Departament Biologia Cel·lular, Fisiologia i Immunologia, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal 643, E-08028 Barcelona, Spain.
Departament Biologia Cel·lular, Fisiologia i Immunologia, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal 643, E-08028 Barcelona, Spain.
Comp Biochem Physiol B Biochem Mol Biol. 2019 Oct;236:110311. doi: 10.1016/j.cbpb.2019.110311. Epub 2019 Jul 4.
Seasonal variations in water temperature are a natural stressor of temperate fish that affect growth performance and metabolism globally. Gilthead sea bream is one of the most economically interesting species in the Mediterranean; but its liver metabolism is affected by the cold season. However, the effects of cold on protein turnover mechanisms have hardly been studied. Here, we study the relationship between liver oxidative status and protein homeostasis pathways during a 50-day low temperature period at 14 °C, and subsequent recovery at two times: 7 days (early recovery) and 30 days (late recovery). Liver redox status was determined by measuring oxidised lipids and proteins, the glutathione redox cycle and major antioxidant enzymes activities. Protein turnover was analysed via liver protein expression of HSP70 and HSP90; proteasome 26S subunits and polyubiquitination, as markers of the ubiquitin-proteasome system (UPS); and cathepsin D, as a lysosomal protease. Low temperature exposure depressed antioxidant enzyme activities, affecting the glutathione redox cycle and reducing total glutathione levels. Both the UPS and lysosomal pathways were also depressed and consequently, oxidised protein accumulated in liver. Interestingly, both protein oxidation and polyubiquitination tagging depended on protein molecular weight. Despite all these alterations, temperature recovery reverted most consequences of the cold at different rates: with delayed recovery of total glutathione levels and oxidised protein degradation with respect to enzyme activities recovery. All these findings demonstrate that protein liver homeostasis is compromised after chronic cold exposure and could be the cause of liver affectations reported in aquaculture of temperate fish.
水温的季节性变化是影响全球温带鱼类生长性能和新陈代谢的自然应激因素。金头鲷是地中海最具经济价值的物种之一；但其肝脏代谢会受到寒冷季节的影响。然而，低温对蛋白质周转机制的影响几乎没有被研究过。在这里，我们研究了在 14°C 的低温下持续 50 天，以及随后在两个时间点（7 天[早期恢复]和 30 天[晚期恢复]）进行恢复期间，肝脏氧化状态与蛋白质稳态途径之间的关系。通过测量氧化脂质和蛋白质、谷胱甘肽氧化还原循环和主要抗氧化酶活性来确定肝脏氧化状态。通过肝脏 HSP70 和 HSP90 的蛋白表达、蛋白酶体 26S 亚基和多泛素化作为泛素蛋白酶体系统 (UPS) 的标志物以及组织蛋白酶 D 作为溶酶体蛋白酶来分析蛋白质周转。低温暴露会降低抗氧化酶的活性，从而影响谷胱甘肽氧化还原循环并降低总谷胱甘肽水平。UPS 和溶酶体途径也受到抑制，因此，肝脏中积累了氧化蛋白。有趣的是，蛋白质氧化和多泛素化标记都依赖于蛋白质的分子量。尽管发生了所有这些变化，但温度恢复以不同的速度逆转了低温的大部分后果：总谷胱甘肽水平和氧化蛋白降解的恢复滞后于酶活性的恢复。所有这些发现表明，慢性冷暴露后肝脏蛋白质稳态受到损害，这可能是温带鱼类水产养殖中肝脏损伤的原因。
