冻结过程中，细胞脱水通过防止冰晶形成来减少对细胞的损伤。面对多种压力，这些动物被迫发展出对渗透调节和渗透保护的生理适应机制，以确保生存。本研究的目的是阐明转录因子NFAT5调节三种渗透调节蛋白（醛糖还原酶、SMIT和BGT - 1）表达的潜在机制。这三种蛋白质控制着细胞内有机渗透溶质的浓度：甜菜碱（BGT - 1）、肌醇（SMIT）和山梨醇（醛糖还原酶）。我们在林蛙肝脏、肾脏和骨骼肌的冻融应激过程中研究了这一机制。使用免疫印迹法检测了BGT - 1、SMIT、醛糖还原酶和NFAT5的蛋白表达。我们发现NFAT5途径在冻结过程中以组织特异性的方式促进渗透调节。在骨骼肌中，我们证明解冻过程中NFAT5的上调导致BGT - 1蛋白水平增加。在肝脏中，NFAT5在冻结过程中与醛糖还原酶一起上调。此外，在肾脏中未观察到这些表达模式，因为这四种蛋白质在冻结或解冻过程中均未显示出差异表达。因此，NFAT5渗透调节途径似乎具有组织特异性。我们关于林蛙渗透调节机制的新发现突出了研究天然耐应激动物以识别新的促生存途径的重要性。
