Table_4_Metabolomics analysis of splenectomy of Nile tilapia (Oreochromis niloticus) reveals the spleen involved in regulating liver lipids and amino acids metabolism.docx

The liver is essential for nutritional balance in fish, and liver damage in farmed fish often arises from factors like overfeeding, causing various health issues. Clinical observations indicate that liver diseases frequently involve spleen dysfunction, and there is evidence to suggest that the spleen has a significant impact on liver function. However, there has been no discussion on the role of the spleen in maintaining liver health in fish. To understand the role of fish spleen in liver metabolism, this study selected Nile tilapia (Oreochromis niloticus) as the experimental material and first established a tilapia splenectomy model. Various biochemical parameters of the liver and serum were measured, and the liver metabolism characteristics of the splenectomy group (SP group) and the sham operation group (SO group) were analyzed using metabolomics. After splenectomy, biochemical parameters of the liver and serum showed abnormalities, including significant increases in total cholesterol (T-CHO) and serum total bile acid (TBA) levels, alongside a significant decrease in liver TBA levels, suggesting impaired metabolic function and cholesterol deposition in the liver. Metabolomics analysis showed that metabolites such as lipids, lipid-like molecules, and organic acids and derivatives were differentially regulated between the SO and SP group. KEGG analysis showed that differential metabolites were enriched in lipid metabolism and amino acid metabolism. The metabolic pathway analysis of differential metabolites showed that after splenectomy, the low-activity urea cycle in the liver may accelerate lipid synthesis, while low concentrations of aromatic amino acids and taurine may inhibit lipid catabolism. These results indicate that after splenectomy, the liver metabolic capacity is impaired, which causes abnormal lipid metabolism by interfering with amino acid metabolism, making splenectomy tilapia liver at risk of liver disease, including cholesterol deposition, hepatic steatosis and nonalcoholic fatty liver disease (NAFLD). Our results show that the spleen is involved in regulating liver lipid and amino acid metabolism, and the spleen may interfere with lipid metabolism by regulating liver amino acid metabolism. Our data can provide support for further research on liver and spleen functions and the immune-nutrient metabolism mechanisms in fish, as well as new ideas for healthy fish farming.

肝脏对于鱼类的营养平衡至关重要，养殖鱼类的肝脏损伤常由过度投喂等因素诱发，进而引发各类健康问题。临床观察显示，鱼类肝脏疾病常伴随脾脏功能异常，且已有研究证据表明脾脏对肝脏功能具有显著影响。然而，目前尚未有针对鱼类脾脏维持肝脏健康作用的相关探讨。为探明鱼类脾脏在肝脏代谢中的作用，本研究选取尼罗罗非鱼（Oreochromis niloticus）作为实验材料，首次构建了罗非鱼脾脏切除模型。本研究检测了肝脏与血清的多项生化指标，并利用代谢组学方法分析了脾脏切除组（SP组）与假手术组（SO组）的肝脏代谢特征。脾脏切除后，肝脏与血清的生化指标出现异常：总胆固醇（T-CHO）与血清总胆汁酸（TBA）水平显著升高，而肝脏TBA水平则显著降低，提示肝脏代谢功能受损并出现胆固醇沉积。代谢组学分析结果显示，假手术组与脾脏切除组间的脂质、类脂质分子以及有机酸及其衍生物等代谢物存在差异表达。京都基因与基因组百科全书（KEGG）富集分析显示，差异代谢物主要富集于脂质代谢与氨基酸代谢通路。差异代谢物的代谢通路分析表明，脾脏切除后，肝脏内活性低下的尿素循环可能加速脂质合成，而芳香族氨基酸与牛磺酸浓度降低则可能抑制脂质分解代谢。上述结果表明，脾脏切除会损伤肝脏代谢能力，并通过干扰氨基酸代谢引发脂质代谢异常，使脾脏切除后的罗非鱼肝脏面临胆固醇沉积、肝脂肪变性及非酒精性脂肪肝病（NAFLD）等肝脏疾病风险。本研究结果证实，脾脏参与调控肝脏脂质与氨基酸代谢，并可通过调节肝脏氨基酸代谢来干预脂质代谢过程。本研究数据可为鱼类肝脏与脾脏功能、免疫-营养代谢机制的后续研究提供支撑，同时为鱼类健康养殖提供新思路。