Effects Of MTOR Activity On Murine Immunological Hepatic Injury And The Mechanism

Mechanistic target of rapamycin (mTOR) is a serine/threonine kinase, and plays a central role in the regulation of cell growth and metabolism. mTOR signal integrates diverse immune and metabolism signals, and regulates innate immune and adaptive immune. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous cell population, which are defined as critical native regulation cells function as immune suppress in tumor, transplant and chronic infection. However, whether mTOR effects on MDSCs still needs to be discovered.In this study, immune-mediated hepatic injury is induced by Con A, and then treats the CIH mice with mTOR inhibitor, rapamycin. It finds that rapamycin treatment protects against immunological hepatic injury by reduced mortality, relieves the damage from serum and tissue levels. The results of flow cytometry show the changes of phenotype and number in liver immune cells. Compared with control group, there is a significantly lower number of CD19+B cells, CD4+T cells, CD8+T cells, NK1.1+cells (P＜0.05), but not F4/80+cells, CD115+monocytes and CD11c+dendritic cells. However, rapamycin treatment significantly increases the number of myeloid CD11b+Gr1+cell (P＜0.05). Moreover, this CD11b+Gr1+cell has the phenotype of CD11b+Gr1+Ly6Chigh, which indicates that mTOR signaling inhibition could induce more CD11b+Gr1+cells. What’s more, when co-cultures CD11b+Gr1+cells which isolated from rapamycin treated CIH liver with T cells, it shows a significantly enhanced immune-suppressive effect on CD4+T cell proliferation, and displayed a phenotype of MDSCs, that is PD-Llhigh, CD206high and CD86low. It suggests that MDSCs are immune suppressive cells and protect against immunological hepatic injury. Cell apoptosis of rapamycin treatment MDSCs is significantly decreased. In addition, the expression of chemokines CXCL1, CXCL2, and their receptor CXCR2, is up-regulated in the MDSCs following rapamycin treatment. And anti-CXCR2antibody injection blocks MDSCs infiltration and resultes in severe mortality, pathological liver damage, and increased ALT and AST levels (P＜0.05). In vivo and vitro studies find that rapamycin treatment promotes MDSCs migration to inflammatory sites, results in the increased number of liver MDSCss. NO, iNOS, arginase levels of liver MDSCs analyzes find the level of iNOS and NO are markedly higher in rapamycin treated CIH mice (P＜0.05), but no significantly change in arginase level. When treats MDSCs with L-NMMA, the inhibitor of iNOS, NO production is significantly reduced, serum ALT level increased and aggravated the liver damage, the recruitment of MDSCs effectively reduced after rapamycin treatment. This indicates mTOR activity down-regulation in MDSCs induced iNOS expression and NO production. When inhibit iNOS, the recrument of MDSCs has been significantly reduced, it indicates that NO is required to promote MDSCs migration with the treatment of rapamycin.This study shows that mTOR protects against murine immunological hepatic injury by promoting the recruitment of MDSCs via NO, and suggests the regulation of mTOR signaling on MDSCs in mmunological hepatic injury, which may provide a potential therapeutic approach to IMH-related diseases.