College of Food Science and Technology, Hunan Agricultural University, Changsha, 410128, Hunan, China.
Hunan Provincial Key Laboratory of Nutrition and Quality Control of Aquatic Animals, Department of Biological and Chemical Engineering, Changsha University, Changsha, 410022, China.
Mar Biotechnol (NY). 2024 Feb;26(1):74-91. doi: 10.1007/s10126-023-10278-5. Epub 2023 Dec 28.
The study aimed to compare the effects of crystalline L-lysine and L-glutamate (CAA), Lys-Glu dipeptide (KE) on the growth and muscle development of grass carp (Ctenopharyngodon idellus), and related molecular mechanisms. Five experimental diets (CR, 0.5% CAA, 1.5% CAA, 0.5% KE, 1.5% KE) containing Lys and Glu as free (Lys and Glu, CAA) dipeptide (Lys-Glu, KE) forms were prepared, respectively. A total of 450 juvenile grass carp with an initial weight of 10.69 ± 0.07 g were randomly assigned to 15 cages, and 5 treatments with 3 replicates of 30 fish each for 61 days of feeding. The results showed that the group of 0.5% KE exhibited the best growth performances according to the indicator's weight gain rate (WGR) and specific growth rate (SGR), although no statistically significant occurred among all groups; diet supplemented with 0.5% CAA significantly elevated the condition factor (CF) and viscerasomatic index (VSI) of juvenile grass carp. Diet supplemented with different Lys and Glu co-forms at different levels promoted the muscle amino acid content compared with those of CR group. Comparing with the CR group and other groups, the hardness of 0.5% CAA group significantly increased, and the springiness of 0.5% KE group excelled. Both the muscle fiber diameter and density of 0.5% KE group showed significant difference with those of the CR group, and a negative correlation between them was also observed. To uncover the related molecular mechanism of the differences caused by the different co-forms of Lys and Glu, the effect of different diets on the expressions of protein absorption, muscle quality, and antioxidation-related genes was analyzed. The results suggested that comparing with those of CR group, the dipeptide KE inhibited the expressions of genes associated with protein metabolism, such as AKT, S6K1, and FoxO1a but promoted PCNA expression, while the free style of CAA would improve the FoxO1a expression. Additionally, the muscle development-related genes (MyoD, MyOG, and Myf5) were significantly boosted in CAA co-form groups, and the expressions of fMYHCs were blocked but fMYHCs30 significantly promoted in 0.5% KE group. Finally, the effect of different co-forms of Lys and Glu on muscle antioxidant was examined. The 0.5% CAA diet was verified to increase GPX1a but obstruct Keap1 and GSTP1 expressions, resulting in enhanced SOD activity and reduced MDA levels in plasma. Collectively, the different co-forms of Lys and Glu influenced the growth of juvenile grass carp, and also the muscle development and quality through their different regulation on the protein metabolism, muscle development- and antioxidative-related genes.
本研究旨在比较结晶型 L-赖氨酸和 L-谷氨酸（CAA）、赖氨酸-谷氨酸二肽（KE）对草鱼（Ctenopharyngodon idellus）生长和肌肉发育的影响，并探讨相关的分子机制。分别制备了 5 种实验饲料（CR、0.5% CAA、1.5% CAA、0.5% KE、1.5% KE），其中包含游离（Lys 和 Glu，CAA）和二肽（Lys-Glu，KE）形式的 Lys 和 Glu。将 450 尾初始体重为 10.69±0.07 g 的幼草鱼随机分配到 15 个笼子中，每个笼子 3 个重复，每个重复 30 尾鱼，进行 61 天的喂养。结果表明，0.5% KE 组的增重率（WGR）和特定生长率（SGR）最高，尽管各组之间没有显著差异；添加 0.5% CAA 的饲料显著提高了草鱼的肥满度（CF）和脏体比（VSI）。与 CR 组相比，不同水平的不同 Lys 和 Glu 共形物促进了肌肉氨基酸含量的增加。与 CR 组和其他组相比，0.5% CAA 组的硬度显著增加，0.5% KE 组的弹性更好。0.5% KE 组的肌肉纤维直径和密度与 CR 组有显著差异，且呈负相关。为揭示 Lys 和 Glu 不同共形物引起的差异的相关分子机制，分析了不同饲料对蛋白质吸收、肌肉品质和抗氧化相关基因表达的影响。结果表明，与 CR 组相比，二肽 KE 抑制了与蛋白质代谢相关的基因（如 AKT、S6K1 和 FoxO1a）的表达，但促进了 PCNA 的表达，而 CAA 的游离形式则提高了 FoxO1a 的表达。此外，CAA 共形物组中肌肉发育相关基因（MyoD、MyOG 和 Myf5）的表达显著增强，而 0.5% KE 组中 fMYHCs 的表达被阻断，但 fMYHCs30 显著增加。最后，研究了 Lys 和 Glu 不同共形物对肌肉抗氧化的影响。结果表明，0.5% CAA 饮食增加了 GPX1a，但抑制了 Keap1 和 GSTP1 的表达，导致血浆中超氧化物歧化酶活性增强，丙二醛水平降低。综上所述，Lys 和 Glu 的不同共形物通过对蛋白质代谢、肌肉发育和抗氧化相关基因的不同调节，影响幼草鱼的生长，以及肌肉发育和品质。
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