College of Life Science, Henan Normal University, No. 46 Jianshe Road, Xinxiang 453007, PR China.
College of Fisheries, Henan Normal University, No. 46 Jianshe Road, Xinxiang 453007, PR China.
Comp Biochem Physiol B Biochem Mol Biol. 2024 Jan;269:110898. doi: 10.1016/j.cbpb.2023.110898. Epub 2023 Sep 4.
It is widely acknowledged that glucose serves as the primary energy source for organisms. However, fish exhibit persistent postprandial hyperglycemia and are thought to have low glucose tolerance. Glycolysis serves as the ubiquitous pathway for glucose catabolism, with phosphofructokinase (PFK) acting as a crucial rate-limiting enzyme in this process and playing an indispensable role. PFK is classified into three isoforms based on their major expression sites, i.e., PFKM (skeletal muscle type), PFKL (liver type) and PFKP (platelet type). In this study, grass carp (Ctenopharyngodon idella) was used as animal model and the open reading frame (ORF) sequences of six PFK genetic isoforms of grass carp were cloned. Real-time PCR was used to detect its tissue distribution, and expression changes in oral glucose tolerance test (OGTT), insulin and glucagon injection experiments. The results showed that the ORF of pfkla, pfklb, pfkma, pfkmb, pfkpa and pfkpb genes was 2343, 2340, 2355, 2331, 2364 and 2349 bp in length, respectively. The results of tissue distribution showed that pfkla and pfklb, homologous to mammalian pfkl, exhibited low expression levels in the liver of grass carp, but were expressed at the highest level in the brain. Muscle-type pfkma and pfkmb mRNA were found to be highly expressed in both red and white muscle, with pfkmb also exhibiting high expression levels in the heart, while platelet type pfkpa and pfkpb showed high mRNA abundances in the brain and heart. Oral glucose administration stimulated pfkma and pfkmb mRNA expression in the red muscle, and up-regulated pfklb mRNA levels in the liver at 3 h post treatment, but it suppressed liver-type and platelet-type PFK genes expression in the brain. The expression of pfkmb in white muscle and pfkmb and pfkpb in heart were promoted by insulin, whereas the expression of pfkla and pfkpb in the brain, pfkma and pfkmb in the red muscle, pfkma in the white muscle, and pfklb in the liver was suppressed by insulin. As for glucagon, it inhibited pfkma and pfkmb mRNA expression in the red muscle, as well as pfklb in the liver, but it up-regulated PFK genes expression in most tissues detected, such as brain (pfklb, pfkpa and pfkpb), white muscle (pfkma and pfkmb), liver (pfkla) and heart (pfkmb and pfkpb). Our results suggest that PFK family genes have different or even opposite expression patterns in response to glucose, insulin and glucagon stimulation in various tissues of grass carp, which may contribute to glucose intolerance in fish.
人们普遍认为葡萄糖是生物体的主要能量来源。然而，鱼类表现出持续的餐后高血糖，被认为葡萄糖耐量低。糖酵解是葡萄糖分解代谢的普遍途径，磷酸果糖激酶（PFK）作为该过程中的关键限速酶，起着不可或缺的作用。PFK 根据其主要表达部位分为三种同工酶，即 PFKM（骨骼肌型）、PFKL（肝型）和 PFKP（血小板型）。本研究以草鱼（Ctenopharyngodon idella）为动物模型，克隆了草鱼六种 PFK 遗传同工酶的开放阅读框（ORF）序列。实时 PCR 用于检测其组织分布，并在口服葡萄糖耐量试验（OGTT）、胰岛素和胰高血糖素注射实验中检测其表达变化。结果表明，pfkla、pfklb、pfkma、pfkmb、pfkpa 和 pfkpb 基因的 ORF 分别为 2343、2340、2355、2331、2364 和 2349bp。组织分布结果表明，与哺乳动物 pfkl 同源的 pfkla 和 pfklb 在草鱼肝脏中表达水平较低，但在脑中表达水平最高。肌肉型 pfkma 和 pfkmb mRNA 在红肌和白肌中均高度表达，pfkmb 在心脏中也有高表达水平，而血小板型 pfkpa 和 pfkpb 在大脑和心脏中则表现出高 mRNA 丰度。口服葡萄糖刺激红肌中 pfkma 和 pfkmb mRNA 的表达，并在 3h 处理后上调肝脏中 pfklb mRNA 的水平，但抑制脑内肝型和血小板型 PFK 基因的表达。胰岛素促进白肌中的 pfkmb 和心脏中的 pfkmb 和 pfkpb 的表达，而脑内的 pfkla 和 pfkpb、红肌中的 pfkma 和 pfkmb、白肌中的 pfkma 和肝脏中的 pfklb 的表达则受到胰岛素的抑制。至于胰高血糖素，它抑制红肌中 pfkma 和 pfkmb 的表达以及肝脏中 pfklb 的表达，但它上调了大多数检测到的组织中 PFK 基因的表达，如脑（pfklb、pfkpa 和 pfkpb）、白肌（pfkma 和 pfkmb）、肝脏（pfkla）和心脏（pfkmb 和 pfkpb）。我们的结果表明，PFK 家族基因在草鱼各组织对葡萄糖、胰岛素和胰高血糖素刺激的反应中具有不同的甚至相反的表达模式，这可能导致鱼类的葡萄糖耐量降低。
