Storey Janet M, Li Zhenhong, Storey Kenneth B
Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, K1S 5B6, Canada.
Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, K1S 5B6, Canada.
Cryobiology. 2023 Mar;110:79-85. doi: 10.1016/j.cryobiol.2022.11.242. Epub 2022 Nov 26.
The wood frog, Rana sylvatica (aka Lithobates sylvaticus) is the main model for studies of natural freeze tolerance among amphibians living in seasonally cold climates. During freezing, ∼65% of total body water can be converted to extracellular ice and this imposes both dehydration and hypoxia/anoxia stresses on cells. The current study analyzed the responses of the alpha subunit of the hypoxia-inducible transcription factor (HIF-1), a crucial oxygen-sensitive regulator of gene expression, to freezing, anoxia or dehydration stresses, examining six tissues of wood frogs (liver, skeletal muscle, brain, heart, kidney, skin). RT-PCR revealed a rapid elevation hif-1α transcript levels within 2 h of freeze initiation in both liver and brain and elevated levels of both mRNA and protein in liver and muscle after 24 h frozen. However, both transcript and protein levels reverted to control values after thawing except for HIF-1 protein in liver that dropped to ∼60% of control. Independent exposures of wood frogs to anoxia or dehydration stresses (two components of freezing) also triggered upregulation of hif-1α transcripts and/or HIF-1α protein in liver and kidney with variable responses in other tissues. The results show active modulation of HIF-1 in response to freezing, anoxia and dehydration stresses and implicate this transcription factor as a contributor to the regulation of metabolic adaptations needed for long term survival of wood frogs in the ischemic frozen state.
林蛙（Rana sylvatica，又名Lithobates sylvaticus）是研究生活在季节性寒冷气候中的两栖动物自然耐冻性的主要模型。在冷冻过程中，约65%的全身水分可转化为细胞外冰，这会给细胞带来脱水和缺氧/无氧应激。本研究分析了缺氧诱导转录因子（HIF-1）的α亚基（一种关键的氧敏感基因表达调节因子）对冷冻、缺氧或脱水应激的反应，检测了林蛙的六个组织（肝脏、骨骼肌、脑、心脏、肾脏、皮肤）。逆转录聚合酶链反应（RT-PCR）显示，在肝脏和脑中，冷冻开始后2小时内hif-1α转录水平迅速升高，冷冻24小时后肝脏和肌肉中的mRNA和蛋白质水平均升高。然而，解冻后转录本和蛋白质水平均恢复到对照值，但肝脏中的HIF-1蛋白降至对照值的约60%。将林蛙单独暴露于缺氧或脱水应激（冷冻的两个组成部分）也会引发肝脏和肾脏中hif-1α转录本和/或HIF-1α蛋白的上调，其他组织的反应各不相同。结果表明，HIF-1在冷冻、缺氧和脱水应激反应中受到积极调节，表明该转录因子有助于调节林蛙在缺血冷冻状态下长期生存所需的代谢适应。
