Key Laboratory of Zoonosis, Ministry of Education, College of Veterinary Medicine, Jilin University, Changchun, Jilin Province, 130062, China.
Mammalian NutriPhysioGenomics, Department of Animal Sciences and Division of Nutritional Sciences, University of Illinois, Urbana 61801.
J Dairy Sci. 2018 Dec;101(12):11175-11185. doi: 10.3168/jds.2018-15120. Epub 2018 Oct 11.
The ability of liver to respond to changes in nutrient availability is essential for the maintenance of metabolic homeostasis. Autophagy encompasses mechanisms of cell survival, including capturing, degrading, and recycling of intracellular proteins and organelles in lysosomes. During negative nutrient status, autophagy provides substrates to sustain cellular metabolism and hence, tissue function. Severe negative energy balance in dairy cows is associated with fatty liver. The aim of this study was to investigate the hepatic autophagy status in dairy cows with severe fatty liver and to determine associations with biomarkers of liver function and inflammation. Liver and blood samples were collected from multiparous cows diagnosed as clinically healthy (n = 15) or with severe fatty liver (n = 15) at 3 to 9 d in milk. Liver tissue was biopsied by needle puncture, and serum samples were collected on 3 consecutive days via jugular venipuncture. Concentrations of free fatty acids and β-hydroxybutyrate were greater in cows with severe fatty liver. Milk production, dry matter intake, and concentration of glucose were all lower in cows with severe fatty liver. Activities of serum aspartate aminotransferase, alanine aminotransferase, glutamate dehydrogenase, and γ-glutamyl transferase were all greater in cows with severe fatty liver. Serum concentrations of haptoglobin and serum amyloid A were also markedly greater in cows with severe fatty liver. The mRNA expression of autophagosome formation-related gene ULK1 was lower in the liver of dairy cows with severe fatty liver. However, the expression of other autophagosome formation-related genes, beclin 1 (BECN1), phosphatidylinositol 3-kinase catalytic subunit type 3 (PIK3C3), autophagy-related gene (ATG) 3, ATG5, and ATG12, did not differ. More important, ubiquitinated proteins, protein expression of sequestosome-1 (SQSTM1, also called p62), and microtubule-associated protein 1 light chain 3 (MAP1LC3, also called LC3)-II was greater in cows with severe fatty liver. Transmission electron microscopy revealed an increased number of autophagosomes in the liver of dairy cows with severe fatty liver. Taken together, these results indicate that excessive lipid infiltration of the liver impairs autophagic activity that may lead to cellular damage and inflammation.
肝脏对营养可用性变化的反应能力对于维持代谢稳态至关重要。自噬包括细胞存活的机制，包括在溶酶体中捕获、降解和回收细胞内蛋白质和细胞器。在负营养状态下，自噬为维持细胞代谢提供底物，从而维持组织功能。奶牛严重的负能量平衡与脂肪肝有关。本研究旨在研究严重脂肪肝奶牛的肝自噬状态，并确定与肝功能和炎症标志物的相关性。在产犊后 3 至 9 天，从临床健康的奶牛（n=15）或严重脂肪肝奶牛（n=15）中采集多胎奶牛的肝和血样。通过针穿刺进行肝组织活检，并通过颈静脉穿刺连续 3 天采集血清样本。严重脂肪肝奶牛的游离脂肪酸和β-羟丁酸浓度较高。严重脂肪肝奶牛的产奶量、干物质摄入量和葡萄糖浓度均较低。严重脂肪肝奶牛的血清天门冬氨酸氨基转移酶、丙氨酸氨基转移酶、谷氨酸脱氢酶和γ-谷氨酰转移酶活性均较高。严重脂肪肝奶牛的血清结合珠蛋白和血清淀粉样蛋白 A 浓度也明显升高。严重脂肪肝奶牛肝脏自噬体形成相关基因 ULK1 的 mRNA 表达降低。然而，其他自噬体形成相关基因，如 beclin 1（BECN1）、磷脂酰肌醇 3-激酶催化亚基 3（PIK3C3）、自噬相关基因（ATG）3、ATG5 和 ATG12 的表达没有差异。更重要的是，泛素化蛋白、自噬体相关蛋白 1 轻链 3（MAP1LC3，也称为 LC3-II）的表达和微管相关蛋白 1 轻链 3（MAP1LC3，也称为 LC3-II）的表达均在严重脂肪肝奶牛中升高。透射电子显微镜显示，严重脂肪肝奶牛肝脏中的自噬体数量增加。综上所述，这些结果表明，肝脏中过多的脂质浸润会损害自噬活性，从而导致细胞损伤和炎症。
