中国水产科学  2024, Vol. 31 Issue (10): 1141-1150  DOI: 10.12264/JFSC2024-0013
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引用本文 

吉群, 曾霖, 熊逸飞, 王永红, 宋炜. 低盐驯化对急性低盐胁迫下大黄鱼能量代谢和线粒体自噬的影响机制[J]. 中国水产科学, 2024, 31(10): 1141-1150. DOI: 10.12264/JFSC2024-0013.
JI Qun, ZENG Lin, XIONG Yifei, WANG Yonghong, SONG Wei. Mechanistic studies on the effect of low-salinity acclimation on energy metabolism and mitophagy of Larimichthys crocea under acute low-salinity stress[J]. Journal of Fishery Sciences of China, 2024, 31(10): 1141-1150. DOI: 10.12264/JFSC2024-0013.

基金项目

国家重点研发计划项目(2022YFD2401102);青岛海洋科技中心山东省专项经费项目(2022QNLM30001);中国水产科学研究院基本科研业务费项目(2020TD76).

作者简介

吉群(1998‒),男,硕士,研究方向为海水鱼类生理生态学. E-mail:jq17768222360@163.com

通信作者

通信作者:宋炜,研究员,研究方向为海水养殖. E-mail:songw@ecsf.ac.cn

文章历史

收稿日期:2024-01-16
修改日期:2024-02-06
低盐驯化对急性低盐胁迫下大黄鱼能量代谢和线粒体自噬的影响机制
吉群1,3,曾霖2,熊逸飞1,3,王永红2,宋炜1,3,     
1. 中国水产科学研究院东海水产研究所,上海 200090
2. 蚌埠学院食品与生物工程学院,安徽 蚌埠 233030
3. 上海海洋大学水产与生命学院,上海 201306
摘要:为探究低盐驯化对低盐胁迫下大黄鱼(Larimichthys crocea)能量代谢和线粒体自噬的影响机制,将体重为(53.46±1.47) g大黄鱼幼鱼从自然海水(盐度25)转移到盐度20的水体中驯化7 d后在低盐(盐度12)水体中暴露24 h。结果表明,低盐胁迫增加了活性氧(reactive oxygen species,ROS)和三磷酸腺苷(adenosine triphosphate,ATP)含量,提高了三羧酸循环酶活力和线粒体自噬基因表达水平,表明低盐胁迫增强了大黄鱼有氧代谢和线粒体自噬,但仍遭受氧化损伤。与低盐组相比,低盐驯化+低盐组提高了ATP含量、三羧酸循环酶活力和线粒体自噬基因表达水平,降低了ROS含量,表明低盐驯化通过改善低盐胁迫下大黄鱼的能量代谢和线粒体自噬来降低氧化损伤。在低盐胁迫过程中,腺苷酸活化蛋白激酶[adenosine 5ʹ-monophosphate (AMP)-activated protein kinase,AMPK]与三羧酸循环酶和脂肪酸β氧化酶活力成正相关,与脂肪合成酸成负相关,表明大黄鱼通过AMPK来促进产能代谢,抑制耗能代谢,从而改善能量代谢效率。叉头框转录因子O亚型3 (forkhead box class O3,FoxO3)与线粒体自噬基因表达水平呈正相关,表明FoxO3在低盐适应过程中参与了线粒体自噬基因表达的调控。以上结果说明,低盐驯化改善了有氧代谢和线粒体自噬,抑制了脂类合成,从而增强了大黄鱼对低盐胁迫的耐受性。
关键词大黄鱼    低盐驯化    急性低盐胁迫    线粒体自噬    能量代谢    
Mechanistic studies on the effect of low-salinity acclimation on energy metabolism and mitophagy of Larimichthys crocea under acute low-salinity stress
JI Qun1,3,ZENG Lin2,XIONG Yifei1,3,WANG Yonghong2,SONG Wei,1,3    
1. East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai 200090, China
2. School of Food and Biological Engineering, Bengbu University, Bengbu 233030, China
3. College of Fisheries and Life Sciences, Shanghai Ocean University, Shanghai 201306, China
Abstract:The large yellow croaker (Larimichthys crocea) is one of the most economically important marine fish species in China. Reducing water salinity can effectively prevent white spot disease, but it can also cause low-salinity stress and damage to fish. Low-salinity acclimation can improve the body's tolerance to low salinity; therefore, it is necessary to explore the specific physiological mechanisms of low-salinity acclimation in fish under low-salinity stress. This study aimed to investigate the effects of low-salinity acclimation on energy metabolism and mitophagy in the large yellow croaker under low-salinity stress. Juvenile large yellow croakers with a body weight of (53.46±1.47) g were transferred from natural seawater (salinity 25) to water with a salinity of 20 and were cultured for 7 d and then exposed to low-salinity (salinity 12) water for 24 h. The results showed that low-salinity stress increased reactive oxygen species (ROS), adenosine triphosphate (ATP) content, tricarboxylic acid (TCA) cycle enzyme activities, and mitophagy gene expression levels, indicating that L. crocea improved aerobic metabolism and mitophagy under low-salinity stress but still suffered from oxidative damage. Compared with the low-salinity group, the low-salinity acclimation with low-salinity group showed increased ATP content, TCA enzyme activities, and mitophagy gene expression levels but reduced ROS content, indicating that low-salinity acclimation reduced oxidative damage by improving energy metabolism and mitophagy in large yellow croaker under low-salinity stress. During low-salinity stress, adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activity was positively correlated with TCA and fatty acid β oxidation enzyme activities and negatively correlated with fatty acid synthesis enzyme activity, indicating that AMPK promoted energy-yielding metabolism and inhibited energy-consumptive metabolism in L. crocea, thereby improving energy generation efficiency. Forkhead box class O3 (FoxO3) mRNA levels were positively correlated with the expression levels of mitophagy genes, indicating that FoxO3 participates in the regulation of mitophagy gene expression during low-salinity adaptation. In summary, low-salinity acclimation improved aerobic metabolism and mitophagy, inhibited lipid synthesis, and enhanced the tolerance of L. crocea to low-salinity stress.
Key words Larimichthys crocea     low-salinity acclimation    acute low-salinity stress    mitophagy    energy metabolism    

大黄鱼(Larimichthys crocea)自从1986年突破其人工繁育以来,其养殖业迅速发展,现已发展成为了单一海水养殖鱼类产量最大的品种,2022年全国产量达到25.77万t[1-2]。为了抵御台风等极端气候的影响,大黄鱼养殖水域主要分布在避风条件较好的内湾,而且渔民通常会增加养殖网箱数量,并采用高密度养殖方式来增加单位养殖面积的经济效率,这易导致养殖区域水流不畅,水体污染严重,病虫害频发,尤其是寄生虫病如刺激隐核虫(Cryptocaryon irritans)(俗称“白点病”)[3]。研究表明,降低水体盐度能破坏寄生虫生长繁殖的环境,从而有效预防白点病[4]。目前,大黄鱼工厂化半咸水养殖、深远海养殖工船模式(停泊到低盐海区或向养殖仓内输入淡水来防治“白点病”)和接力养殖(由高盐水域向低盐水域转移)等新型的健康养殖模式正在研发[5-6]。另外,适当降低盐度可以降低鱼类渗透压调节所消耗的能量,节约的能量可以促进鱼类的生长[7]。降低盐度给鱼类带来有利影响的同时也造成了低盐应激。采用何种方式降低水体盐度来减缓低盐胁迫对机体的损伤是大黄鱼新型养殖方式必须面对的问题[8]。在养殖实践中,渔民通常先采用低盐驯化,然后再进一步降低养殖水体的盐度,这与“毒物兴奋效应”原理相吻合,即低剂量胁迫经历可以改善机体对随后相同或不同高剂量胁迫因子的耐受性[9]。低盐驯化能否抑制低盐胁迫诱导的氧化损伤?其具体的作用机制是什么?尚未见相关报道,值得深入探究。

水体盐度变化干扰细胞的渗透压平衡。机体需要调节相关的酶活性和基因表达来促使细胞的渗透压重新平衡,这一过程需要消耗大量的能量[10]。这些能量主要由3大营养物质(碳水化合物、脂肪和蛋白质)通过新陈代谢提供。碳水化合物在丙酮酸激酶(pyruvate kinase, PK)的催化作用下形成丙酮酸[11]。在有氧条件下,丙酮酸进入三羧酸循环,通过线粒体电子传递链彻底氧化,产生大量的三磷酸腺苷(adenosine triphosphate, ATP)。ATP合成酶(ATP synthase, F-ATP)、琥珀酸脱氢酶(succinate dehydrogenase, SDH)以及苹果酸脱氢酶(malate dehydrogenase, MDH)在三羧酸循环中发挥重要的催化作用[12]。在无氧条件下,丙酮酸在乳酸脱氢酶(lactic dehydrogenase, LDH)的作用下生成乳酸,并伴随少量能量产生[13]。在脂类代谢中,乙酰辅酶A羧化酶(acetyl-CoA carboxylase, ACC)和肉碱棕榈酰转移酶-1 (carnitine palmitoyl transterase-1, CPT-1)分别是脂肪酸生物合成和脂肪酸β氧化的关键酶。脂肪酸β氧化产物可以通过三羧酸循环为机体提供能量[14]。腺苷酸活化蛋白激酶[adenosine 5ʹ-monophosphate (AMP)-activated protein kinase, AMPK],被称为“细胞能量感受器”,它能通过调节物质代谢来维持细胞能量平衡,增强机体的胁迫耐受性[15]。目前,有关低盐驯化对低盐胁迫下能量代谢影响的研究比较匮乏。

线粒体是活性氧(reactive oxygen species, ROS)产生和能量代谢的主要场所。维持线粒体稳态有助于提高机体的胁迫耐受性。线粒体自噬能特异性识别并清除含有大量ROS的受损线粒体及其内含物,从而维持线粒体稳态[16]。微管相关蛋白轻链3 (microtubule-associated protein light chain 3, LC3α)是线粒体自噬标志物,PTEN诱导的假定激酶1 (PTEN induced putative kinase 1, PINK1)、PARKIN编码蛋白(Parkin)和线粒体融合蛋白2 (mitofusin 2, Mfn2)在线粒体自噬过程中发挥重要作用,这些基因的表达主要受转录因子叉头框转录因子O亚型3 (forkhead box class O3, FoxO3)的调控[17-18]。目前,有关低盐胁迫对鱼类线粒体自噬的作用机制研究较为缺乏。

为了探索鱼类对盐度胁迫的响应机制,本课题组采用转录组学技术研究了低盐驯化对低盐胁迫下大黄鱼基因表达的影响,发现差异表达基因显著富集在非特异性免疫相关的凋亡、能量代谢和自噬相关信号通路中[19];盐度驯化可以提高大黄鱼抗氧化和非特异性免疫能力来缓解盐度胁迫带来的氧化损伤,从而改善大黄鱼对盐度胁迫的耐受性[20];大黄鱼会通过提高糖类和脂类分解代谢以及线粒体自噬,同时抑制脂类合成代谢来适应盐度胁迫,但高盐和低盐胁迫对其能量代谢和线粒体自噬的影响存在差异[21]。基于上述研究积累,本研究进一步解析低盐驯化对低盐胁迫下大黄鱼能量代谢和线粒体自噬的影响及其作用机制。将大黄鱼从自然海水(盐度25)转移到盐度20的水体中驯化7 d,再转移到盐度12的水体中暴露24 h。测量氧化损伤标志物(ROS)、能量代谢指标(ATP和乳酸含量;PK、LDH、SDH、MDH、F-ATP和AMPK酶活力)和线粒体自噬指标(LC3αParkinPINK1Mfn2FoxO3基因表达水平)。研究结果可为低盐驯化改善大黄鱼对低盐胁迫的耐受性提供理论依据,也为工厂化半咸水养殖、深远海养殖工船模式和接力养殖等低盐养殖方式提供基础资料。

1 材料与方法 1.1 实验设计

240尾实验大黄鱼(53.46±1.47) g来自中国水产科学研究院东海水产研究所福建福鼎研究中心。将实验大黄鱼随机放入12个400 L容积的养殖桶中暂养,每桶20尾。水质参数如下:盐度25.12±0.63、温度(22.54±1.64) ℃、pH 7.42±0.38、溶解氧(7.31±0.36) mg/L、总氨氮为(0.12~0.27) mg/L。暂养2周后正式开始实验。将12个养殖桶分为2组,6个桶养殖桶的水体盐度维持不变(盐度25),剩余6个桶养殖桶的水体盐度由25降至20。暂养和低盐驯化期间,每天投喂商业饲料2次(08:00和16:00),投喂1 h后清除残饵。驯化7 d后,每组中3个养殖桶的盐度维持不变,另外3个养殖桶的盐度以2.5/h的速率从盐度25或20降至盐度12。此时,实验组可分为对照组(C组)、低盐组(L组)、低盐驯化组(A组)和低盐驯化+低盐组(AL组),每组3个平行(图1)。低盐水体由天然海水加入适量的淡水调配而成。低盐胁迫24 h后采集样本,每桶随机抽取4尾鱼,取肝脏样本放置液氮中,用于分子和生化指标分析。

图1  实验组示意图 Fig. 1  Schematic diagram of experimental groups
1.2 生化指标分析

参考Zeng等[3]研究方法,使用PBS盐溶液(碧云天生物技术,中国)对肝脏样本匀浆,取上清液用于后续的生化指标测定。购买商品试剂盒(南京建成生物工程研究所,中国)参照说明书操作测定ROS、ATP和乳酸含量以及PK、LDH、SDH、MDH、F-ATP和AMPK酶活力。采用化学荧光法(吸光值525 nm)测量ROS含量,将C组的值设为1,其余组的值与C组的值进行对比,计算出相对的ROS含量;采用磷钼酸比色法(吸光值636 nm)测定ATP含量;采用比色法测量乳酸含量、LDH、SDH和F-ATP酶活力,测定过程中使用的吸光值分别为530 nm、440 nm、600 nm和340 nm。采用紫外比色法(吸光值340 nm)分析PK和MDH酶活力。购买商品试剂盒(北京索莱宝科技有限公司,中国)采用分光光度法(吸光值660 nm)测量ACC酶活力。使用试剂盒(碧云天生物技术,中国)采用Bradford法测量肝脏的蛋白含量。酶活性以每毫克蛋白中所含的活力单位(U)表示。

购买鱼磷酸化腺苷酸活化蛋白激酶(AMPK) ELISA检测试剂盒(上海酶联生物,BIO)和肉毒碱棕榈酰转移酶1 (CPT-1) ELISA试剂盒(上海酶联生物,BIO)测量AMPK和CPT-1酶活力。具体步骤如下:采取抗体二步夹心法进行酶联免疫吸附实验,两者均在酶标仪450 nm波长下测定吸光度(OD值),通过标准曲线计算酶活力。

1.3 基因表达分析

参考Zeng等[22]方法测定基因表达水平。简而言之,采用TRIzol (碧云天生物技术,中国)提取RNA,采用cDNA第一链合成试剂盒(Fermentas)将RNA逆转录成cDNA,采用SuperReal PreMix Plus (SYBR Green)通过实时荧光定量PCR测定基因表达。参考Zeng等[22]设计实时荧光定量引物(表1)。PCR反应程序为:95 ℃, 15 min; 95 ℃, 15 s; 58 ℃, 30 s; 35个循环。以β-actin为内参基因,采用2−ΔΔCt方法计算基因表达水平[23]。将C组的值设为1,其余组的值与C组的值进行对比,计算出相对表达量。

表1  实时荧光定量PCR引物 Tab. 1  Real-time quantitative PCR primer
1.4 统计分析

数值以平均值±标准差($\bar x \pm {\rm{SD}}$)表示。在统计分析之前,分别用Kolmogorov-Smirnov检验和Bartlett检验进行正态分布和方差同质性分析。然后采用单因素方差分析(one-way ANOVA)和Duncan氏法评估不同处理组之间的差异(P<0.05)。采用Pearson相关性分析检验不同参数之间的相关性。所有统计分析均由SPSS 19.0软件完成。

2 结果与分析 2.1 ROS、ATP和乳酸含量

与C组相比,L组大黄鱼的ROS和ATP含量显著升高,乳酸含量无显著变化;A组大黄鱼的ATP含量显著升高,ROS和乳酸含量无显著变化。与L组相比,AL组大黄鱼的ATP含量显著升高,乳酸含量无显著变化,ROS含量显著降低(图2)。盐度变化会产生大量ROS,低盐驯化可以缓解低盐胁迫诱导的大黄鱼氧化损伤。

图2  盐度胁迫对大黄鱼肝脏ROS、ATP和乳酸含量的影响C、A、L、AL分别代表对照组、低盐驯化组、低盐组和低盐驯化+低盐组. 不同的字母表示各处理组之间存在显著差异(P<0.05).. Fig. 2  Effects of salinity stress on ROS, ATP and lactate contents in the liver of Larimichthys croceaC, A, L and AL represent the control group, low-salinity acclimation group, low-salinity group and low-salinity acclimation+ low-salinity group, respectively. Different letters indicate significant differences among groups (P<0.05).
2.2 糖类代谢酶和AMPK酶活力

与C组相比,L组大黄鱼的PK、SDH、MDH和F-ATP酶活力显著增加,AMPK酶活力无显著变化,LDH酶活力显著降低;A组大黄鱼的SDH、MDH和AMPK酶活力显著增加,PK、LDH和F-ATP酶活力无显著变化。与L组相比,AL组大黄鱼的大部分糖类代谢酶和AMPK酶活力显著升高(图3)。低盐胁迫提高了有氧代谢,降低了无氧代谢,从而提高了能量代谢效率。低盐驯化提高了低盐胁迫下大黄鱼的有氧代谢,糖类代谢为机体提供了更多的能量,从而改善了机体对低盐胁迫的耐受性。

图3  盐度胁迫对大黄鱼肝脏AMPK和糖类代谢酶活力的影响C、A、L、AL分别代表对照组、低盐驯化组、低盐组和低盐驯化+低盐组. 不同的字母表示各处理组之间存在显著差异(P<0.05).. Fig. 3  Effects of salinity stress on AMPK and carbohydrate metabolism enzyme activities in the liver of Larimichthys croceaC, A, L and AL represent the control group, low-salinity acclimation group, low-salinity group and low-salinity acclimation+ low-salinity group, respectively. Different letters indicate significant differences among groups (P<0.05).
2.3 脂类代谢酶活力

与C组相比,L组和A组大黄鱼的CPT-1和ACC酶活力无显著变化。与L组相比,AL组大黄鱼的CPT-1酶活力无显著变化,ACC酶活力显著降低(图4)。低盐胁迫对大黄鱼的脂类代谢不产生影响,而低盐驯化会抑制低盐胁迫下大黄鱼的脂类合成代谢,从而节约能量用于适应低盐胁迫。

图4  盐度胁迫对大黄鱼肝脏脂类代谢酶活力的影响C、A、L、AL分别代表对照组、低盐驯化组、低盐组和低盐驯化+低盐组. 不同的字母表示各处理组之间存在显著差异(P<0.05).. Fig. 4  Effects of salinity stress on lipid metabolism enzyme activities in the liver of Larimichthys croceaC, A, L and AL represent the control group, low-salinity acclimation group, low-salinity group and low-salinity acclimation+ low-salinity group, respectively. Different letters indicate significant differences among groups (P<0.05).
2.4 线粒体自噬基因表达水平

与C组相比,L组大黄鱼的LC3αMfn2基因表达水平显著增加,PINK1ParkinFoxO3基因表达水平无显著差异;A组大黄鱼的线粒体自噬基因表达水平无显著变化。与L组相比,AL组大黄鱼的LC3αParkinFoxO3基因表达水平显著升高,PINK1Mfn2基因表达水平无显著变化(图5)。低盐胁迫会激活大黄鱼线粒体自噬,而低盐驯化会增强低盐胁迫后的大黄鱼线粒体自噬水平。

图5  盐度胁迫对大黄鱼肝脏线粒体自噬基因表达水平的影响C、A、L、AL分别代表对照组、低盐驯化组、低盐组和低盐驯化+低盐组. 不同的字母表示各处理组之间存在显著差异(P<0.05).. Fig. 5  Effects of salinity stress on mitophagy gene expression levels in the liver of Larimichthys croceaC, A, L and AL represent the control group, low-salinity acclimation group, low-salinity group and low-salinity acclimation+ low-salinity group, respectively. Different letters indicate significant differences among groups (P<0.05).
2.5 相关性分析

AMPK酶活力与PK、SDH、MDH、F-ATP和CPT-1酶活力成正相关,与ACC酶活力成负相关 (表2)。FoxO3基因表达水平与LC3αPINK1ParkinMfn2基因表达水平成正相关(表3)。

表2  AMPK与能量代谢酶活力之间的相关性分析 Tab. 2  Pearson's correlation coefficients between AMPK and energy metabolism enzyme activities
表3  FoxO3与线粒体自噬基因表达水平之间的相关性分析 Tab. 3  Pearson's correlation coefficients between FoxO3 and mitophagy mRNA levels
3 讨论

尽管低盐胁迫对鱼类生理功能的影响已有大量报道,但有关低盐驯化对低盐胁迫下鱼类生理功能的影响研究不足。本研究表明,低盐驯化可能通过改善低盐胁迫下鱼类的能量代谢和线粒体自噬来缓解氧化损伤,这为低盐驯化保护鱼类免受低盐胁迫损伤的作用机制提供新见解。

3.1 低盐驯化对低盐胁迫下氧化损伤的影响

研究表明,低盐胁迫会对鱼类产生氧化损伤。与课题组的研究结果相似,即低盐组(L组)的ROS含量显著高于对照组,强调了低盐胁迫对鱼类的负面影响。大黄鱼对环境变化比较敏感[24]。盐度变化会破坏鱼类细胞的氧化还原平衡,导致线粒体膜超极化,诱导大量的ROS产生。过量的ROS会导致蛋白质羰基化、脂质过氧化、核酸突变,甚至死亡[25]。低盐驯化(A组)未对大黄鱼的ROS含量产生影响,表明其具有较强的低盐适应能力。值得注意的是低盐驯化+低盐胁迫组(AL组)大黄鱼产生的ROS含量显著低于低盐组(L组),表明低盐驯化缓解了大黄鱼低盐胁迫诱导的氧化损伤。适中的高温驯化可以提高虹鳟(Oncorhynchus mykiss)对盐度胁迫的耐受性[26]。低氧驯化可以提高大黄鱼对铜胁迫的耐受性[22]。与课题组前期的研究结果一致,都符合“毒物兴奋效应”原理[9]

3.2 低盐驯化对低盐胁迫下能量代谢的影响

鱼类在调节细胞渗透压重新平衡过程中需要消耗大量的能量。低盐胁迫耐受性与机体能量供应密切相关[27-28]。在本实验中,低盐胁迫提高了糖酵解(PK)和三羧酸循环(SDH、MDH和F-ATP)关键酶的活力,降低了无氧代谢(LDH)酶的活力,表明低盐胁迫提高了有氧代谢,降低了无氧代谢,从而提高了能量代谢效率。L组的ATP含量增加证实了上述观点。低盐驯化提高了大黄鱼三羧酸循环关键酶的活力,且AL组的大黄鱼三羧酸循环关键酶活力显著高于L组,表明低盐驯化提高了低盐胁迫下大黄鱼的有氧代谢。在这种情况,糖类代谢能为机体提供更多的能量,从而改善了机体对低盐胁迫的耐受性。脂类是机体的主要贮能物质[29]。低盐胁迫对CPT-1和ACC酶活力不产生影响,表明低盐胁迫对大黄鱼的脂类代谢不产生影响。糖类能为机体快速提供血糖,是鱼类急性胁迫适应过程中的主要能量来源。脂类代谢可为鱼类慢性胁迫适应提供大量能量。鱼类在24 h低盐胁迫适应过程中所需要的能量主要由糖类代谢提供。海鲈(Lateolabrax maculatus)在低盐胁迫适应的初始阶段所需的能量主要由糖类代谢提供,随着胁迫时间的延长,转变成由脂类代谢提供[30]。尽管低盐驯化对CPT-1和ACC酶的活力不产生影响,但AL组的ACC酶活力显著低于L组。其原因可能是低盐驯化抑制了低盐胁迫下大黄鱼的脂类合成代谢,可以节约能量用于低盐胁迫适应。

3.3 低盐驯化对低盐胁迫下线粒体自噬的影响

线粒体自噬是一种自主降解的适应机制,能够识别并清除受损的线粒体及其内含物,从而降低ROS含量,提高机体对胁迫的耐受性[31]PINK1/Parkin是线粒体自噬的主要信号通路之一,Mfn2PINK1/Parkin泛素化修饰而激活,参与细胞的增殖和凋亡调节,LC3α是线粒体自噬的生物标志物[17,32]。在本实验中,低盐胁迫提高了线粒体自噬基因(LC3αPINK1ParkinMfn2)的表达水平,表明低盐胁迫激活了线粒体自噬。由于低盐胁迫诱导机体产生大量的ROS,损伤了线粒体,鱼类可以通过线粒体自噬途径将受损的线粒体用于物质能量循环,在清除ROS的同时节约了物质和能量,从而增加了机体对低盐胁迫的适应性。尽管低盐驯化对线粒体自噬基因的表达不产生影响,但AL组的线粒体自噬基因表达水平显著高于L组,表明低盐驯化提高了低盐胁迫下大黄鱼的线粒体自噬。

3.4 能量代谢和线粒体自噬的调控机制

AMPK能感知细胞能量变化,通过调节物质代谢来维持机体的能量平衡,被称为“细能量指示器”[33]。AMPK通过提高产能代谢,抑制耗能代谢来为机体提供更多的能量,从而改善机体对胁迫的耐受能力[34]。在本实验中,低盐胁迫提高了大黄鱼肝脏AMPK酶活力,表明低盐激活了AMPK表达。这与盐度和低温胁迫均可提高大鳞鲆、大黄鱼AMPK表达水平[15,35]的研究结果一致。AL组的大黄鱼AMPK酶活力显著高于L组,表明低盐驯化提高了低盐胁迫下大黄鱼AMPK表达。AMPK酶活力与PK、SDH、MDH、F-ATP和CPT-1酶活力成正相关,表明大黄鱼可以通过激活AMPK来促进三羧酸循环和脂肪酸β氧化,从而获得充足的能量。AMPK酶活力与ACC酶活力成负相关,表明大黄鱼可以通过激活AMPK来抑制脂肪酸合成,从而降低能量消耗。FoxO3在调节线粒体自噬基因表达方面具有重要作用[18]。在本实验中,FoxO3LC3αParkinPINK1Mfn2基因表达水平成呈正相关,表明鱼类可以通过FoxO3调控线粒体自噬基因的表达来应对低盐胁迫。与研究结果[22]相似。

4 小结

鱼类在低盐胁迫适应过程中增强了有氧代谢和线粒体自噬,但仍遭受低盐胁迫诱导的氧化损伤。低盐驯化改善了有氧代谢和线粒体自噬,抑制了脂类合成,从而增强了鱼类对低盐胁迫的耐受性。本文强调在评估低盐胁迫对鱼类生理功能影响时,需要考虑鱼类的低盐驯化史。

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