Hypoxia tolerance measurements in Fundulus heteroclitus and Fundulus majalis

The current study evaluated two closely related, killifish species (Fundulus heteroclitus, Fundulus majalis) to evaluate responses to acute moderate and acute severe hypoxia. Routine metabolic rate and loss of equilibrium were assessed, followed by analysis in skeletal muscle of markers of oxidative damage to proteins (2,4-DNPH) lipids (4-HNE), and DNA (8-OHdG), hypoxia signaling (HIF1α, HIF2α), cellular energy state (p-AMPK: AMPK), and protein degradation (Ubiquitin, LC3B, Calpain 2, Hsp70). Both species had a similar reduction in metabolic rate at low PO2. However, F. heteroclitus was the more hypoxia-tolerant species based on a lower PO2 at which there was loss of equilibrium, perhaps due in part to a lower oxygen demand at all oxygen tensions. Despite the differences in hypoxia tolerance between the species, skeletal muscle molecular markers were largely insensitive to hypoxia, and there were few differences in responses between the species. Thus, the metabolic depression observed at the whole animal level appears to limit perturbations in skeletal muscle in both species during the hypoxia treatments.

本研究选取两种亲缘关系密切的鳉鱼（Fundulus heteroclitus、Fundulus majalis），探究其对急性中度低氧与急性重度低氧的响应。实验首先测定了两种鱼类的常规代谢率与平衡丧失情况，随后对其骨骼肌组织开展分子标志物分析，检测指标涵盖：蛋白质氧化损伤标志物2,4-二硝基苯肼（2,4-DNPH）、脂质氧化损伤标志物4-羟基壬烯醛（4-HNE）、DNA氧化损伤标志物8-羟基脱氧鸟苷（8-OHdG）、低氧信号通路标志物缺氧诱导因子1α（HIF1α）与缺氧诱导因子2α（HIF2α）、细胞能量状态指标磷酸化腺苷酸活化蛋白激酶与腺苷酸活化蛋白激酶比值（p-AMPK:AMPK），以及蛋白质降解相关标志物泛素（Ubiquitin）、LC3B、钙蛋白酶2（Calpain 2）、热休克蛋白70（Hsp70）。
两种鱼类在低氧分压（PO₂）下的代谢率均出现相似程度的下降。然而，以平衡丧失发生时的氧分压更低为判定依据，Fundulus heteroclitus是低氧耐受性更强的物种，这一差异可能部分源于其在所有氧张力下均具有更低的氧需求。
尽管两种鱼类的低氧耐受性存在显著差异，但骨骼肌的分子标志物对低氧整体上并不敏感，且二者的响应差异极小。由此可见，在整体动物层面观测到的代谢抑制现象，似乎可限制两种鱼类在低氧处理过程中骨骼肌受到的扰动。