Extracellular Branched-chain Amino Acids, Especially Valine, Regulate Maturation and Function of Monocyte-derived Dendritic Cells

肝硬变患者树突状细胞(DC)功能受损。众所周知，肝硬变患者血浆支链氨基酸(BCAA)水平降低。虽然氨基酸在许多器官中与维持细胞结构和功能有关，但关于氨基酸(包括支链氨基酸)在免疫系统中的作用的数据有限。本研究旨在探讨支链氨基酸在人单核细胞来源的树突状细胞(MoDC)功能中的作用。从健康志愿者和丙型肝炎肝硬变患者的PBMC中分离CD14阳性单核细胞(CD14(+))。在不含支链氨基酸或缬氨酸的培养液中，单核细胞可分化为未成熟的DC，但不能分化为成熟的DC，且CD83表达较弱。剥夺亮氨酸或异亮氨酸不影响这一过程。在不含支链氨基酸或缬氨酸的培养液中，MODC的同种刺激能力明显降低。Annexin V-FITC/PI染色显示死亡细胞数和凋亡细胞数在任何条件下均无明显差异。免疫印迹结果显示，缺失Valine或Leucine可降低P-S6蛋白的表达。Valine剂量依赖地增加健康志愿者和丙型肝炎肝硬变患者MoDC的同种刺激能力和IL-12的产生。升高的胞外Valine浓度可以改善丙型肝炎肝硬变患者的树突状细胞功能。这些数据为可能有益于肝硬变患者的营养治疗提供了理论依据。

The functions of dendritic cells (DCs) are impaired in patients with liver cirrhosis. It is well known that cirrhotic patients show decreased levels of plasma branched-chain amino acids (BCAA). Although amino acids are associated with maintaining the cell structure and function in many organs, limited data are available regarding the role of amino acids including BCAA in the immune system. We aimed to investigate the roles of BCAA in the function of human monocyte-derived DCs (MoDC). CD14-positive monocytes (CD 14 (+)) were isolated from PBMC from healthy volunteers and HCV cirrhotic patients. In medium deprived of BCAA or valine, monocytes were able to differentiate into immature DCs, but not into mature DCs, and showed their weak expression of CD83. The deprivation of leucine or isoleucine did not affect this process. The MoDC allo-stimulatory capacity was significantly decreased in medium deprived of BCAA or valine. Annexin V-FITC/PI staining showed the numbers of dead and apoptotic cells were not significantly different under any medium. Immunoblotting demonstrated that depletion of valine or leucine decreased P-S6 kinase expression. Valine increased dose-dependently the allo-stimulatory capacity and IL-12 production of MoDC from both healthy volunteers and HCV cirrhotic patients. An elevated extracellular concentration of valine could improve dendritic cell function in HCV cirrhotic patients. These data provide a rationale for nutrition therapy that could be beneficial to patients with cirrhosis.