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Characterizing the composition, metabolism and physiological functions of the fatty liver in Rana omeimontis tadpoles
Frontiers in Zoology ( IF 2.6 ) Pub Date : 2019-11-14 , DOI: 10.1186/s12983-019-0341-x
Wei Zhu 1 , Meihua Zhang 1, 2 , Liming Chang 1, 2 , Wenbo Zhu 1, 2 , Cheng Li 1 , Feng Xie 1 , Huan Zhang 3 , Tian Zhao 1 , Jianping Jiang 1
Affiliation  

Fat storage is required for the life cycle of many organisms. The primary fat depot for most vertebrates is white adipose tissue. However, in primitive vertebrates (e.g., agnathan group and elasmobranchs), the liver is usually responsible for fat storage. Among the vertebrates, amphibians have a unique status, as their larvae live in the water and exhibit some primitive traits that are similar to fish. Although it has been recognized that adult frogs use their abdominal white adipose tissue as a primary fat depot, how tadpoles store their fat is still inconclusive. The metabolic traits and physiological functions of primitive fat depots may have wide-ranging implications on the pathology of abnormal lipid deposition in mammals and the evolution of fat storage. Rana omeimontis tadpoles used their liver as the primary fat depot. In sufficiently fed tadpoles at stage 30–31, the hepatosomatic index (HSI) reached up to 7%, and triglycerides (TG) accounted for 15% of liver weight. Their liver resembled white adipose tissue in histological morphology, characterized by polygonal hepatocytes filled with fat. Their liver metabolic composition was unique, characterized by the dominance of maltotriose, arachidonic acid and dipeptides in soluble carbohydrates, free fatty acids and amino acids. Hepatic fat was the major metabolic fuel of fasted R. omeimontis tadpoles, which had similar reserve mobilization and allocation patterns as mammals. From a developmental perspective, hepatic fat was important to fuel late metamorphic climax. Interestingly, starvation induced accelerated metamorphosis in tadpoles with high HSI (4.96 ± 0.21%). However, this phenomenon was not observed in tadpoles with low HSI (2.71 ± 0.16%), even though they had similar initial body weight and developmental stage. Hepatic fat abundance was the most prominent difference between the two groups. To the best of our knowledge, this is the first report that liver can be the primary fat depot in vertebrates with higher evolutionary status than bony fish. The unique hepatic histological and metabolic traits likely either guard their liver against lipotoxicity or make their hepatocytes adapt to fat accumulation. This fatty liver could be a primitive counterpart of mammalian white adipose tissue (WAT). In addition, our study showed that the hepatic reserves of tadpoles, especially TG content, may provide body condition signals to modulate metamorphosis.

中文翻译:

表征毛蛙蝌蚪脂肪肝的组成、代谢和生理功能

许多生物体的生命周期都需要脂肪储存。大多数脊椎动物的主要脂肪库是白色脂肪组织。然而,在原始脊椎动物(例如,无颌类和软骨鱼类)中,肝脏通常负责脂肪储存。在脊椎动物中,两栖动物具有独特的地位,它们的幼虫生活在水中,表现出一些与鱼类相似的原始特征。尽管已经认识到成年青蛙使用腹部白色脂肪组织作为主要脂肪库,但蝌蚪如何储存脂肪仍然没有定论。原始脂肪库的代谢特征和生理功能可能对哺乳动物异常脂质沉积的病理学和脂肪储存的进化具有广泛的影响。Rana omeimontis 蝌蚪使用它们的肝脏作为主要的脂肪库。在 30-31 阶段喂食充足的蝌蚪中,肝体指数 (HSI) 高达 7%,甘油三酯 (TG) 占肝脏重量的 15%。他们的肝脏在组织学形态上类似于白色脂肪组织,其特征是充满脂肪的多边形肝细胞。他们的肝脏代谢组成是独特的,其特点是麦芽三糖、花生四烯酸和二肽在可溶性碳水化合物、游离脂肪酸和氨基酸中占主导地位。肝脂肪是禁食的 R. omeimontis 蝌蚪的主要代谢燃料,其储备动员和分配模式与哺乳动物相似。从发育的角度来看,肝脏脂肪对于推动晚期变质高潮很重要。有趣的是,饥饿导致高 HSI (4.96 ± 0.21%) 的蝌蚪加速变态。然而,这种现象在低 HSI (2.71 ± 0.16%) 的蝌蚪中没有观察到,尽管它们具有相似的初始体重和发育阶段。肝脂肪丰度是两组之间最显着的差异。据我们所知,这是第一次报告肝脏可以成为脊椎动物的主要脂肪库,其进化状态高于硬骨鱼。独特的肝脏组织学和代谢特征可能保护它们的肝脏免受脂毒性或使它们的肝细胞适应脂肪积累。这种脂肪肝可能是哺乳动物白色脂肪组织 (WAT) 的原始对应物。此外,我们的研究表明,蝌蚪的肝脏储备,尤其是 TG 含量,可能提供身体状况信号来调节变态。即使他们的初始体重和发育阶段相似。肝脂肪丰度是两组之间最显着的差异。据我们所知,这是第一次报告肝脏可以成为脊椎动物的主要脂肪库,其进化状态高于硬骨鱼。独特的肝脏组织学和代谢特征可能保护它们的肝脏免受脂毒性或使它们的肝细胞适应脂肪积累。这种脂肪肝可能是哺乳动物白色脂肪组织 (WAT) 的原始对应物。此外,我们的研究表明,蝌蚪的肝脏储备,尤其是 TG 含量,可能提供身体状况信号来调节变态。即使他们的初始体重和发育阶段相似。肝脂肪丰度是两组之间最显着的差异。据我们所知,这是第一次报告肝脏可以成为脊椎动物的主要脂肪库,其进化状态高于硬骨鱼。独特的肝脏组织学和代谢特征可能保护它们的肝脏免受脂毒性或使它们的肝细胞适应脂肪积累。这种脂肪肝可能是哺乳动物白色脂肪组织 (WAT) 的原始对应物。此外,我们的研究表明,蝌蚪的肝脏储备,尤其是 TG 含量,可能提供身体状况信号来调节变态。据我们所知,这是第一次报告肝脏可以成为脊椎动物的主要脂肪库,其进化状态高于硬骨鱼。独特的肝脏组织学和代谢特征可能保护它们的肝脏免受脂毒性或使它们的肝细胞适应脂肪积累。这种脂肪肝可能是哺乳动物白色脂肪组织 (WAT) 的原始对应物。此外,我们的研究表明,蝌蚪的肝脏储备,尤其是 TG 含量,可能提供身体状况信号来调节变态。据我们所知,这是第一次报告肝脏可以成为脊椎动物的主要脂肪库,其进化状态高于硬骨鱼。独特的肝脏组织学和代谢特征可能保护它们的肝脏免受脂毒性或使它们的肝细胞适应脂肪积累。这种脂肪肝可能是哺乳动物白色脂肪组织 (WAT) 的原始对应物。此外,我们的研究表明,蝌蚪的肝脏储备,尤其是 TG 含量,可能提供身体状况信号来调节变态。这种脂肪肝可能是哺乳动物白色脂肪组织 (WAT) 的原始对应物。此外,我们的研究表明,蝌蚪的肝脏储备,尤其是 TG 含量,可能提供身体状况信号来调节变态。这种脂肪肝可能是哺乳动物白色脂肪组织 (WAT) 的原始对应物。此外,我们的研究表明,蝌蚪的肝脏储备,尤其是 TG 含量,可能提供身体状况信号来调节变态。
更新日期:2020-04-22
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